Sensory and Related Techniques for Evaluation of Dairy Foods ...

Course Compendium Sensory and Related Techniques for Evaluation of Dairy Foods 23rd Short Course Organized under the aegis of Centre of Advanced Studies in Dairy Technology

17th June, 2008 to 7th July, 2008 Course Director Dr. Dharam Pal Course Coordinator Dr. Ashish Kumar Singh Centre of Advanced Studies Dairy Technology Division National Dairy research Institute Karnal 132001 (Haryana), India 2008

Published by Dr. A. A. Patel Head, Dairy Technology Division Director, CAS

Course Director Dr. Dharam Pal

Course Coordinator Dr. Ashish Kumar Singh

Editing and Compilation Dr. Dharam Pal Dr. V.K. Gupta Dr. R.R.B. Singh Dr. Mrs. Latha Sabikhi Dr. A.K. Singh Dr. Sumit Arora

All Right Reserved © No part of this lecture compendium may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photography, recording or any other information storage and retrieval system without the written permission from the Director, NDRI, Karnal

Cover Design and Page Layout Mr. Avneet Rajoria & Mr. Ramesh Modi

i

Committees for the Course Organization

ORGANIZING COMMIITTEE

Dr A. A. Patel (Director, CAS) Dr. S. Singh Dr. G. K. Goyal Dr. V. K. Gupta Dr. S.K. Kanawjia Dr. D. K. Thompkinson Dr. Dharam Pal (Course Director) Dr. Ashish Kumar Singh (Course Coordinator)

TECHNICAL COMIITTEE

RECEPTION COMMITTEE Dr. G. K. Goyal (Chairman) Dr. Ashish Kumar Singh Mr. Ram Swaroop

Dr. V. K. Gupta (Chairman) Dr. R. R. B. Singh Dr. (Mrs.) Latha Sabikhi

HOSPITALITY COMMITTEE

PURCHASE COMMITTEE

Dr. S. K. Kanawjia (Chairman) Dr. (Mrs.) Latha Sabikhi Mr. Lahiri Singh

Dr. D. K. Thompkinson (Chairman) Mr. F. C. Garg Mr. M. K. Trehan

ii

Short Course on Sensory and Related Techniques for Evaluation of Dairy Foods 17th June - 7 July, 2008 Course Programme

10.:00 AM- 10.15 AM

17.06.2008 (TUESEDAY) Registration

10.15 AM-10.50 AM 11.00 AM-11.45 AM 11.45 AM-1.00 PM 1.00 PM- 2.00 PM 2.15 PM -3.30 PM 3.30 PM- 3.45 PM 3.45 PM- 4.30 PM

Visit to ATIC Inauguration of Course Visit to Experimental Dairy Plant Lunch Visit to Model Dairy Tea Visit to Library

9:45 AM-10.45 AM 10.45 AM-1.00 PM 1.00 PM – 2.00 PM 2.15 PM- 3.15 PM 3.15 PM - 3.30 PM 3.30 PM – 4.30 PM

18.06.2008 (WEDNESDAY) Requirements for Sensory Evaluation of Foods (Theory) Determination of Taste threshold (Practical) Lunch Determination of Odour threshold (Practical) Tea Library Consultation

Dr. Ashish Kumar Singh Mr. M. K. Trehan Mr. M. K. Trehan Mr. M. K. Trehan Mr. M. K. Trehan Dr. Dharam Pal

Dr. Dharam Pal Mr. Ramswaroop Dr. Dharam Pal Mr. Ramswaroop -

19.06.2008 (THURSDAY) 9:45 AM- 10.45 AM

Sensory Methods and their Applications in Evaluating Quality of Foods (Theory)

10.45 AM- 1.00 PM

Sensory Evaluation of Milk (Theory & Dr. Dharam Pal Practical) Mr. Ramswaroop Lunch Sensory Evaluation of Dried Milk and Dr. V. K. Gupta Milk Products (Theory) Tea Library Consultation

1.00 PM- 2.00 PM 2.15 PM- 3.15 PM 3.15 PM - 3.30 PM 3.30 PM – 4.30 PM 9:45 AM- 1.00 PM

20.06.2008 (FRIDAY) Determination of Water Activity of Foods (Theory & Practical) iii

Dr. Dharam Pal

Dr. R. R. B. Singh Mr. Avneet

Rajoria 1.00 PM – 2.00 PM 2.15 PM- 3.15 PM 3.15 PM-3.30 PM 3.30 PM-4.30 PM 9:45 AM- 10.45 AM 10.45 AM-1.00 PM 1.00 PM – 2.00 PM 2.15 PM- 3.15 PM 3.15 PM - 3.30 PM 3.30 PM – 4.30 PM

9:45 AM- 1.00 PM 1.00 PM – 2.00 PM 2.15 PM- 3.15 PM 3.15 PM -4.30 PM

9:45 AM- 10.45 AM 10.45 AM-1.00 PM 1.00 PM – 2.00 PM 2.15 PM- 4.30 PM

9:45 AM- 10.45 AM 10.45 AM-1.00 PM 1.00 PM – 2.00 PM11 2.15 PM- 4.30 PM

Lunch Principles of Good Laboratory Practice (Theory) Tea Library Consultation 21.06.2008 (SATURDAY) Chemistry of Flavour Development in Cheese (Theory) Microstructure of Dairy Products (Theory & Practical) Lunch Consumer Acceptance Studies (Theory)

Dr. Rajan Sharma Dr. Sumit Arora Dr. S. K. Tomar Dr. (Mrs.) Latha Sabikhi

Tea Colour Measurement of Foods (Practical)

23.06.2008 (MONDAY) Sensory Attributes of Ice-cream and Frozen Dessert (Theory & Practical) Lunch Viscoelastic Characteristics of Foods (Theory) Sensory Evaluation of Milk Chocolate (Practical)

Dr. Ashish Kumar Singh Mr. .Avneet Rajoria Mr. F. C. Garg Mr. Ramswaroop Dr. G. R. Patil Dr. Ashish Kumar Singh Mr. Modi Ramesh

24.06.2008 (TUESDAY) Statistical Techniques for Analysis of Dr. R. Malhotra Sensory Data (Theory) Sensory Evaluation of Dried Milks (Practical) Lunch Texture Measurement of Dahi & Yoghurt Dr. Dharam Pal (Practical) Mr. N. Raju 25.06.2008 (WEDNESDAY) Analytical techniques for Characterization of Flavoring Compounds in Dairy Products (Theory) Descriptive Sensory Analysis of foods (Practical) Lunch Sensory evaluation of Paneer and Unripened Cheeses (Theory & Practical)

iv

Dr. Rajesh Bajaj Dr. Ashish Kumar Singh Dr. S. K. Kanawjia

9:45 AM- 1.00 PM 1.00 PM – 2.00 PM 2.15 PM- 4.30 PM

9:45 AM- 10.45 AM 10.45 AM-11.15 AM 11.15 AM-11.30 AM 11.30 AM-1.00 PM 1.00 PM – 2.00 PM 2.15 PM- 4.30 PM

9:45 AM- 1.00 PM 1.00 PM – 2.00 PM 2.15 PM-4.30 PM

9:45 AM- 10.45 AM 10.45 AM-1.00 PM 1.00 PM – 2.00 PM 2.15 PM- 3.15 PM 3.15 PM-3.30 PM 3.30 PM-4.30 PM 9:45 AM- 1.00 PM 1.00 PM – 2.00 PM 2.15 PM- 4.30 PM

26.06.2008 (THURSDAY) Sensory and Rheological Properties of Fermented Milks (Theory & Practical) Lunch Sensory Evaluation of Khoa & Khoa based Sweets (Theory & Practical) 27.06.2008 (FRIDAY) Biosensors in Chemical Quality Assessment of Dairy and Food Products (Theory) Nutritional and Therapeutic Assessment Techniques for Dairy Products (Theory) Tea break Texture Profile Analysis of Dairy Products (Practical) Lunch Sensory Characteristics of Milk Protein Products (Theory)

Dr. (Mrs.) Latha Sabikhi Mr. Ram Swaroop Mr. F. C. Garg Mr. Ram Swaroop Dr. Rajan Sharma Dr. (Mrs.) Suman Kapila Dr. R. R. B. Singh Mr. Avneet Rajoria Dr. V. K. Gupta

28.06.2008 (SATURDAY) Statistical Software for Analysis of Dr. R. Malhotra Sensory Data (Theory & Practical) Lunch Sensory Characteristics of Concentrated Dr. R. R. B. Singh and UHT Milk (Theory & Practical) 30.06.2008 (MONDAY) Influence of Packaging Materials on Sensory Quality of Dairy Products (Theory) Testing of Packaging Materials for Dairy Foods (Practical) Lunch Chemistry of Quality Attributes in Heat Processed Dairy products (Theory)

Dr. G. K. Goyal Dr. G. K. Goyal Mr. Ram Swaroop Dr. (Mrs.) Bimlesh Mann

Tea

Library Consultation 1.07.2008 (TUESDAY) Descriptive Sensory Analysis of Dairy Foods (Theory & Practical) Lunch Role of Starter and Adjunct Cultures on Quality Characteristics of Fermented Dairy Products (Theory)

v

Dr. Ashish Kumar Singh & Ms. Rekha Chawla Dr. Rameshwar Singh

9:45 AM- 10.45 AM 10.45 AM- 11.00 AM 11.00 AM- 1.00 PM 1.00 PM – 2.00 PM 2.15 PM- 4.30 PM

9:45 AM- 1.00 PM 1.00 PM – 2.00 PM 2.15 PM- 3.15 PM

2.07.2008 (WEDNESDAY) Role of Primary Senses in Sensory Evaluation of Foods (Theory) Tea Techniques for Sensory Evaluation of Beverages (Theory & Practical) Lunch Judging Contest for Participants 3.07.2008 (THURSDAY) Sensory Characteristics of Fat-rich Dairy Products (Theory & Practical) Lunch Emerging Concepts in Sweet Taste

Prof. V. K. Joshi Prof. V. K. Joshi Dr. Dharam Pal Mr. Ramswaroop Dr. A. A. Patel Mr. Ramswaroop Dr. Sumit Arora

(Theory) 3.15 PM-3.30 PM 3.30 PM- 4.30 PM

9:45 AM- 1.00 PM 1.00 PM – 2.00 PM 2.15 PM- 4.30 PM

Tea Rheological & Textural Characteristics of Solid Foods (Theory) 4.07.2008 (FRIDAY) Basic Concepts of Rheology and Texture Measurement of Foods (Theory) Lunch Properties of Food Powders (Theory & Practical)

Dr. A. A. Patel

Dr. D. S. Sogi Dr. R. R. B. Singh Mr. Avneet Rajoria

5.07.2008 (SATURDAY) 9:45 AM- 10.45 AM

10.45 AM- 1.00 PM 1.00 PM – 2.00 PM 2.15 PM- 3.15 PM 3.15 PM - 3.30 PM 3.30 PM –4.30 PM 9:45 AM- 10.45 AM 10.45 AM-11.15 AM 11.15 AM-1. 00 PM 1.00 PM – 2.00 PM 2.30 PM- 3.30 PM

Concept of Colour Measurement and Sampling Techniques for Quality Evaluation of Food (Theory) Sensory Characteristics of Ripened Varieties of Cheeses (Theory & Practical) Lunch Nondestructive methods for Quality Evaluation of Dairy and Food Products (Theory) Tea & Discussion 7.07.2008 (MONDAY) Course Evaluation Interaction with the Course Faculty Lunch Valedictory function

vi

Dr. S. N. Jha

Dr. S. Singh Dr. S. N. Jha

CONTENTS Foreword

Dr. A.K. Srivastava

i

Committees for Course the Course Organization

ii

Course Programme

iii

1

Requirements for Sensory Evaluation of Dr. Dharam Pal Foods

1

2

Sensory Methods and their Applications Dr. Dharam Pal in Evaluating Quality of Foods

10

3

Sensory Evaluation of Milk

Dr. A.K. Singh

18

4

Sensory Characteristics of Fresh Cheese

Dr. S.K. Kanawjia

25

5

Sensory Attributes of Ice Cream

Mr. F.C. Garg

33

6

Sensory Evaluation of Dairy Products V. Pathak & Z.F. Bhat with Special Emphasis on Flavour Lexicon

40

7

Sensory Attributes of Concentrated Milk Dr. R.R.B. Singh and their Evaluation

48

8

Sensory Attributes of Fermented Milk Dr. Latha Sabikhi Products

56

9

Application of e-tongue in monitoring

65

Dr. S.K. Kanawjia

Sensory quality of foods 10

Role of Packaging Materials In Enhancing Dr. G.K. Goyal Sensory Quality of Dairy Products

77

11

Consumer Acceptance Studies

83

12

Chemistry of Flavour Development In Dr. Sumit Arora Cheese

86

13

Analytical Techniques for Dr. Rajesh Kumar, Characterization of Flavouring Dr. R. B. Sangwan and Compounds In Dairy Products Dr. Bimlesh Mann

97

14

Sensory Attributes Products

Protein Dr. Vijay Kumar Gupta

104

15

Sensory Evaluation of Dried Milk and Dr. Vijay Kumar Gupta Milk Products

110

16

Application of Rheology in Quality Dr. Dalbir Singh Sogi Assurance in Food Processing

116

of

Milk

Dr. Latha Sabikhi

17

Nondestructive Methods for Quality Dr. S. N. Jha Evaluation of Dairy and Food Products

126

18

Good Laboratory Practices – Genesis & Dr. Rajan Sharma Concept

135

19

Chemistry of Quality Attributes in Heat Dr. (Mrs.) Bimlesh Processed Dairy Products Mann

144

20

Determination of Sorption Isotherms and Dr. R. R. B. Singh Generation of Sorption Data

155

21

Biosensor in Chemical Quality Assessment of Dairy and Food Products Dr. Rajan Sharma

165

22

Soft Computing Models Applications to Dairying

with Dr. A. K. Sharma

177

23

Microstructure of Products: An Update

Dairy Dr. Sudhir Tomar

184

24

Nutritional and Therapeutic Assessment Dr. Suman Kapila for Functional Dairy Products

196

25

Viscoelastic Behaviour of Foods

Dr. G. R. Patil

208

26

Fundamentals of Rheology

Dr. Dalbir Singh Sogi

214

27

Switching Approach

28

Concept of Colour Measurement and Dr. S. N. Jha Sampling Techniques for Quality Evaluation of Food

227

29

Sensory Evaluation of Ripened Varieties Dr. S. Singh of Cheese

245

30

Statistical Techniques for Analysis of Dr. Ravinder Malhotra Sensory Data

254

31

Descriptive Sensory Analysis

267

Cultured

Sweeteners

–

A

Sweet Dr. Sumit Arora

Dr. A. K. Singh

221

REQUIREMENTS FOR SENSORY EVALUATION OF FOODS Dr. Dharam Pal Principal Scientist Division of Dairy Technology National Dairy Research Institute, Karnal.

1.0

INTRODUCTION

A number of quality assurance procedures are used to examine and maintain quality of a dairy product. The testing starts from reception of raw material, for example, milk, to close examination of finalized product. These tests are physical, chemical, microbiological, instrumental and sensory. In our country, the dairy industry so far considers the chemical and microbiological quality as the sole criteria of deciding food quality. With the availability of more milk, increased competition and consumers’ awareness about quality, the significance of sensory evaluation is being realized and it is emerging as an important analytical tool in fast growing dairy industry. Sensory evaluation may be defined as a scientific discipline used to evoke, measure, analyze and interpret results of those characteristics of foods and materials as they are perceived by the senses of sight, smell, taste, touch and hearing. The sensory evaluation is very important in product evaluation on account of following advantages: i)

It is a simple analytical tool,

ii)

It identifies the presence or absence of perceptible differences in terms of flavour, texture, colour and appearance,

iii)

These important quality attributes are measured in a fast and quantifiable manner employing sensory techniques. The use of chemical and instrumental methods for examining sensory characteristics are time consuming, complicated and expensive,

iv)

It enables identification of a particular problem or defect that cannot be detected by other analytical techniques,

v)

Sensory evaluation techniques help in ensuring that the consumers get a non defective and enjoyable product.

In recent years, the competition in food/dairy corporate has tremendously increased. The food processing companies are making very fast changes in their existing product in terms of ingredients, value addition, packaging etc. or developing new products to grab larger global market share. In all these situations, sensory

Sensory and Related Techniques for Evaluation of Dairy Foods

1

evaluation plays a critical role. The various applications of sensory evaluation are given as below: • • • • • • • • 2.0

Inspection of raw materials New product development improvement/reformulation of existing product Cost reduction Quality assurance Selection of packaging material Shelf life studies Establishing analytical/ instrumental/ sensory relationships REQUIREMENTS

A successful implementation of sensory evaluation programme requires following three major components: • Proper laboratory facilities • Sensory panels and their rigorous training programmes • Statistician 2.1

Laboratory Set Up

Many designs of the sensory evaluation laboratory are available. The sensory laboratory set up normally consists of a reception cum briefing room, panel booths and preparation room. Sensory evaluation should be conducted in quiet and well lit rooms free from any odours. The dominant motive of constructional details should be to have comfort for concentrated prolonged testing and ease of cleaning. Pleasing neutral shades and maintenance of comfortable temperature and humidity conditions of the whole area or at least the panel room are desirable. The testing area where booths are located should be separated from sample preparation room and wash room and store by a complete partition. 2.1.1 Reception and briefing room It should be so designed as to ensure maintenance of pleasant attitudes and minimize traffic to the booths. Panel members shall assemble here, register, receive the evaluation card and briefed about the test. 2.1.2

Testing booths/area:

This is the area where panel members carry out actual sensory evaluation of dairy products. Testing area shall be located separately but in the immediate vicinity of the preparation area. This area is normally divided in small booths (number of booths between 5 to 10) so that each panel member can independently evaluate the product. Following conditions have to be maintained in testing area for obtaining best results: -

The temperature and relative humidity shall be constant, controllable and comfortable for evaluators. A temperature of about 20oC and 62% relative humidity are considered to be optimum.


2

-

Noise level shall be kept to a minimum during the tests. The movement of persons shall also be restricted in the area.

-

The testing area shall keep free from odours. A slight positive pressure may be created in the testing area to reduce inflow of odorous air from other area.

-

Lighting is very important in all sensory testing. It is particularly important in colour examination of dairy products. Lighting particularly in testing booths shall be uniform, shadow free, controllable and of sufficient intensity to permit effective evaluation of the colour and appearance of samples. In most cases, lights having a correlated colour temperature of 6500 K (or 110 candle foot light) are desirable. In order to mask differences in colour and other appearance characteristics special lighting devices, such as a dimmer device, colored lamps/filters or sodium vapour lamps, may be provided.

-

The size of each testing booth shall be sufficiently large to accommodate the samples, utensils, sink, rinsing agents and score sheet/card. An area of 0.9 m wide and 0.6 m deep is considered optimum for this purpose. The height of working space in the booth should be appropriate to allow comfort to the evaluator.

-

A counter on the serving/distribution area side shall be provided. Openings, covered by sliding doors, of convenient size may be provided for supplying samples into the booths from the serving counter. A system, such as light bulb on the counter side, is devised for evaluator to signal to the operator when he is ready for a sample.

2.1. 3 Preparation room It shall be suitably separated from the testing room and should be equipped for preparing and serving food samples. The room should have the facility for cooking range hot and cold storage cabinet. The ventilation should be proper and the cooking odours should not penetrate the panel booth area. The samples shall be passed to the test booths through hatch in the partition. The hatch on the service counter should preferably be constructed in such a manner that there shall be no recognition of individual or either side of partition. The laboratory facility should be flexible enough to handle enough to handle current and future testing activities as well as to provide a workable environment for the staff. The use of computers has been recommended for sensory evaluation work. In that case, sensory evaluation laboratory should include space for data processing equipment. 3.0

SELECTION OF SENSORY PANELISTS

Analysis of sensory properties of food involves the use of human subjects in the laboratory/processing plant environment. The sensitivity and experience of an evaluator (panelist) influence the accuracy of results. The evaluator should work like a calibrated instrument and provide reproducible results. The selection of most stable


3

and sensitive panel members and their training, is therefore, very essential for efficient conduct of sensory analysis of dairy products. 3.1

Types of panel

The sensory panels are classified into three categories viz., trained, semi trained and consumer panel. The panelists are selected and trained by the sensory leader/coordinator depending on the type of the product. Trained Panel: They should be carefully selected and trained, and need not be expert panelists. The trained panel should be used to establish the intensity of a sensory character or overall quality of a food. A trained panel should comprise of small number of members varying from 5 to 10 and may be used in all developmental, processing and storage studies. A small highly trained panel will give more reliable results than a large untrained panel. Semi-Trained Panel (D&C Panel): This type of panel should be constituted from persons normally familiar with quality of milk and different classes of dairy products. This panel is capable of discriminating differences and communicating their reactions, though it may not have been formally trained. In a semi-trained panel individual variations can be balanced out by involving greater number of panelists. The panel, should normally consist of about 25 to 30 members, and should be used as a preliminary screening programme to select a few products for large scale consumer trials. Consumer Panel: The members of the consumer or untrained panel should be selected at random and ensure due representation to different age, sex, race and income groups in the potential consumer population in the market area. More than 80 members are required to constitute a consumer panel. Two channels can be adopted for screening and selection of sensory panel members. First, from the quality control/research laboratory and second source is from the processing unit. Another option is to have a mixed source i.e. some of the members from quality control laboratory/research laboratory and the remaining from processing sections. Normally double the numbers of panelists finally required are selected. For example, if 7 members are needed in the final panel at least 15 should be initially screened 3.1.2

Qualification for Screening a Panelist

Interest and motivation: Candidates who are interested in sensory analysis and have investigating curiosity are likely to be more motivated and will do better jobs. Attitudes to foods: Candidates having strong liking or disliking towards a dairy product should not be screened. Knowledge and aptitude: The evaluators should have capacity to concentrate and to remain unaffected by external influences. He should have knowledge about basic aspects and principles of milk and its processing into products.


4

Health: Candidates should be in good general health. They shall not suffer from any disabilities, which may affect their senses, or from any allergies or illness and shall not take medication, which might impair their sensory capacities. Ability to Communicate: The ability of candidates to communicate and describe the sensations they perceive when judging a food product is particularly important. Availability: Candidates shall be available to attend both training and subsequent evaluation. Personnel who travel frequently or have heavy workloads are often unsuited for sensory work. Table 1. Examples of materials/substances and their concentration for identification/ matching test Taste or odour

Material

Concentration in water (taste material) or ethanol* (odorous material) at room temperature (g/litre)

Taste Sweet

Sucrose

16

Acid/ sour

Tartaric acid or citric acid

1

Bitter

Caffeine

0.5

Salty

Sodium chloride

5

Astringent

Tannic acid or potassium aluminium sulfate (alum)

1 0.5

Metallic

Ferrous sulfate**, hydrates, FeSO4.7H2O

0.01

Lemon, fresh

Citral (C10H15O)

1 x 10-3

Vanilla

Vanillin (C8H8O3)

1 x 10-3

Thyme

Thymol (C10H14O)

5 x 10-4

Odour

Floral, Jasmine Benzyl acetate (C8H12O2) 1 x 10-3 * Stock solutions are prepared with ethanol, but the final dilution is made with water and shall not contain more than 2% of alcohol. ** To mask yellow colour, present the solutions in closed opaque containers or under dim or colouring light. Test for Detection of Basic Taste: Solutions of four basic taste solutions, namely sweet, sour, salt and bitter are prepared of the concentration as shown in table 2 below:


5

Table 2. Concentration of taste solutions used to examine the acuity of candidates Taste Quality

Concentration in water at room temperature

Caffaine

Bitter

0.27 g/ litre

Citric Acid

Sour

0.60 g/ litre

Sodium Chloride

Salt

2 g/ litre

Material

Sucrose Sweet 3.1.3 Screening and Selection

12 g/ litre

Sensory panelists can be screened and selected by adopting several tests. The followings are the most commonly used tests: • determine impairment of primary senses (colour, vision, ageusia and anosmia) • matching test for taste and odour substances • ability to detect basic taste and odour acuity • determine ability to characterized texture • performance in comparison with other candidates Colour Vision: Candidates with abnormal colour vision or colour blindness are unsuitable for judging of dairy products. Assessment of colour vision can be carried out by a qualified optician. Matching Test: Samples of sapid and/ or olfactory materials, depending on the nature of product for which the panel members are to be trained later, at well above threshold levels of the expected panelists are prepared. The examples of these materials are given in table 1. Each sample is allotted a different, random, three digit code number. Candidates are presented with one sample of each type and are allowed to familiarize themselves with them. They are then presented with a series of the same materials labelled with different code numbers. They may be asked to match each of them with one of the original set and describe the sensation they are experiencing. For the substances and their concentration given in table 1, candidates who make fewer than 80% correct answers should not be chosen as selected panelists. These test materials along with blank (water) are presented to the candidates and asked them to detect the taste quality. Preferably candidates should have 100% correct responses as the concentrations test materials are at the super threshold level. Inability to detect differences and identify the taste quality after several repetitions indicate that the candidates have poor sensitivity and unsuitable to judge the samples on the basis of taste. Odour Recognition Test: Candidates are presented many (about 10 in each lot) odoriferous substances. Some of these materials are familiar (those we use daily such as tea, coffee, onion, garlic, curd, orange, spices, etc.) and others unfamiliar (table 3). The odorous food materials may be presented preferably in form of liquid extract or as such (in a test tube in invisible form). The concentration should be above the Sensory and Related Techniques for Evaluation of Dairy Foods

6

recommended threshold level. Candidates are graded according to correct answers. Those recognize less than 65% of odorous substances/odour are unsuitable as panelist for this type of test. Table 3. Examples of unfamiliar odorous material for odour recognition test Material

Name most commonly associated with the odour

Benzaldehyde

Bitter almonds, cherry, …..

Octene-3-Ol

Mushroom, ……

Phenyl-2-ethyl acetate

Floral, ……

Diallyl sulphide

Garlic, ……

Camphor

Camphor, medicine, ……

Menthol

Peppermint, ……

Butyric acid

Rancid butter, ……

Acetic acid

Vinegar, ……

Isoamyl acetate

Fruit, banana, ……

Thymol

Spices, ……

Vanillin

Vanilla, ……

Textural characterization: This type of test is highly beneficial for selecting the panelists for judging the dairy products where texture is an important attribute like cheese, paneer, butter, ice cream, khoa etc. In this test, all range of products having typical texture (table 4) is given to the candidates. They have to arrange these products according to the nature and level of textural properties, such as hard, elastic (spongy), adhesive (sticky/pasty), brittle, gummy, cohesive, chewy etc. A satisfactory level of success in this task can be specified only in relation to the products used. Candidates who achieve less than 65% of the maximum score are unsuitable. Table 4. Food products with typical textural attributes Food product Carrot (raw) Butter Toffee Meat/ Paneer Biscuit Rasogolla Oranges Chest nut puree Semolina Salt

Textural attribute most commonly associated Hard, crunchy Soft Gummy Chewy Brittle Spongy Juicy, cellular particles Pasty Grainy Gritty/ coarse


7

3.1.4

Training

The purpose of training is to increase sensory acuity of panelists and provide them with rudimentary knowledge of procedures used in sensory evaluation. Training also develops the ability of panel members to detect, recognize and describe sensory stimuli related to food products. A general step-wise approach for training in food/dairy product is summarized as below: a) Sensory panelists (assessors or evaluators) should be explained the basic requirements of sensory evaluation i.e. what they should do and what not to do. b) Assessors shall be acquainted with the: -

desirable and undesirable attributes of the product correct terminology use of score card scoring technique/ sequence of observations

c) Samples used for training and testing shall be characteristic of their origin, style and quality, and representative of the range generally found in the market (all defects may be simulated in the samples under laboratory conditions). A reference (having most desirable characters) is always provide with test samples. d) Difficulties of the test are so adjust the that the group as a whole will find difference between the samples, but some panelists will fail. e) Start with the large group and reject those who are insensitive or under perform. f) Finally a trained panel comprising of 5-6 members is retained. 4.0

STATISTICIAN

The role of a statistician is very important in sensory evaluation programme at each stage starting from designing of experiments till drawing valid conclusions from the sensory data. A statistician help in planning of experiment coding and presentation of samples, statistical analysis of data by applying appropriate design and interpretation of results. Though, now a days several softwares are available for statistical analysis, the role of statistician in tabulation of data and drawing of inferences is equally important. 5.0

SAMPLING REQUIREMENTS

i) Sampling should be carried out by a trained and experienced person and it is essential that the sample should be representative of the lot. ii) A procedure of sample preparation which is most likely to bring out the difference in the particular quality attribute under evaluation shall be selected. Care shall be taken that no loss of flavor occurs and no foreign tastes or odours are imported by the procedure during preparation, storage, serving, etc. Depending upon the nature of the material and aim of the test, the need for a medium in testing auxiliary items should be decided. Foods like hot sauce, spices, vinegar, etc. may require dilution with some medium because of their intense physiological efforts.


8

iii) The panelist should be allowed to have sufficient sample necessary to make judgment. Unless, only one sample is to be tested, full normal serving quantities shall not be served even though the material is available. iv) The temperature of serving should be close to that recommended for the food product. The samples shall be served in utensils of the same type and appropriate size, shape and colour and they shall not import any taste or odour to the sample. The test should be carried out at least one hour before or after lunch. v) Use of materials which are likely to vitiate results such as smoking, chewing, pan (betel-vine) and taking intoxicants by a panelist should have a time lapse of at least half-an-hour before the test. Use of strong odoriferous substances such as cosmetics, flowers, hair oil should be avoided. vi) The number of samples served in any session shall depend upon the nature of the test product and upon the evaluation method use. In case the test product exert mild sensory effects, large number of the products exerting strong prolonged sensory effects, the number of samples may be reduced to less than 5. vii) Since coding is necessary to obscure the identity of the sample, a multiple digit code generated from a table of random numbers should be used. Avoid constant use of certain codes or a set of codes to expedite tabulation of results. 6.0

EVALUATION CARD

The evaluation card should be clearly printed and the matter should be arranged in logical sequence for examination which is expected under each test. Appropriate terminology without ambiguity shall be used. The evaluation card should be simple, brief, easy to follow and record what is exactly required. Due weightage should be given to all the sensory attributes. 7.0

REFERENCES

Amerine, M. A., Pangborn, R. M. and Roessler, E. B. (1965). Principles of Sensory Evaluation of Food Academic Press, New York. ASTM (1986). Manual on Sensory Testing Methods. STP 434, American Society for Testing and Materials, Philadelphia, U.S.A. Bodyfelt, F.W., Tobias, J. and Trout, G.M. (1988). The Sensory Evaluation of Dairy Products, AVI Publ. Co., New York. Dharam Pal, Sachdeva, S. and Singh, S. (1995). Methods for determination of sensory quality of foods: A critical appraisal. J. Fd. Sci. Technol. 32 (5):357-367. Russell, G. M. (1984). Some basic consideration in computerizing the sensory laboratory. Food Technol. 38(9): 67-70. Stone, H. and Sidel, J. (1993). Sensory Evaluation Practices, Academic Press, Inc. London.


9

SENSORY METHODS AND THEIR APPLICATIONS IN EVALUATING QUALITY OF FOODS Dr. Dharam Pal Principal Scientist Division of Dairy Technology National Dairy Research Institute, Karnal. 1.0

INTRODUCTION Sensory tests are conducted to meet the following purposes: • Select qualified judges and study human perception of food attributes. • Correlate sensory with chemical and physical measurement. • Study processing effects, maintain quality, evaluate raw material selection, establish storage stability or reduce costs. • Evaluate quality or • Determine consumer reaction.

Each of these purposes requires appropriate tests. There are a substantial number of test methods and new methods continue to be developed. Stone and Sidel (1993) have classified these methods into following categories.

S.No.

Category

Test Type

1.

Discriminative Paired comparison, Duo trio, Triangle, Dual standard, Multiple standard, etc.

2.

Descriptive

Flavor profile, Texture profile and Quantative Descriptive Analysis (QDA)

3.

Affective

Acceptance/ preference: 9-points Hedonic scale, Consumer studies

4.

Others

Scoring, Ranking

2.0

DISCRIMINATIVE TESTING

This is one of the most useful analytical tools available to the sensory professionals. It is on the basis of a perceived difference between two products that one can justify proceeding to a descriptive test in order to identify the basis for the difference. Within this general class is variety of specific methods as given in the table above. The main objective of all these methods is to answer a simple question. “Are the products perceived as different”? Obviously the response to this question can have major consequences. If the conclusions from a discrimination test are to be accepted by management as reliable, valid and believable, then it is important that each test be Sensory and Related Techniques for Evaluation of Dairy Foods

10

conducted with proper consideration for all aspects of the test design, product preparation and handling, implementation, data analysis and interpretation. 2.1

Paired Comparison Test The paired comparison procedure is the earliest example of the application of discrimination testing to food and beverage evaluation. It has also been used successfully for determinations of threshold for basic taste solutions. The paired comparison test is a two product test, and the panelist task is to indicate the one that has more of a designated characteristic such as sweetness, tenderness or skinniness. This method is also identified as a directional paired comparison test, the “directional” component altering the panelist to a specific type of paired test. The paired comparison test is relatively easy to organize and to implement. The two coded products (AA, BB, AB and BA) are served simultaneously and the subject has to decide whether “there is difference” or “there is no difference”. Requiring a “difference” response in all cases has been found to give better results. Another version of the paired test is the A-not-A procedure. The subject is presented with a single sample for evaluation, which is then replaced by a second sample. The subject then makes a decision as to whether the products are same (or different). This particular test procedure has considerable merit in those situations where non test variables such as a colour difference may influence results. 2.2

Duo-trio and Triangle test

These tests have been discussed earlier. The Duo-trio test is suitable for products that have relatively intense taste, odour and / or kinaesthetic effects such that the sensitivity is significantly reduced. It lends itself to use for quality control and for selection of judges for superior discrimination. The chance probability associated with the duo-trio test is identical with that of the other two product tests. Whenever products are being compared with a current franchise (i.e. product now being manufactured), the duo-trio, constant-reference test method, is most appropriate. The chance probability associated with the three product (triangle) test is only 1/3, which accounts for its claim of greater sensitivity. The triangle test is more difficult test because the subject must recall the sensory characteristics of two products before evaluating a third and then making a decision. In fact, the test can be viewed as a combination of three paired tests (A-B, A-C and B-C). Products that have intense flavours and aromas that are spicy and/or are difficult to remove from palate, or that have physiological effects (distilled beverages) usually preclude the use of the triangle test. 2.3

Multiple Sample Test Tests involving more than 3 stimuli are classified as multiple sample tests. They may have equal (symmetrical) or unequal (asymmetrical) numbers of each stimulus. When they are applied as true difference tests, the judge is required to separate the samples into two groups or like samples. When they are applied as


11

directional tests, the judge is asked to identity the groups of higher or lower intensity or a given criterion. Difference test designs involving more than three stimuli have had only limited use. The limitation is based on the increase in psychological complexity and physiological fatigue which accompanies an increase in the number of stimuli. In addition, large quantities of samples are required and more time is needed for observer to make a decision, these tests appear to be most applicable to visual discrimination, where the judge does not rely on memory and fatigue is almost nonexistent. 2.4

Dual Standard Test The dual standards method was proposed for use in quality control situations. The subject is served four products; two are identified as references A and B and two are coded. The subjects must match the reference product with the coded product. The designation of the two references could reflect quality control limits or current production and product outside the limit. 2.5

Multiple Standards Test This test was developed for odour evaluation when a non-uniform standard was to be compared with an unknown. Any numbers of the questionable standards are presented simultaneously with the unknown and the subject is asked to designate the one which is most different. The chance probability of identifying the unknown correctly is ones over the total number of samples involved. The literature provides a somewhat conflicting selection of conclusions regarding the sensitivity of the various test methods; some sensory professionals suggest that the triangle is more sensitive than the duo-trio and the paired tests, while others have arrived at contrary conclusions. The various difference tests can be ranked in terms of increasing sensitivity as: paired, dual standard, duo-trio, triangle and multiple standard (Amerine et al, 1965). Recently Stone and Sidel (1993) have concluded that all discrimination tests are equally sensitive. 3.0

DESCRIPTIVE ANALYSIS

Descriptive analysis is a sensory methodology that provides quantitative descriptions of products based on the perceptions of a group of qualified subjects. It is a total sensory description taking into account all sensations that are perceived – visual, auditory, olfactory, kinaesthetic and so on- when the product is evaluated. Descriptive analysis results provide complete sensory descriptions of an array of products and provide a basis for determining those sensory attributes that are important to acceptance. The results enable one to relate specific process variables to specific changes in some of the sensory attributes of a product. From the product development view point, descriptive information is essential in finding out those product variables that are different and from which one can establish cause and effect relationships.


12

A descriptive test involves relatively few subjects who have been screened. Screening should be product category specific as is the subsequent training effort. Training is primarily focused on development of descriptive language which is used as a basis for scoring the product. Apart from this the other important activities that are part of training include the grouping of attributes by modality (i.e. appearance attributes, aroma attributes and so on), listening them by occurrence, developing a definition for each attribute, identifying helpful references for use during training, and familiarizing the subjects with the scoring procedure. There are numerous applications for descriptive analysis, including monitoring competition, storage stability / shelf life, product development, quality control, physical / chemical and sensory correlation, etc. Depending up on the test methods used the training can be quite different. Some of the descriptive methods described in the literature are summarized here. 3.1

Flavour Profile

The flavor profile method is the only formal qualitative descriptive procedure and is probably the most well known of sensory test methods. This utilizes a panel of four to six screened subjects who first examine and then discuss the product in an open session. Once agreement is reached on the description of the product the panel leader summarizes the results in report form. The method has considerable appeal because results could be obtained rapidly and would obviate the need for statistics. 3.2

Texture Profile

This method represents advancement in descriptive analysis with respect to development of the descriptive terminology, the scales for recording intensities and the word/product anchors for each scale category. In developing the method, the objective was to eliminate problems of subject variability, allow direct comparison of results with known materials and provide a relationship with instrument measures. There is considerable appeal to the direct link between specific instrumental measures of these rheological properties of a product and the responses of a panel of specific sensory attributes, for example, texturometer units and hardness sensory ratings. However, separation of texture from other sensory properties of a product such as colour, aroma, tests and so forth limits the total perception of the product’s sensory properties.

3.3

Quantitative Descriptive Analysis

The quantitative descriptive analysis (QDA) method was developed with an approach that was primarily behavioural in orientation with a consensus approach to language development, use of replication for assessing subject and attribute sensitivity, and for identifying specific product differences and defined statistical analysis. The development of method evolved from a number of considerations to ensure that it would:


13

• • • • • • •

Be responsive to all the sensory properties of a product Rely on a limited number of subjects for each test Use subjects qualified before participation Be able to evaluate multiple product in individual booths Use a language development process free from leader influence Be quantitative and use a repeated trials design Have a useful data analysis system

In a QDA test, the subjects evaluate all of the products on an attribute by attribute basis on more than a single occasion. 4.0

OTHER METHODS

Many more descriptive methods have been described in the literature which is more or less on the lines of the test methods discussed above. The spectrum descriptive analysis, for example, involves extensive training activities, reflecting the basic flavor and texture profile procedures, with particular reliance on training the subjects with specific standards of specified intensities. Free choice profiling is another approach in which no subject screening or training are required and the subject can use any words they want to describe the products being evaluated. The time advantage may, however, actually not be there since the experimenter requires spending time explaining the testing procedures to the subjects. 4.1

Scoring

The most frequently used of all sensory testing systems is scoring because of its diversity, apparent simplicity and ease of statistical analysis. Scoring methods have most extensively been used by the dairy industry for product development and improvements, shelf life studies and assessing suitability of packaging materials. Score cards based on 100 points generally used for judging and grading of dairy products. Most recently 25 points score cards have been suggested (Bodyfelt, et al, 1988). It is believed that numerical rating tests give more complete information than either ranking tests or descriptive rating tests, but the judges must be trained. Since there is no indication of liking to the test product, palatability norms should be established. The score card must be properly developed giving due weightage to all the sensory attributes. 4.2

Ranking

Ranking tests require that judges arrange a series of two or more samples in an ascending or descending order of intensity of a specific attribute. In ranking test for quality, the usual objective is to select one or two if the best samples rather than to test all samples thoroughly. Ranking is often used for screening inferior from superior experimental samples in product development and occasionally in training judges. Samples may be ranked in order of degree of acceptability or in order of general quality, or by specific attributes of colour, volume, texture or flavour intensity. Judges should be thoroughly familiar with all aspects of the sample Sensory and Related Techniques for Evaluation of Dairy Foods

14

characterization under consideration. This may not be easily achieved in practice, because stimuli may vary along several dimensions simultaneously, complicating the interpretation of the criteria used to differentiate. This problem arises not only in ranking tests but in most methods. 5.0

AFFECTIVE/ACCPTANCE TESTING

Acceptance testing, a valuable and necessary component of every sensory programme is performed at consumer’s levels. It refers to measuring liking or preference for a product. Preference can be measured directly by comparison of two or more products with each other, that is, which one of the two or more products is scored significantly higher than another product in a multiproduct test, or which product is scored higher than another by significantly more people. The two methods most frequently used to directly measure preference and acceptance are the paired comparison test and the nine point hedonic scale. Other methods are either modifications of these two methods or are types of quality scales: for example, excellent to poor and palatable to unpalatable. 5.1

Hedonic Scale

The nine point hedonic scale has been used extensively since its development with a wide variety of products and with considerable success. The scale is easily understood by naïve consumers with minimal instruction and the product differences are reproducible with different groups of subjects. The results from use of this scale are most informative since computations will yield means, variance measures and frequency distributions, all by order of presentation and magnitude of difference between products by subject and by panel and the data can be converted to ranks as well, which yields product preferences. As an example of the scale is given below: Like extremely Like very much Like moderately Like slightly Neither liked nor disliked Dislike slightly Dislike moderately Dislike very much Dislike extremely

: : : : : : : : :

9 8 7 6 5 4 3 2 1

The sensory acceptance test is a very cost-effective resource that has a major role to play in the development of successful product. Properly used, it can have a significant impact on the growth and long term development of sensory evaluation. 5.2

Consumer evaluation

With the increase in competition, availability of many brands of same product in the market and the choice of consumers, it is highly desirable for the food/dairy industry to study the acceptance/preference and needs of consumers. In some cases it


15

is possible to create markets for certain dairy products when none existed earlier. In many other situations, such as alterations in existing formulations, change in packaging materials, use of some additives or adoption of a new technology, the food processor has to go to consumers with their product to study their acceptance/preference. While conducting the consumer studies, the sensory leader/organizer should consider all the factors that are important in achieving the desired results. Some of these factors are: clear objectives, target population, start and completion dates, representative test samples, number of products number of responses per sampling, sample coding procedures, questionnaire, instruction on serving and pre-screening, data analysis and processing procedure, and proposed reporting schedule. As far as preference and acceptance of consumers is concerned the factors are grouped into two categories viz. 1) the attitude of the dairy product and 2) of the consumer. Attitude of the Dairy Product: This is related to the product itself in respect of availability; utility; convenience; price; storage stability/ requirements; safety and nutritional value; and sensory properties, which of course is very important. Attitude of the Consumer: Religion preference; nationality and race; age and sex; education, socio-economics; psychological motivation such as symbolism of food, advertising, etc. and physiological motivation, such as thirst, hunger, deficiencies and pathological conditions. While designing consumer studies and interpreting the results, the role of above factors may be considered. Questionnaire for Consumer Studies: A well developed questionnaire for obtaining desired information, including preference, from the consumers is very important. The important considerations for developing a questionnaire are that it should be: • • • •

simple and clear realistic use appropriate terms avoid stereotype answers

One example of such a questionnaire for seeking consumer opinion on Control milk sample (A) and on experimental milk sample fortified with Vit A. (B) is given below: 1.

Prefer sample A……………. Prefer sample B …………….

2.

Why do you prefer the sample of your choice (Tick mark one or more): Preferred milk sample has Richer taste ……………. Sweeter taste …………….


16

Smoother body ……………. Rich consistency ……………. Other ……………. 3.

If you prefer to buy the preferred sample, how much more (if any) per litre would you be willing to pay: 25 paise ……………. 50 paise ……………. Re. 1 ……………. None …………….

The above questionnaire shows the relationship between preference for milk and willingness to pay more for the preferred sample. 6.0

REFERENCES

Amerine, M. A., Pangborn, R. M. and Roessler, E. B. (1965). Principles of Sensory Evaluation of Food, Academic Press, New York. ASTM (1986). Manual on Sensory Testing Methods. STP 434, American Society for Testing and Materials, Philadelphia, U.S.A. Bodyfelt, F. W., Tobias, J. and Trout, G. M. (1988). The Sensory Evaluation of Dairy Products, AVI Publishing Co. New York. Dharam Pal, Sachdeva, S. and Singh, S. (1995). Methods for determination of sensory quality of foods: A critical appraisal. J. Fd. Sci. Technol. 32 (5):357-367. Stone, H. and Sidel, J. (1993). Sensory Evaluation Practices, Academic Press Inc. London.


17

SENSORY EVALUATION OF MILK

Dr. Ashish Kumar Singh Senior Scientist Dairy Technology Division NDRI, Karnal 1. INTRODUCTION The sensory evaluation of milk is of utmost importance. Packaged and retail sale of fresh milk comprises a major share of Indian Dairy industry (both in the organized and unorganized sectors). Since fluid milk is consumed by most everyone everyday it is being assessed dairy for its quality. If the flavour of milk is not appealing or appetizing less of it will be consumed. The sensory characteristics of any dairy product are dependent on the quality attributes of milk ingredients used. FINISHED MILK PRODUCTS CAN NOT BE BETTER THAN THE INGREDIENTS FROM WHICH THEY ARE MADE. If the raw milk supply is properly assessed for its sensory quality all off-flavour defects due to raw milk could be minimized if not eliminated. Among dairy product judges the scoring or differentiation of milk into different quality classes demands keener, more fully developed senses of smell and taste than in the sensory evaluation of other dairy products. Many of the off-flavours present in fluid milk are more delicate, less volatile or more elusive than those present in other milk products. Milk, may be raw or pasteurized, skim or whole, toned or double toned, standardized or full fat, cow or buffalo. For the purpose of present discussion, milk would mean PASTEURIZED, STANDARDIZED (MIXED) MILK unless otherwise specified. Pasteurization is effected by heating the milk to 72oC for 15 sec or 63oC for 30 min in HTST or LTLT respectively. Pasteurized milk commonly possesses some degree of a heated or cooked flavour especially immediately after processing, but the intensity of cooked flavour diminishes during storage. The flavour of milk is affected by: a. heating-up and cooling time. b. temperature difference between the product and heating medium c. velocity of the product in a continuous system


18

d. occurrence of product ‘burn on’ and e. direct Vs indirect heating methods. The flavour of pasteurized unhomogenized milk undergoes flavour changes during storage as below: HEATED--> NORMAL--> FLAT--> METALLIC--> OXIDISED The extent of flavour deterioration depends on the storage time, session of the year, type of roughage fed to the cow and buffaloes and relative levels of cupric or ferric ions. 2. MILK SCORE CARD The original score card (100 point scale) developed by the ADSA has been extensively modified and is presented on the next page. Bacterial counts, milk temperature and sedimentation test are important data to be provided by lab. Evaluation of the container/closure is also a valid quantity criterion that should be evaluated when required. Flavour on the new score card is evaluated on a 10-point scale. 100 point score card can still be used provided the milk has a bacterial content of 20,000 ml and a maximum temperature of 7.2oC. Familiarity with the score and use of scorecard guide is important for milk product judging.

SCORE CARD FOR MILK Product _______________

Date__________

------------------------------------------------------------------------------------------------Sample number FLAVOUR

NO CRITICISM 10 NORMAL RANGE 1-10 UNSALEABLE

10

Criticism acid astringent barmy bitter cooked cowy feed fermented/fruity flat foreign garlic/ onion lacks freshness malty oxidized light-induced oxidized metal induced rancid


1

2

3

4

Score

19

salty unclean -----------------------------------------------------------------------------------------------------------SEDIMENT 3 -----------------------------------------------------------------------------------------------------PACKAGE 5 -----------------------------------------------------------------------------------------------------dented/defective NO CRITICISM

dirty inside/outside

5

leaky/not full

NORMAL RANGE

heat seal defective

1-5

illegible printing

UNSALEABLE

labeling/code incorrect

0 -----------------------------------------------------------------------------------------------------BACTERIA 5 ------------------------------------------------------------------------------------------------------TEMPERATURE 2 ------------------------------------------------------------------------------------------------------TOTAL SCORE Signature of the judge Fig. 1 The modified ADSA scorecard for milk

3. JUDGING OF MILK & MILK PRODUCTS Table 1. Suggested scoring guide for flavour for milk Intensity of flavour defect Moderate

Definite

Strong

Slight

Pronounced

Astringent

8

7

6

-

-

Barmy

5

4

3

2

1-0


20

Bitter

5

4

3

2

1-0

Cooked

9

8

7

6

5-0

Cowy

6

5

4

3

2-0

Feed

9

8

7

6

5-0

Fermented/fruity

3

2

1

0

0

Flat

9

8

7

-

-

Foreign

3

2

1

0

0

Garlic / onion

5

4

3

2

1-0

High acid

3

2

1

0

0

Lacks freshness

8

7

6

0

0

Malty

5

4

3

2

1-0

Metallic

5

4

3

2

1-0

Light induced

6

5

4

3

2-0

Metal induced

5

4

3

2

1-0

Rancid

4

3

2

1

0

Salty

8

7

6

2

4-0

Unclean

3

2

1

0

0

Oxidized

3. SOME MILK SCORING TECHNIQUES 3.1 Preparation of samples for evaluation This depends on the purpose or objectives of evaluation, number of participants and the quality criteria to be assessed. If several persons are to judge the milk samples for flavour, container and closure, sediment and other criteria then several containers of each individual lot of milk must be provided. The sediment test/bacterial count of each sample should be provided. 3.2 Order of examination and scoring 3.2.1 Sediment test


21

It should be performed first. The kind, amount and size of sediment particles should be carefully observed and scored against a chart or mental image. 3.2.2 Closure Closure should be carefully observed. Now a days bottles or cartons (not used in India) are not the usual packaging material. The milk is being packaged polyethylene sachets. Hence the evaluator must see that the packaging properly sealed to prevent leakage/pilferage. 3.2.3 Container Container as stated above, since plastic bags is now in vogue; these should be examined for extent of fullness, cleanliness and freedom from cuts/nicks/pinholes from leakage. 3.2.4 Flavour The milk should be properly tempered between 13 to 18oC preferably 15.5oC. Milk samples should be poured into clean, odourless glasses or paper/plastic cups. 10 to 15 ml milk should be poured and a sip taken, rolled around the mouth and flavour sensation noted and then expectorated. Sometimes, any aftertaste may be enhanced by drawing a breath of fresh air very slowly through the mouth and then exhaling through the nose slowly. A full WHITE of air should be taken soon after the sample is placed in the container for any off-odour that may be present. 3.3 Evaluation temperature Pasteurized milk should at 7.2oC but lower than 4.4oC is preferred. A 2-point scale may be used. If the temperature is above 7.2oC the sample may be scored ZERO. Samples at 4.4oC or below should be scored a perfect or 2 score. 3.4 Evaluation of sediment Consumers want that the milk should be free from foreign matter. A 3-point scale may be employed. Presence of any sediment is serious and should receive a ZERO score. One Possible scoring system could be:

No sediment

3

< 0.02 mg/disc

2

0.025mg/disc

1

>0.025mg/disc

0

3.5 Evaluation of milk flavour


22

Typically the flavour of milk should be PLEASANTLY SWEET AND POSSESS NEITHER A FORETASTE NOR AN AFTERTASTE other then that imparted by the natural richness due to milk fat and milk solids. When milk clearly exhibits the soc-called TASTE there is usually something WRONG with the flavour of the milk sample. Thus milk is considered to have a defect if it has an odour, fore-or after-taste and does not leave the mouth in clean, sweet, pleasant condition, following tasting. The scoring guide lists more frequently observed off-flavours. The defects should be described while scoring. 4. UNDESIREABLE FLAVOURS 4.1 Acid Sour detected by taste and smell-due to microbial conversion of lactose to lactic acid, which imparts a tingling effect. 4.2 Astringent Not common in milk. 4.3 Barny Transmitted off-flavour due to poor ventilation, foul smelling environment. Perceived by sniffling and tasting. Characteristic aftertaste. 4.4 Bitter Associated with other defects like astringency, rancidity due to weeds and microbial growth specially psychrotrophs.. 4.5 Cooked Heat-induced defect appears when milk is heated to 76oC or more. There are 4 types of heat induced flavours: COOKED/SULPHUROUS; HEATED OR RICH; CARAMELISED and SCORCHED Heated and cooked flavors are easily identified, reaction time is quick, and sensation remains after expectoration. Cooked flavour may also be noted through smell. 4.6 Cowy (acetone) Distinct, persistent unpleasant, medicinal chemical aftertaste with acetone bodies in milk i.e. ketosis in cows. 4.7 Feed Imparts aromatic taints to milk when fed ½-3 hours prior to milking. The offflavour is aromatic sometimes pleasant (e.g. alfa-alfa), detected by smell varies with feed. To prevent such feeds should not be fed 3 hours prior to milking. 4.8 Fermented/Fruity Due to microbes, resembles vinegar, pineapple, apple. Found in old pasteurized milk, due to growth of Pseudomonas sp. (P. fragii).


23

4.9 Flat Flat taste/mouthfeel—lack of richness. 4.10 Foreign Smelled or tasted, due to chemicals/detergents, disinfectants, sanitizers, exposure to fumes of petrol, diesel, kerosene, insecticides, ointments, medication to cows etc. 4.11 Garlic/onion (weedy) Pungent odour and persistent aftertaste. 4.12 Lacks freshness (stale) Taste reaction indicates loss of fine pleasing taste. Slightly chalky. May be ‘forerunner’ of either oxidized or rancid off-flavour or off-flavour caused by pshychrotrophs. 4.13 Malty Flavour definite or pronounced, suggestive of malt caused by the growth of S lactis var. Maltigenes at > 18.2oC for 2-3 hours can be smelled or tasted. Bacterial population in millions, followed by acid/sour taste. 4.14 Metal-induced oxidized off-flavour Due to lipid oxidation-metal catalyzed. Metallic, oily, cardboardy, cappy, stale, tallowy, painty and fishy are used to describe this off-flavour. The off-flavour is quickly perceived in the mouth and has a relatively short adaptation time. 4.15 Light-induced oxidized off-flavour Described as burnt, burnt protein, burnt feathers, cabbagy, medicinal or chemical-like, light-activated or sunlight flavour or sunshine flavour, light catalyzed lipid oxidation as well as protein degradation both are involved. It requires riboflavin that is naturally present in milk. Homogenized milk is more susceptible but is resistant to oxidized off-flavour (due to lipid oxidation) the opposite is true for nonhomogenized milk. 4.16 Rancid Extremely unpleasant, due to volatile fatty acids formed through enzymatic hydrolysis of fat. Soapy, bitter and unclean aftertaste. Flavour is nauseating and revolting. 4.17 Salty Perceived quickly in the mouth 4.18 Unclean Due to growth/activity of psychrotrophs at 7.2oC


24

SENSORY CHARACTERISTICS OF FRESH CHEESE

Dr. S. K. Kanawjia, Sanjeev Kumar** and Hitesh Gahane* Principal Scientist, Division of Dairy Technology NDRI, Karnal **Ph.D. Scholar and * M.Tech (DT)

1. Introduction

Cheese, the nature’s wonder food and the classical product of biotechnology, is highly nutritious food with good keeping quality, enriched pre-digested protein with fat, calcium, phosphorus, riboflavin and other vitamins, available in a concentrated form. It is the most important category of fermented foods, has been reported to have therapeutic, anticholesterolemic, anticarcinogenic and anticariogenic properties beyond their basic nutritive value. They, contributing to a variety in our gustative desire, have been recognized to provide important nutrients and considered superior over non-fermented dairy products in terms of nutritional attributes as the micro flora present produce simple compounds like lactic acid, amino acids and free fatty acids that are easily assimilable. Some of the cheese flora has been reported to inhibit the growth of certain toxin-producing bacteria in the intestine. Soft unripened cheeses are commonly known as “Fresh Cheese” and are made by coagulating either whole milk, partly skimmed milk, skim milk or cream; eliminating a large part of the liquid portion (whey) and retaining the coagulated milk solids. The amount of water retained in the curd greatly influences the relative softness of unripened cheese made from milk having constant casein-to-fat ratio. Softness of cheese also depends on the extent of protein hydrolysis salt content and the amount of milk fat in cheese. Soft unripened cheese derive their flavour mainly from the culture and the cream dressing. Cottage cheese, Cream cheese, Mozzarella cheese, Ricotta cheese, paneer etc are some of the common varieties of fresh cheese. They differ from each other in their method of manufacture with respect to type of milk, treatment given to milk, type of culture, amount of culture method of coagulation, cutting of curd, cooking of curd, pressing of curd etc. Consequently, they differ in sensory as well as chemical attributes. The desirable sensory attributes of fresh cheeses, defects and their probable causes and remedies with special reference to cottage cheese are described in this lecture note. 2. Scenario of Cheese Production in India Scenario of cheese production in India is quite bright because of the facts that cheese has all the beneficial attributes of an ideal dairy product and the emergence of


25

new global economic reforms based on globalization and liberalization in the marketing arena that has unfastened the door to the Indian dairy industry to penetrate the international cheese market. There has been a steady increase in the consumption of cheese in most countries worldwide, the annual growth rate in cheese consumption being over 3 per cent with an acceleration being expected due to worldwide trend of adopting “Western” consumption habits with a high level of cheese in the diet list. In India cheese, production has been accelerating quite steadily, being 1000 tonnes in 1980 to 40000 tonnes in 2007, against the world production of 16 million tonnes. Till about 8-10 years back, the only major regional/national players in the cheese market were Amul, Verka, and Vijaya – all from the cooperative sector. These plants are continuing to expand their cheese manufacturing capacities slowly in tune with the demand growth for cheese. Many new players like Dynamix and Dabur, and entrepreneurs, such as Vadilal, Vintage, Chaudhary’s Miraj, Kodai, etc have ventured in cheese production in recent years. At present Amul has targeted opening of 3000 Pizza retail franchise outlets all over the country by the year-end, which would boost the annual sets of Mozzarella cheese to 5000 tonnes. 3. Cottage Cheese Cottage cheese is a fresh, soft, unripened cheese made from sweet, pasteurized skim milk by lactic culture with or without the addition of rennet. The curd is cut and cooked to facilitate whey expulsion and development of proper curd consistency. When the curd has attained the desired consistency, whey is drained off, curd is washed and salted. Subsequently, the curd is dressed with cream in the case of creamed cottage cheese which contains 4% fat. Cottage cheese contains 80% moisture. 3.1 Desired sensory attributes 3.1.1 Appearance and colour The curd particles of cottage cheese should be distinctly separate and uniform in size and shape. The cheese should possess moderately glossy sheen and creamy white colour. The cream dressing should be reasonably viscous and foam free, and bulk of it should adhere to the curd particles. The excess dressing should form only a uniform and smooth coating on the curd particles. Free cream, free whey, lack of uniformity and the presence of lumps or curd dust are considered as common appearance defects in cottage cheese caused mostly by faulty method of manufacture viz., excessive cooking, insufficient washing, cutting of curd at too high or too low pH, rapid cooking, uneven cutting or cutting with a faulty knife or aggressive stirring low TS milk, excessive heat treatment of skim milk, use of excessive coagulator, severe stirring or orugh handling of curd during cooking etc. Appropriate corrective measures during manufacture of cottage cheese eliminate these defects.


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3.1.2 Body and texture of cottage cheese Ideally, creamed cottage cheese should have a tender body, and smooth and meat like texture. Curd particles should maintain their shape and individual identity but should not be too firm, rubbery or too soft. Smooth, meaty and tender curd particles exhibit good capillary desired for complete absorption of cream dressing common body & texture defects are listed below: 3.1.2.1 Too firm body: Firm or rubbery bodied curd particles of cottage cheese resist crushing between tongue and roof of the mouth. This defect occurs due to over use of rennet or other milk coagulator; cooking of curd at too high temperature and for too long; or cutting of curd at a pH more than 4.7 3.1.2.2 Mealy/Grainy/Gritty: Presence of this defect gives a corn meal like sensation in the mouth when masticated curd is pressed by the tongue against the roof. Also, a dry rough and serrated curd mass is observed when the washed curd particles of creamed cottage cheese are kneaded and smeared between the forefinger and thumb. The defect may be caused by overdeveloping the acid during curd formation; retention of too low moisture, non-uniform cutting of coagulum, uneven heating, too rapid cooking, inadequate stirring, and curd particles coming in contact milk extremely hot surfaces during cooking. 3.1.2.3 Gelatinous: Gelatinous cheese has a jelly-like and sticky character. Often this defect is associated with a bitter flavour and translucent appearance. This defect is caused by psychotropic bacteria. 3.1.2.4 Weak/soft/mushy: This defect is characteristic of high moisture, low-solid cottage cheese. It is caused by faulty manufacturing methods, which favour retention of whey in the curd. On storage such cheese may become pasty and bitter. 3.1.2.5 Over stabilized dressing: When this defect occurs the creamed cottage cheese appears dry and some individual curd particles are surrounded by a thick, pasty, coating. This usually happens due to the use of excessive amount of non-fat dry milk, stabilizers and/or emulsifiers.


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3.1.3 Flavour: Cottage cheese should have a fresh, clean, pleasant delicate (balanced culture) flavour that cleans up well immediately after the sample has been eliminated from the mouth. This flavor is made up of characteristic curd flavour and its acidity, volatile products by lactic acid organisms. Addition of cream and salt enhance the flavour of creamed cottage cheese. The probable cottage cheese being high perishable product is proving to the development of specific flavour defects as discussed below: 3.1.3.1 Acid/high acid/sour: Acid taste is clean and sharp while sour taste is pronounced and may be associated with other bacterial defects like fruity, fermented etc. Excessive acid development and/or insufficient washings of the curd cause this defect. Such product is sometimes also criticized for flavour defect like “whey taint”. 3.1.3.2 Bitter: Bitter flavour is characterized by its relatively slow reaction time; taste at or near the back of the tongue only; freedom from astringency; and persistence after expectorating the sample. The defect is most frequently encountered in old cottage cheese or in the sample stored at a temperature favourable for the growth of Pseudomonas organisms. 3.1.3.3 Flat: Absence of characteristic flavour or aroma is termed as flat flavour. A dry, unsalted and washed rennet curd yields a distinctly flat taste during the intermediary stages of oxidized flavour development. 3.1.3.4 Lacks freshness: The flavour of cottage cheese is its best immediately after manufacture. Cottage cheese progressively deteriorates in flavour during storage. Often this defect is referred as storage flavour because the aroma of cheese is similar to that of the refrigerator in which it was stored. 3.1.3.5 Fruity/Fermented: This defect is characterized by the presence of a pleasant aromatic flavour suggestive of pine apple, apple, banana or strawberry and distinctive lingering aftertaste. The cottage cheese stored at elevated or favourable temperatures for the psychrotrophic bacteria may develop this defect.


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3.1.3.6 Yeasty: Yeasty and vinegar like flavours have a peculiar aromatic quality in addition to high acidity. Yeasts and various other contaminants including psychrotrophic bacteria are generally responsible for causing this flavour defect. Other flavour defects in cottage cheese include malty, musty, oxidized, rancid, salty and unclean flavours. 4. Cream Cheese Cream cheese is a soft, unripened cheese made by coagulating cream (12-30% milk fat) either by lactic acid bacteria aided by milk coagulating enzymes or by direct acidification followed by removal of whey by centrifugation or pressing the curd in cloth bags. The fat content in the final product varies from 3 to 40%. Neufchatel cheese is a similar product made from whole milk of high fat contents. It contains about 20-25% fat. 4.1 Desirable sensory attributes 4.1.1 Flavour: Cream cheese should have a full rich, clean and milk acidic flavour. Neufchatel type cheese may have a moderate acid taste. More common flavour defects in various types of cream cheese may be flat, sour or too high acid, metallic, yeasty and unclean after taste. 4.1.2 Body and texture: Soft yet sufficiently firm body to retain its shape is the characteristic of cream cheese. The texture should be somewhat buttery and silky smooth. It should possess both spreading as well as slicing characteristics. Cream cheese prepared from cream containing 16% fat exhibits most desirable body and texture properties. In such cheeses the moisture and fact content may vary in the ranges of 50-54% and 37-42%, respectively. Cream containing less fat yields a cream cheese which is criticized as having grainy texture and crumbly body. Increased fat content of cream (20%) results in excessive smoothness and stickiness. Other body and texture defects of cream cheese include coarse, grainy, too firm and too soft. 5. Mozzarella Cheese It is a soft unripened variety of cheese of Italian origin. It is produced from whole or partly skimmed milk to which small amounts of starter or organic acids are added, followed by rennet extract. The curd is cut, allowed to firm up in the warm whey with occasional stirring and the whey is drained off. When the curd has developed the desired plasticity and fibrous texture and the whey acidity 0.65-0.70% LA, it is milded. The curd pieces are immersed in hot water kneaded, stretched and


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moulded. Salting of cheese is done by dipping the cheese in brine solution for few days. The cheese can be consumed after the brine treatment is complete. 5.1 Desirable sensory attributes 5.1.1 Colour and appearance: Mozzarella cheese should have a uniform white to light cream color. Faulty manufacturing method and microbial contamination may sometimes cause colour defects in the product. Use of too high salt may cause discoloration. Development of browning may be caused by using starter culture containing only Thermophilus. Contamination with Psuedomonas spp. Causes development of superficial reddish marks. 5.1.2 Body and Texture: Mozzarella cheese should have a soft, elastic, waxy and moist body with typical structure of pulled curd cheese. It should have a fibrous texture with no gas holes. It should possess a good slicing as well as melting properties. Use of too high salt or growth of Lactobacillus casei may cause poor melting quality. Undesirable microbial contamination may cause development of defects, like pigmentation, hole formation and other textural defects. Rapid evaporation of moisture from the surface leads to the development of granular texture. 5.1.3 Flavour: Bland, pleasant but mildly acidic with slightly salty taste is the characteristic of mozzarella cheese. Buffalo milk cheese is a more piquant and aromatic than cow milk cheese. Microbial contamination, particularly with Pseudomonas species may lead to the development of flavour defects like putrid smell, bitter flavour etc. Other flavour defects may be of absorbed or chemical nature as in the case of cottage cheese. 6. Ricotta Cheese It is yet another variety of soft unripened cheese of Italian origin. In the manufacture of ricotta cheese, mixture of whey and skim milk is acidified to a critical pH with lactic acid, acetic acid or acid whey powder and then heated. The resulting curd is recovered and over filled in perforated tin containers, cooled and allowed to drain free whey. Cheese is now ready for consumption. Ricotta cheese made from whole milk is consumed directly while made from skim milk or whey skim milk mixture is highly suited for pastry manufacture. Ricotta cheese from whole milk resembles highly creamed, cottage cheese but has a softer and more fragile texture. A mixture of skim milk whey yields a firmer and drier product which lacks its distinctive nutty flavour. In general ricotta cheese is soft, and creamy with a delicate, pleasant and slight caramel flavour.


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Ricotta cheese is highly susceptible to spoilage due to microbial contamination leading to flavour defects like sour, fermented, fruity etc. Excessive gas formation may also cause blowing of the lid of the container. 7. Paneer Paneer is an indigenous milk product made by coagulating heated milk preferably buffalo milk (6% fat) acid solution and/or sour whey. The whey is drained and the curd filled in hoops and pressed. The pressure is removed after 10-15 and the paneer is cut into pieces and immersed in chilled water for cooling. 7.1 Desirable sensory characteristics 7.1.1 Colour and appearance: Paneer should have uniform white colour with greenish tinge if made from buffalo milk and light yellow it prepared from cow milk. Paneer may develop colour and appearance defects as listed below: 7.1.1.1 Dull: This defect is recognized by its dead, unattractive appearance and suggest lack of cleanliness in manufacture. 7.1.1.2 Dry surface: Use of milk containing excessive amount of fat gives paneer with dry surface and unattractive appearance. 7.1.1.3 Surface skin: Exposure of paneer while hot to the atmosphere causes rapid evaporation of moisture from the surface resulting into the formation an undesirable yellow skin on the surface. 7.1.1.4 Visible dirt/ Foreign Matter: This defect may occur due to improper straining of milk, use of dirty water, dirty, windy surrounding, poor packaging and careless handling of paneer. 7.1.1.5 Mouldy surface: Long storage of product in humid atmosphere coupled with higher moisture content flavours development of moulds on the paneer surface. 7.1.2 Body and texture The body of paneer should neither be too firm nor too soft. It should remain retain its shape. The texture of the high grade paneer should be compact, smooth elastic and velvety. Paneer develops body and texture defects due to faulty manufacturing methods and microbial contamination. Excessive retention of moisture due to low coagulation temperature, delayed straining or incorrect pH of coagulation often gives a paneer


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with soft body and pasty texture. Low moisture content in paneer caused by higher coagulation temperature, incorrect pH at coagulation, use of low fat milk, yield hard and rubbery bodied paneer. Such paneer may also have a mealy texture. Frozen storage of paneer causes crumbly body and coarse/mealy texture in paneer. 7.1.3 Flavour Flavour of paneer is a characteristic blend of the flavour of heated milk curt, and acid. The flavour of the high-grade paneer should be pleasant, mildly acidic, slight sweet and nutty. Common flavour defects observed in paneer are similar to those as observed in other fresh cheese and can be eliminated by following proper manufacturing, method, sanitation, packaging, storage and handling. 8. References Bodyfelt, F.W.; Tobias, J. and Trout, G.M. 1988. The Sensory Evaluation of Dairy Products. Van Nostrand Reinhold, NY. Dharam Pal and Gupta, S.K. 1985. Sensory evaluation of Indian Milk Products. Indian Dairyman, 37: 465 Kanawjia, S.K. and Singh, S. 1996. Sensory and Textural changes in Paneer during storage. Buffalo J. (Thailand) 12: 329-32 Khurana, H. and Kanawjia S. K. 2007. Recent trends in fermented milks. Current Nutrition Food Sci. (USA) 3: 91-108 Makkal, S. and Kanawjia S. K. 2003. Preservation of Cottage Cheese: A review Indian J. Dairy Sci. 56: 1-12 Nelson, J.N. and Trout, G.M. 1964. Judging of Dairy Products. Olsen Publ. Co. Milwaukee. Wis., USA. Tiwari, B.D. 1996. Sensory attributes of fresh cheese. Compendium: Sensory evaluation and rheology of milk and milk products. CAS, DT Division, NDRI, Karnal: 52-57.


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SENSORY ATTRIBUTES OF ICE-CREAM

Dr. F.C. Garg Dairy Technology Division NDRI, Karnal

1. Introduction Ice cream is a delicious, wholesome nutritious frozen dairy food. It has evolved over a period spanning about five centuries. The great technological progress made in the field of dairying in the nineteenth century such as the development of centrifugal separator, mechanical refrigeration, better understanding of chemistry and bacteriology provided stimulus to the development of a large ice-cream industry that we see today. Ice cream has occupied a unique place in the diet of western people and is gaining steadily in popularity all over the world. For instance, the annual production of ice cream in USA has reached more than 3770 million litres. Other countries ranking high in annual production of Ice cream and related products are Japan: (750 million litres), Canada (476), Australia (331), and UK (218). India is the third largest producer of ice cream in the world with production of over 513 million litres annually. It has been estimated that 0.6 per cent of total milk production in our country is utilized for making ice cream and Kulfi. The ice cream industry in India is expanding very fast witnessing an estimated growth rate of 25 to 35 per cent per year. Production of excellent quality Ice cream is essential to the success and progress of the ice-cream industry. The quality of ice cream is judged by the consumer on the basis of its sensory attributes i.e. flavour, body and texture, melting behaviour, colour and the appearance of package or container. Besides, the product should also comply with legal standards with regard to its chemical composition and bacteriological quality. Ice cream not possessing desirable sensory properties cause diminished consumer goodwill, sales and income to the manufacturer. 2. Factors Affecting Sensory Attributes of Ice-cream The quality of ice cream depends not only on composition of ice-cream, but also on the quality of raw materials used, methods of manufacture, distribution and sale of the product – these factors are under the control of the ice cream maker. A full knowledge of the factors by which the quality may be attained or controlled is therefore, essential for the production of ice cream possessing desirable sensory attributes. There are many differing concepts of ‘perfect ice-cream’. Individual preferences can cause large variations in what people consider to be ice cream of highest quality. Some prefer ice cream with a low fat content, while others will want high fat. Some will like very smooth textured ice-cream, others may prefer it be not too smooth. Variations exist in the required sweetness level and so on. Therefore, Sensory and Related Techniques for Evaluation of Dairy Foods

33

desirable sensory attributes of ice cream can be best explained by giving details of defects and faults which may be found in ice cream, and show how these faults occur and how they may be overcome. 3. Judging of Ice-cream The available methods of determining the sensory attributes of ice cream rely mainly on tasting and using a scorecard. Such scorecards give maxima for various aspects of the ice-cream quality such as flavour, texture, body and colour. The American Dairy Association has stipulated a scorecard for ice cream, which carries a maximum score of 10 for flavour, 5 for body and 5 for colour and appearance, 3 for melting quality and 2 for bacterial content. The recommended scoring guide is given in Table 1. Table 1. The ADSA scoring guide for sensory defects of ice cream

Intensity of Defect ____________________________________________________________________ Criticisms

Slight

Definite

Pronounced

Flavour Acid (sour)

4

2

0

Cooked

9

7

5

Lacks flavoring

9

8

7

Too high

8

8

7

Unnatural

8

6

4

Lacks fine flavour

9

8

7

Lack freshness

8

7

6

Metallic

6

4

2

Old ingredient

6

4

2

Oxidized

6

4

1

Rancid

4

2

0

Salty

8

7

5

Storage

7

6

4

Flavouring:


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Sweetener: Lacks

9

8

7

Too high

9

8

7

Syrup Flavour

9

7

5

Whey

7

6

4

Coarse/Icy

4

2

1

Crumbly (brittle, friable)

4

3

2

Fluffy (foamy)

3

2

1

Gummy (pasty, sticky)

4

2

1

Sandy

2

1

0

Soggy (heavy, pudding-like)

4

3

2

Weak (watery)

4

2

1

Body and texture

Table 2. Flavour defects of ice-cream, their causes and remedies Defects A

High flavour

Cause Presence amount

of of

Prevention large Adding right amount of flavoring

flavouring material.

material B

Low flavour

Presence of insufficient Adding right amount of flavoring amount

of

flavouring material.

material C

Acid flavour

Presence of an excessive amount of lactic acid (developed)

D

Bitter flavour

Use of inferior products


¾ Using fresh dairy products ¾ Prompt, efficient cooling of mix ¾ Avoiding prolonged storage of mix at high storage temperature ¾ Using true flavour extract ¾ Avoiding use of dairy

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E

Cooked flavour

F

Flat flavour

¾ Overheating the mix. ¾ Using overheated concentrated dairy products Use

of

insufficient

flavour, sugar or milk

products stored for long period at low temperature ¾ Using products free from off flavour ¾ Carefully controlling pasteurization process ¾ Using conc. Products free of cooked flavour ¾ Using right amount of these ingredients

solids G

H

I

Metallic

Copper contamination

flavour

Bacterial action

Unnatural

Flavour not typical to ice

flavour

cream

Oxidized flavour

¾ Using oxidized flavoured dairy products. ¾ Metallic contamination.

¾ Avoiding copper contamination of mix during processing. ¾ Avoiding use of products have metal flavour. ¾ Using high quality flavouring products. ¾ Using high quality dairy and non-dairy products. ¾ Using fresh dairy products. ¾ Using only stainless steel equipment. ¾ Using antioxidants. ¾ Pasteurizing the mix at high temperatures.

When ice cream is being judged organoleptically it is important that the serving temperature should be correct. If it is too cold the palate will be deadened, and it will not be possible either to enjoy the ice cream or to judge any of its sensory characteristics. If it is too warm it will have melted partially judging of body and texture will be almost impossible. A consumer judges the quality or sensory attributes of ice cream on the basis of several characteristics – these are flavour, body, texture and appearance of the product and the package. 3.1 Flavour Ice cream is a mixture of fat, sugar and milk solids-not-fat together with added flavour and colour. An increase in total solids increases the richness of the ice cream and normally improves the flavour, texture and body. Some if these ingredients have marked flavour, others are more nearly neutral or bland. However, the flavour of no single ingredient should predominate, but each should blend together to form a


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harmonious whole, creamy sweet sensation with a slight flavour, leaving a pleasant after taste which must not be excessive. Many possible flavour defects may arise due to use of faulty ingredients. The more common flavour defects are given in Table 2. Table 3. Body and texture defects of ice cream Name A

Crumbly body

Causes

B

Soggy body

C

Shrunken body

(The ice cream shrinks away from the sides

and top of the container)

D

Weak body

E

Buttery texture

F

Coarse or ice texture

Prevention Low T.S. Content Insufficient Stabilizer Excessive overrun Improper homogenization Low overrun High sugar content Excessive amount of stabilizer

Increasing T.S. Content Increasing Stabilizer Decreasing overrun Proper homogenization

Proper overrun Optimum suggest content Right amount of stabilizer

Fluctuating temperatures during storage Excessive overrun Protein instability Rough transportation

Low T.S. content Insufficient stabilizer Improper homogenization High fat content Slow freezing Low T.S. content Insufficient stabilizer Slow freezing Slow hardening Insufficient ageing

Increasing T.S. content Increasing stabilizer

Proper homogenization Optimum fat content Fast freezing

Increasing T.S. content Increasing stabilizer Fast freezing Fast hardening Sufficient ageing Avoiding heat shocking Avoiding prolonged


Avoiding fluctuating temperature during storage Reducing overrun Avoiding high acidity in mix Avoiding rough transportation.

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G

Fluffy texture

H

Sandy texture

Heat shocking Prolonged storage Excessive overrun Low T.S. content High emulsifier content High M.S.N.F. (Lactose) content Fluctuating temp. in retail cabinets Long storage Period

storage

Decreasing overrun Increasing T.S. content Decreasing emulsifier content

Decreasing M.S.N.F. (Lactose) content Avoiding fluctuating temperatures in retail cabinets Reducing storage periods

3.2 Body and texture Both the body and texture of ice cream may be determined readily by the senses of sight and touch. The desired body in ice cream is that which is firm, has substance, responds readily to dipping and melts down at ordinary temperatures to a creamy consistency. The desired texture is that which is fine, smooth, velvety and carries the appearance of creaminess throughout. The possible body and texture defects which may be encountered in ice cream are presented in Table 3. 3.3 Melting Quality High quality ice cream should show little resistance toward melting when it is exposed to room temperature. During melting the mix should drain away as rapidly as it melts and form a smooth, uniform homogeneous liquid. Any variations from this behaviour may lead the consumer to be suspicious of its quality. The defects in melting quality frequently observed in judging ice cream are given in Table 4. Table 4. Melting quality defects of ice cream Name

Causes

Prevention

a)

Curdy meltdown

High acidity of mix.

Using fresh dairy products

b)

Slow melting

*Excessive amount of

* Reducing the amount of

stabilizer

stabilizer.

*Improper homogenization.

* Proper homogenization


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c)

Whey leakage

* Poor quality dairy

* Using fresh dairy products

products

* Balancing the mix

* Improperly balanced mix.

properly.

* Improperly stabilized mix. * Using more effective stabilizer d)

Foamy melt

* Excessive overrun.

* Reducing overrun

down

* Excessive amount of

* Reducing amount of

emulsifier.

emulsifier.

3.4 Colour The colour of the ice cream should be attractive and pleasing. The ideal colour is characteristic of the flavour, true in shade and neither too pale nor too intense. For example, vanilla ice cream should have a creamish yellow to white colour. Uniform, natural colour is desirable in ice cream. Excessive colour is the result of adding too much artificial colour to the mix. An uneven colour results if the colour is not properly added and also if care is not exercised when changing flavours. An unnatural colour is caused by (a) carelessness in adding the colour, (b) improper use of colours, or (c) use of foreign materials. 4. Conclusion Therefore, an excellent quality of Ice-cream can be made only from good mix ingredients properly balanced to produce a desirable composition along with proper processing, freezing, hardening and distribution, under proper sanitary conditions. All these factors are important and must be carefully controlled if the ice cream having desirable sensory attributes is to be produced. It must be remembered that product inferiority constitutes one of the greatest menaces to the success and progress of the ice cream industry. The consumer has learnt to depend upon Ice cram as a safe, enjoyable, energy-giving, nourishing and refreshing food. References Arbuckle, W.S. (1986) Ice cream, 4th Edn., Van Nostrand Reinhold Co. NY Bodyfelt, F.W., Tobias, J. and Trout G.M. (1988) The sensory evaluation of Dairy products. Van Nostrand Reinhold, NY. Hyde, K.A. and Rothwell, J. (1973) Ice cream. Churchull Livingstone, Edinburgh, UK.


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SENSORY EVALUATION OF DAIRY PRODUCTS WITH SPECIAL EMPHASIS ON FLAVOUR LEXICON

V. Pathak and Z. F. Bhat Associate Proffesor & Head Division of Livestock Products Technology F.V.Sc. & A.H., SKUAST-J Introduction:

Sensory evaluation of a food refers to its scientific evaluation through the application of human senses. It involves development and use of principles and methods for measuring human responses to products and ingredients. These principles and methods have broad application for a variety of products. The common element in these tasks is the use of humans as evaluators. It is this link, the human evaluator, that suggests sensory evaluation's proximity to, if not reliance on, the behavioral and social sciences. Sensory evaluation complies with the principles of science and is different from organoleptic evaluation as the results are often reproducible and comparable. This new field is founded principally on the behavioral and social sciences, rather than chemistry, microbiology, and engineering, the principal scientific fields in which traditional dairy scientists have been trained. Behavioral research in perception, learning, cognition, psychophysics, and psychometrics, to mention only a few, provides the basis for the principles and methods the sensory scientist uses today. One thing in common to all sensory assessment methods is that they use humans as the measuring instrument. Even though sophisticated and highly sensitive measuring instruments such as gas chromatographs, mass spectrometers, nuclear magnetic resonance spectrometers, IR and UV spectrophotometers, etc., are now available, the importance of sensory analysis has grown rather than diminished. The problem with instruments is that one instrument will analyse only single component at a time which does not fulfill our requirement as we are interested in getting total sensory impression of a processed food product at the same time. The dairy industry has come a long way since the early 1900s, when it began developing techniques for judging dairy products to stimulate interest and education in dairy science. Since then sensory analysis techniques have developed into powerful tools for understanding how the appearance, flavor and texture attributes of dairy products drive consumer preferences. In the traditional methods that emerged, judging and grading dairy products normally involved one or two trained “experts” assigning quality scores on the appearance, flavor and texture of the products based on the presence or absence of predetermined defects. Modern sensory techniques can help dairy processors develop new products that are highly appealing to consumers; enable processors to optimize a product’s flavor, texture and color to attract specific target audiences as well as accurately monitor product quality; can help determine variations in sensory attributes associated with processing variables, geographic region of production, production season, etc. Sensory and Related Techniques for Evaluation of Dairy Foods

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Anatomical Structures involved: Tongue: The four basic tastes are: sweet, salty, sour and bitter. The papillae for sweet are more concentrated on tip of tongue, the saline at tip and edge, the sour at the edge, and the bitter at the back. The papillae for bitter are especially deep, and so this sensation takes longer to perceive but tends to linger. Nose: We sense odour at the ‘Regio Olfactory’ (R) which lies at the top of the inside of the nose. The nose has two openings; the nostrils are anterior nares, the openings at back of throat are the posterior nares or choana. In ordinary breathing, the inspired air does not stream through the upper part of the nasal chamber. A definite sniff is required for air to reach this area and so this technique is called ‘sniffing’. The air whirls in the upper passage creating a multiplication effect. Skin: While tasting, we not only perceive the four basic tastes but also warmth, cold, pain, tactile and pressure sensations. These belong to the cutaneous senses. In contrast to the cutaneous senses, the kinesthetic sense is a muscle or power sense. It gives us a sensation of resistance. Ear: Sound sensations perceived while tasting, like crackly in the case of crisp cookies (biscuits) and crunchy in case of chips (crisps). Eye: The colour sense-part of the sense of vision such as brightness, colour, shape and happenings (events). History: Exact sensory of food began in about 1940 in Scandinavian countries with the development of triangle test, a difference test method. At the same time, independent and analogous studies were being carried out in the United States of America. Not until 1950 did European countries start to employ sensory analysis. The first book on sensory analysis was written in 1957 by Tilgner in the polish language and translated into Eastern languages (Czech, Hungarian and Russian). The first published descriptive sensory technique is the Flavor Profile Method (FPM) developed in the 1950s by Arthur D. Little Inc. (Pangborn 1989; Lawless and Heymann 1998; Meilgaard and others 1999). Refinements and variations in FPM occurred in the 1970s with the development of Quantitative Descriptive Analysis (QDA) and the Spectrum™ method of descriptive analysis. Today, descriptive analysis has gained


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wide acceptance as one of the most important tools for studying issues related to flavor, appearance and texture, as well as a way to guide product development efforts. Classification of sensory tests: There are several types of procedures, depending on the specific objective of the evaluation. Also, there are different approaches for classifying the procedures. Many described procedures are currently accepted procedures for such tasks as detecting differences between samples, descriptive analysis of flavor characteristics, quantitative estimates of flavor intensities, rating quality of a product in relation to pre-established standards, identifying preferences, and measuring consumer acceptance. There are four primary types of tests, and these may be classified as Affective, Discrimination, Descriptive and Quality tests. Classification of sensory tests into one of these four categories depends on • • •

The test objective The criteria for respondent selection The specific task required of each respondent

Affective Tests These tests measure the subjective attitudes, such as product acceptance and preference and the task is to indicate preference or acceptance by either selecting, ranking, or scoring samples. The paired-preference and 9-point hedonic scale are popular examples of these types of tests and respondents are usually consumers who are selected on their current or potential use of the product. In laboratory situations, consumer demographics often are substituted in favor of accessible respondents whose preference and acceptance behavior satisfactorily correlate with those of the target consumer population. Laboratory-type acceptance tests can be done with 25 to 50 respondents. In field studies where the target population is used, minimum numbers are increased by 75 to 200 or more. Discrimination Tests Discrimination tests are designed whether samples are detectably different from one another. The most frequently used discrimination test methods are the sequential, paired difference, duo-trio, and triangle tests. The discrimination test is a small panel test, used in a laboratory environment. Using between 12 and 20 qualified subjects, it is possible to make reliable and valid decisions, with each subject providing replicate judgments. Alternatively, one could use 24 to 40 subjects and no replication. Descriptive Tests


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The objective of descriptive tests is to describe sensory properties of products and measure the perceived intensity of those properties. The most popular descriptive methods include classical and modified flavor profile, texture profile and quantitative descriptive analysis (QDA). Typically, 6 to 12 subjects may be used to evaluate a product. Subjects for descriptive tests are screened for their sensory acuity and are then trained to perform the descriptive task. The QDA requires replicate judgments to monitor quantitatively subject performance throughout the course of the test. Results from the descriptive test provide information about product similarities and differences in quantitative terms, thus facilitating development efforts. Quality Tests These provide a score or grade to summarize a product's proximity to a standard. The standard may be a written specification or an actual product selected to embody these specifications. The subject's task differs, as does the quality test itself, depending on the specific industry and product. In most quality tests developed by the dairy industry, subjects also use a single scale consisting of numbers anchored by different word descriptors, or use a procedure that includes a checklist of deficiencies and assignment of a final grade depending on the specific number and kind of deficiencies in the product. A low score on a quality test is intended to indicate deficiencies, as they are defined by experts. Flavor lexicons: A flavor lexicon is a set of word descriptors that describes the flavor of a product or commodity, which is then applied or practiced using descriptive sensory analysis techniques. It provides a source list to describe a category of products, such as commodities or finished products. The descriptive panel produces its own list to describe the product array under study but a lexicon provides a source of possible terms with references and definitions for clarification. For development of a representative flavor lexicon several steps, including appropriate product frame-ofreference collection, language generation and designation of definitions and references are essential before a final descriptor list can be determined. Flavor lexicons, once developed, can be used to record and define product flavor, compare products and determine storage stability, as well as to study correlations of sensory data with consumer liking/acceptability and chemical flavor data. Flavor lexicons should be discriminating and descriptive and the language should be developed from a broad representative sample set that exhibits all the potential variability within the product. Application: Flavor Lexicons have been used for a variety of purposes as: •

They are widely used to describe and discriminate among products within a category.


43

• • • •

•

•

•

They are widely used in industry for comparing and monitoring products and product consistency and for profiling new and competitive products. Used in quality control, with relationships to instrumental or consumer responses. A powerful research tool with numerous applications across many commodities and commercial products. Several different flavor lexicons have been used in cheese to document aroma and flavor development, the effects of fat reduction, and the effects of different starter or adjunct bacteria (Muir and others 1995a; Piggot and Mowat 1991; Roberts and Vickers 1994) Several groups have identified and used descriptive sensory analysis to differentiate fluid milks to determine the effects of fat content, storage, and other processing conditions on milk flavor and aroma perception (Lawless and Claassen 1993; Phillips and others 1995; Phillips and Barbano 1997; Watson and McEwan 1995; Chapman and others 2001; Bom Frost and others 2001). Flavor lexicon for chocolate ice cream has been used to discern the effects of milk fat, cocoa butter, and fat replacers on sensory properties of chocolate ice cream (Prindiville and others 1999, 2000) Descriptive analysis lexicons have also been used for numerous other products including fermented milks, spoiled milk aroma, yogurt etc.

Descriptive Analysis Techniques: Quantitative Descriptive Analysis (QDA) and the SpectrumTM method of descriptive analysis differ markedly from FPM as they are designed to take measurements from individual panelists and then generate a panel average, rather than generation of a group consensus profile as with FPM. However, all 3 techniques involve screening panelists for sensitivity to flavor and aroma and discriminatory ability which is followed by extensive training to generate a group of individuals who can function analogously to an instrument to evaluate flavor of products. Usually fewer panel members are used (minimum 4) in FPM and the panel leader along with other panel member’s work together to generate the language and the method for sample presentation and evaluation. After the panelists are screened for sensory acuity and trained extensively (minimum 60 hr), panelists work as a group to generate a consensus profile of the sensory properties of the product and the intensity of each as well as overall amplitude of the product, as well as a measure of balance and blend is evaluated. The Attributes are evaluated in order of appearance and the scale used for character (descriptor) notes is a 4 point scale (0-not present, 1-slight, 2-moderate, 3-strong) with half point designations in between, for a total of 7 points of discrimination. In contrast to FPM, the panel leader in QDA is a sensory professional, rather than a member of the panel (ideally 8 to 12 prescreened individuals) and does not


44

participate in the discussion to generate the flavor attributes, but facilitates the process to generate the language to describe the product. The order of appearance of the attributes and, thus, orders of evaluation for each descriptor and definitions for each descriptor are generated and additional products, which may further clarify terms, may also be used. Data is collected on scorecards using line scales anchored on each end and the marks are converted to numerical scores by measuring the responses on the scale with a ruler, digitizer, or computerized system. Unlike FPM the data can be analyzed statistically and is traditionally graphically represented using a web plot. A universal intensity scale is usually used in the SpectrumTM method whereas product specific scaling can also be applied. The panel size is similar to QDA and the panelists are screened for cognitive, descriptive and sensory discrimination ability, interest, and availability. By this method, panelists score intensities in the same manner across all attributes. The scales are anchored on either end and can be 15-cm line scales or, more commonly, 0 to 15 numerical scales with tenth subdivisions between, yielding 150 points. The panel leader takes an active role in panel training and along with panel members identifies the sensory language for the product, their order of appearance, and definitions for each term. The data is readily analyzed by statistical techniques and results are normally graphically presented using histograms. Relating Sensory Perception to Consumers Effective consumer tests are used to provide information on consumer liking as descriptive sensory analysis is used to identify and quantify information on the sensory aspects of products. Quantitative consumer liking and/or preference information is obtained from acceptability and preference tests. For this purpose screeners and questionnaires are used to gather demographic data, frequency of usage, and purchase history about a particular product or group of products and these questionnaires are often included with and are recommended with acceptance testing to aid in data interpretation. Identifying drivers of liking or disliking within consumer market segments is also critical for industry to identify which products and product attributes are preferred and by which consumer market segment. In order to relate consumer liking and descriptive sensory properties, several statistical methods are used. Relating Sensory Perception to Chemical Components It is difficult to relate sensory language and chemical volatile compounds because of many reasons: •

•

The relative amount of a compound in a product is not necessarily a measure of its sensory impact, due to different thresholds and the effects of the food matrix. The sensitivity of the extraction technique used must also be taken into consideration.


45

•

There are only a small percentage of the volatile components in a food that are odor-active.

While relating the gas chromatographic data and chemical compounds to sensory impact, 1st step in the solution is gas-chromatography olfactometry (GC/O). The individual compounds in the GC effluent are sniffed and described by a trained panelist and this technique can also be quantitative if the relative intensity of the odorant may also be recorded. Generally three techniques are applied with GC/O: 1. Aroma extract dilution analysis (AEDA) 2. CharmAnalysisTM 3. OSME AEDA and Charm Analysis operate on dilution of samples until an odor is no longer detected and the highest dilution at which the odor is detected can be converted to a flavor dilution value (FD value used with AEDA) or a Charm value. These techniques are time consuming because of large number of sample dilutions by at least 2 panelists. Moreover these techniques also assume that the response to a stimulus as well as response to all compounds is linear. On the other hand, Osme, does not involve dilutions, but instead requires panelists (3 or more) to evaluate the time-intensity of aromas and aroma character. Recently a new olfactometry technique i.e. nasal impact frequency (NIF) has also been developed which is based on frequency of detection of a compound in the GC effluent by sensory panelists. This technique can be applied with time intensity to yield surface of nasal impact frequency (SNIF) data. Both Osme and NIF/SNIF require fewer GC runs than AEDA and CharmAnalysis, because only undiluted flavor extract is evaluated by the sensory panelist but a larger number of panelists (3 or more, compared to 2 for AEDA and CharmAnalysis) is recommended for these techniques. All of these techniques are useful for determining odor activity of volatile compounds and the information obtained is based on individual components and does not include matrix effects or the time release factor involved when a sample is chewed in the mouth. Conclusions: The importance of sensory analysis has grown and requires more scientific attention. Flavor lexicons are an important tool for accurately documenting the description of food flavor. More research is expected and needed to demonstrate the effectiveness of the methodology and its practical application. References: Bom Frost M, Dijksterhuis GB, Martens, M. 2001. Sensory perception of fat in milk. Food Qual Pref 12:327-36.


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Chapman KW, Lawless HT, Boor KJ. 2001. Quantitative descriptive analysis and principal component analysis for sensory characterization of ultrapasteurized milk. J Dairy Sci 84:12-20. Lawless HT, Claassen MR. 1993. Validity of descriptive and defect-oriented terminology systems for sensory analysis of fluid milk. J Food Sci 58:108-12,119. Meilgaard MM, Civille GV, Carr, T. 1999. Sensory Evaluation Techniques. 3rd Ed. New York, NY: CRC Press. 387 p. Muir DD, Hunter, EA, Watson M. 1995a. Aroma of cheese. 1. Sensory characterization. Milch 50:499-503. Lawless HT, Heymann H. 1998. Qualitative consumer research methods. In: Sensory Evaluation of Food. New York NY: Chapman and Hall. p 519-47. Pangborn RM. 1989. The evolution of sensory science and its interaction with IFT. Food Technol 43:248-56, 307. Phillips LG, Barbano DM. 1997. The influence of fat substitutes based on protein and titanium dioxide on the sensory properties of low fat milks. J Dairy Sci 80:2726-31. Piggot JR, Mowat RG. 1991. Sensory aspects of maturation of Cheddar cheese by descriptive analysis. J Sens Stud 6:49-62. Prindiville EA, Marshall RT, Heymann H. 1999. Effect of milk fat on the sensory properties of chocolate ice cream. J Dairy Sci 82:1425-32. Prindiville EA, Marshall RT, Heymann H. 2000. Effect of milk fat, cocoa butter, and whey protein fat replacers on the sensory properties of low fat and nonfat chocolate ice cream. J Dairy Sci 83:2216-23. Roberts AK, Vickers ZM. 1994. Cheddar cheese aging: changes in sensory attributes and consumer acceptance. J Food Sci 59:328-34. Watson MP, McEwan JA. 1995. Sensory changes in liquid milk during storage and the effect on consumer acceptance. J Soc Dairy Technol 48:1-8.


47

SESNORY ATTRIBUTES OF CONCENTRATED MILK AND THEIR EVALUATION

Dr. R.R.B. Singh Senior Scientist Dairy Technology Division NDRI, Karnal 1.

Introduction

Critically quality assessment of all classes of concentrated milk challenges both the dairy products judge and the manufacturer of these products. A thorough understanding of the sensory attributes of concentrated milk and their routine examination is imperative, not only to assure improvement of the product, but also for ensuring that the product reaches the consumer in good condition. 2.

Evaporated Milk

When judging or grading evaporated milk, the judge must keep in mind the desirable qualities and standards for the product. It must be noted that, in addition to meeting the legal chemical requirements for the product high quality evaporated milk must be white to creamy in colour, have a relatively viscous body, uniformly smooth in texture and possess a mild, pleasant flavour (Bodyfelt et al., 1988). A complete examination of evaporated milk includes test and observations on colour, container, fat separation, fill of container, film formation (protein break), flavour, gelation, sedimentation, serum separation, viscosity and whipping ability. Some of the subjective tests, based on organoleptic examination, make use of the hedonic scale or variations of it. For example, the flavour of evaporated milk may be given a hedonic rating on a 9-point scale discussesd earlier under “Sensory tests”. A narrow band hedonic scale say, a 5-point one , may be used in rating organoleptic quality factors other than flavour. 2.1

Procedure for examination

A routine in examining cans of evaporated milk facilitates judging of the samples. The following steps have been found to be of material aid in going over a lot of samples: Precaution: Avoid undue agitation when transporting the cans to the laboratory. a) Examine the cans for appearance, notice the upper end of the can for polish; observe the neatness of the label.


48

b) Open the can in such a way that both the can and contents can be examined. c) Notice the colour of the milk which should be uniformly white to cream colour. Intensity of darkening may be noted for its degree e.g. non, slight, distinct and pronounced. d) Study the body and texture. Smooth, relatively viscous evaporated milk pours like a thin cream without marked splashing. Allow the can to drain well. Look for any deposit which may be present in the bottom of the can. Should the milk lack uniformity try to determine whether the chief factor is fat, protein, salts or foreign material. In case the fat is responsible, the defect will appear at the top of the can as a cream layer or as buttery particles. Defect due to protein will appear as various size curds distributed throughout or as different intensities of gelation. e) Observe the condition of the container looking for splangling, blackening of the seam and rusting of the container. Splanging appears as clean, bright, dark, overlapping blotches on the surface as though the tin were attacked by acid. f) Determine the colour reaction in coffee. It should be a rich, golden brown colour. Off flavour may be associated with rust formation in the container. g) Note the miscibility with coffee. Feathering in hot coffee appears as finely divided, serrated curds shortly after the evaporated milk has been added slowly to the hot coffee. 2.2

Defects in evaporated milk

2.2.1

Flavour

The flavour defects, which may occur in evaporated milk are usually unlike those commonly occurring in fresh beverage milk. Probably the most common flavour defect in evaporated milk is that which seems to be associated with progressive age darkening or browning of the product. Terms such as slightly acid, stale coffee, old, sour and strong suggest the nature of the defect. The caramel flavour connotes a pleasant, appetizing taste sensation that is definitely lacking in the defect associated with age-darkening of evaporated milk. This flavour defect is easily detected. The off-flavour is accompanied by only a slight odour suggesting staleness. The underlying taste reaction of the age-darkened evaporated milk is acid. 2.2.2

Body and Texture

Fresh evaporated milk is remarkably free of body and texture defects. However, when evaporated milk is held for a long period of time or under adverse conditions, the following body and texture defects may be encountered: 2.2.2.1 Fat separation: This defect appears as a layer (up to 1more thick) of fat the top of the can. Among the causes of this defect are inadequate from isolation,


49

high storage temperature, long storage period and impetrated handling while in store. 2.2.2.2 Curdy: Curdy evaporated milk may be noted by the presence of many coagulated particles inter spread throughout the milk or by a continuous mass of coagulum. It is chiefly associated with the protein rather than the fat. It is a serious economic defect. This condition is due mainly to abnormally low heat coagulation point of the end product and could not withstand the sterilization process. 2.2.2.3 Feathering: The feathering of evaporated milk in hot coffee cannot be foretold by macroscopic examination but by actually testing the milk in hot coffee. It has been postulated that the formation of the curd when evaporated milk is added to coffee is due entirely to an excess of viscosity. 2.2.2.4 Gassy: Gassy evaporated milk is rather uncommon. The defect is manifest by bulged cans and sometimes by a hissing sound of escaping air when the can is punctured. 2.2.2.5 Grainy: A grainy evaporated milk is the one, which lacks smoothness and uniformity, throughout. Such milk seems coarse. It is often associated with an excessively heavy, viscous body. The judge must bear in mind that grainy evaporated milk does not actually contain “grains” of sediment settled in the container. Neither does such milk contain curds or lumps of butter. 2.2.2.6 Low viscosity: A low viscosity evaporated milk may be noted by its milk like consistency. This defect is discriminated against as it connotes inadequate condensation. 2.2.2.7 Sediment: The sediment resulting from settling of leukocytes, disintegrated cells, denatured protein and foreign material of more or less of a colloidal nature is usually darker in colour than the evaporated milk. Since this sediment is readily miscible it may be seen only when a can, undisturbed for sometime, is emptied slowly. The other type of sediment noted in evaporated milk is the result of the crystallization of some of the calcium and magnesium salts as Ca3 (PO4)2 and Mg3(PO4)2. This gritty sediment formation accompanies ageing of the evaporated milk. They are found in the bottom of the container where they may be noted especially when the contents are emptied. 2.2.3

Colour

In judging evaporated milk two possible colour defects may be encountered, viz. too light in colour and too dark in colour. Too light colour is not a serious defect although it is definitely not desired. The brown discoloration in evaporated milk associated with high sterilization temperature, high storage temperature and age is a serious defect in evaporated milk.


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3.

Sweetened Condensed Milk Since sweetened condensed milk contains a sufficiently high percentage of sugar for its preservation, the flavour is pronouncedly sweet. Beyond this intense sweeteness, the flavour should be clean and pleasant with a slight trace of mild caramel as an aftertaste.

3.1

Procedure for examination A definite routine examination enables the judge to make the best use of the available time with the assurance that the examination is complete when finished (Seehafer, 1967). a) Appearance of the container should be as bright as new tin as the can has not been subjected to the high heat treatment of sterilization. b) The surface of the product should have the same intensity of colour as the under layer and should be uniform in consistency with no indication of lumps, free fat or skin formation. c) Colour of the product should be uniform throughout. Observe if the milk has a greenish white creamy or a brownish colour. d) Viscosity desired is one which is obviously not “thin” but resembling to a marked degree that of medium – heavy molasses. In grading sweetened condensed milk, the judge must bear in mind that a desirable sweetened condensed milk pours like molasses and, when poured, seeks its own level leaving no trace of the folds on the surface. e) Flavour should be observed both for the textural and taste sensations. Register the relative smoothness of the product as a whole and fineness of the grain by pressing the sample against the palate with the tongue.

3.2

Defects of sweetened condensed milk

3.2.1

Flavour

3.2.1.1 Metallic: The metallic flavour in sweetened condensed milk is chemical rather than bacterial in nature and is usually traceable to copper contamination. 3.2.1.2 Rancid: It occurs rather infrequently and resembles butyric acid. Rancid flavour increases in intensity with age. 3.2.1.3 Strong: It is a flavour defect, which is suggestive of caramelized sugar and is usually accompanied by brown tint to the natural colour.

3.2.2

Body and texture


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Condensed milk, having a high percentage of sugar has a relatively heavy body somewhat like normal molasses. Also, it usually has a smooth, uniform texture. However, the product may have certain body and texture defects such as buttons or lumpiness, fat separation, gassiness, sandiness, sediment, thickening etc (Gupta and Patel, 1978). 3.2.2.1 Buttons/lumpy: It is a body defect which is characterized by the presence of round and firm lumps, with stale odour, at the surface of the product. Buttons result from enzymic action following mould growth. 3.2.2.2 Sandy, rough, grainy, granular: These terms are used to describe sweetened condensed milk, which contains oversized lactose crystals. The solid particles are of such size that the product lacks smoothness and grittiness is noticeable, as the sample is being tasted. 3.2.2.3 Settled: It is used to describe the condensed milk in which a definite settling of sugar crystals has occurred. 3.2.2.4 Thickened: This defect is manifest by a gel formation, which gives the product the appearance of a solid rather than a liquid. The defect varies markedly in its intensity from a slightly jelly to a firm custard consistency.

References BIS. (1981) Method for Sensory Evaluation of Sweetened Condensed Milk. IS: 10029-1981, Bureau of Indian Standards, New Delhi. Bodyfelt, M.S.; Tobias, J. and Trout, G.M. (1988) The Sensory Evaluation of Dairy Products, Publ. pp. 416-472. Gupta, S. K. and Patel, A.A. (1978). Some aspects of judging condensed milk. Indian Dairyman, 30: 713-715. Seehafer, M.E. (1967) The Development and Manufacture of Sterilized Milk Concentrate. FAO Agricultural Studies Bulletin. No. 72, pp. 1-52.


52

Table A. Score card for organoleptic evaluation of UHT milk. Name of Judge_____________ Date ___________________ Attributes

Perfect Score

Criticism 1

Flavour

45

Score Asstringent/chalky Bitter Cabbage Coconut Cooked Flat Oxidised/cardboardy Paper like Phenolic Rancid Sour Stale

Consistency

20

Score Thin Heavy/viscous Gel/ Custard like

Colour & Appearance

15

Score

2

Sample Number 3 4 5

6

Dull Browning Fat separation Sedimentation

15

Score

Package

5

Score Distorted/ Bulged Dented Leaky Soiled

Total Score

100

General guide for grading UHT milk or the basis of total score: Excellent Good Fair Poor Bad

95 and above 90-94 85-89 75-84 Below 74


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Table B. Suggested score for evaluation of different intensities of defects. Defect

Slight

Definite

Pronounced

Flavour Astringent/chalky Bitter Cabbage Coconut Cooked Flat Oxidized/ Cardboardy Paper-like Phenolic Rancid Sour Stale

37 32 37 32 42 38 32 34 32 32 28 33

32 27 34 27 40 33 27 29 27 27 23 28

27 22 31 22 38 28 22 24 22 22 18 23

Consistency Gel (Custard like) Heavy/Viscous Thin

12 18 18

8 16 16

4 13 15

11 13.5 11

10 13 10

8 12.5 8

Sedimentation

12

10

7

Package Dented Distorted or Bulged Leaky Soiled

4 4.4 3.0 3.5

3.6 4.0 2.0 3.1

3.2 3.6 1.0 2.7

Colour and Appearance Browning Dull Fat Separation

Table C. General guide for grading UHT milk on the basis of various sensory attributes. Characteristics

Flavour

Grade

Range of Score

Specific description of criticism

Excellent

41-45

Slightly cooked.

Good

36-40

Slightly astringent / chalky, cabbagy, flat; definite to pronounced cooked.


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Consistency

Colour and Appearance

Sedimentation

Package

Fair

31-35

Slightly bitter, coconut, oxidized, paper like, phenolic, rancid, stale; definite to pronounced cabbagy flat.

Poor

26-30

Slightly sour; definite bitter, coconut, oxidized, paper like, phenolic, rancid, stale; pronounced chalky. Contd..

Bad

Below 25

Excellent

19-20

No criticism.

Good

17-18

Slightly thin, viscous/heavy.

Fair

15-16

Definite to pronounced thin, definite heavy.

Poor

13-14

Pronounced viscous.

Bad

Below 12

Gel, Custard like.

Excellent

13.6-15.0

No criticism

Good

12.1-13.5

Dull colour.

Fair

10.6-12.0

Slightly brown, slightly fat-separation.

Poor

9.1-10.5

Definite brown, fat – separation.

Bad

Below 9

Pronounced brown, fat – separation.

Excellent

13.6 – 15.0

Good

12.1-13.5

No visible sediments but chalky perception in mouth suggesting presence of sediments in soluble particles form.

Excellent

4.6 - 5.0

No criticism.

Good

4.1 – 4.5

Slightly distorted or bulged.

Fair

3.6 –4.0

Dented package; definitely distorted or bulged.

Poor

3.1 –3.5

Soiled package.

Bad

Below 3

Leaky package.

Definite sour; pronounced bitter, coconut, oxidized, paper like, phenolic, rancid, stale.

No criticism.


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SENSORY ATTRIBUTES OF FERMENTED MILK PRODUCTS

Dr. Latha Sabikhi Senior Scientist Dairy Technology Division NDRI, Karnal 1. Introduction Cultured milk products, which include dahi, yoghurt, lassi, buttermilk, shrikhand, sour cream and kefir, play an important role in the dairy industry. Their low pH and extended shelf life make cultured milk products particularly relevant to commercial production in tropical countries. While sensory attributes are very important determinants of the acceptability of cultured milk products, their sensory evaluation has not progressed to the same extent as the art and science of sensory discrimination for milk and many other manufactured milk products. Generally, sensory evaluation of commercial fermented milk and cream products has frequently involved more of a comparison of the products of current manufacture with those made previously. This procedure, however may tend to result in a progressively lower quality product. 2. Common Attributes of Cultured Milk Products 2.1 Flavour Cultured milk products should impart a pleasing bouquet flavour, which results from the overall blend of a delicate, diacetyl odour and a distinctly clean, acid taste. Once the aroma and taste characteristics of good-cultured products are fixed in the mind of the evaluator they are not easily forgotten. Sometime there is possibility of occurrence of one or more of several off flavours, such as bitter, cheesey, lack of desired aroma, lack or flavour and high acid. 2.2 Body and Texture Before being shaken the body of a good, properly cultured product should appear firm or solid and generally be uniform in appearance. It should only show a few beads of whey exuded from the surface. The mix sample should appear smooth, somewhat resembling rich cream, no curd particles or lumps should appear when in is spread in a thin layer in a glass surface or diluted with water. Some of the more common body defects of cultured milk products are described in the following paragraphs. Sensory and Related Techniques for Evaluation of Dairy Foods

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2.2.1 Curdy: A curdy body tends to lack uniformity, smoothness or homogeneity. The curd particles may be sufficiently large to be readily observed upon pouring or so small in size that close examination is necessary to see the feathens curds.

2.2.2 Lumpy: A “lumpy” body is often an aggravated case of curdy consistency; the particle size is larger in the lumpy defect.

2.2.3 Gassy: A “gassy” product is denoted by excessive gas bubbles (CO), or by streaks in the coagulum due to rise of gas bubbles to the surface. If accompanied by whey separation, a gassy sample will whey off at the bottom or at the centre of the container.

2.2.4 Ropy: A ropy product tends to stretch or string – out when poured. Sometimes the defect is so pronounced that the product strings out like a thin syrup or mucous substance.

2.2.5 Wheying-off: This defect is manifest by a shrunken curd or coagulum and the presence of liberated or “free whey” in areas around the side and on the surface of the container. 3. Yoghurt Yoghurt is a quickly curdled milk based product with little or no alcohol content. It results from the associative growth of Lactobacillus bulgaricus and Streptococcus thermophiolus in warm milk (29-45oC). Typical yoghurt is characterized by a smooth, viscous gel, with a taste of sharp acid and a green or green apple flavour some yoghurt exhibit a heavy consistency that closely resembles custard or milk pudding by contrast, other yoghurt are purposely soft –bodied and essentially drinkable. Different type of yoghurt sold in the USA and their characteristics are given in Table 1. 3.1 Desirable attributes of yoghurt Yoghurt should be smooth, viscous gel, with a characteristic taste of sharp acid and a green or green apple flavour. The typical acetaldehyde flavour of plain yoghurt is achieved through a symbiotic bacterial relationship is flenced by such factors as (1) temperature of incubation, (2) amount of inoculum (3) period of incubation, (4) source of culture, (5) heat treatment of yoghurt base and (6) pH of finished products. The flavour of plain yoghurt is somewhat unique and unlike that


57

encountered in any other type of fermented milk. The flavour components of plain yoghurt flavour include acetaldehyde acetic acid, diacetyl and several volatile falty acids. Table 1 Characteristics of the various styles of flavoured yoghurts in U.S.A. Characteristics

Yoghurt style (Type) 1

Swiss –Style (French –

Precultured yogurt base and fruit or berry flavoring

prestirred, or

(15-25%) blended prior to packaging

Preblended 2

Sundae-style

Flavouring (15-25%) added to the container, yogurt

(Fruit-on-bottom)

base added to top of flavouring.

a. Eastern-type

No colouring agent, flavouring, or sweetener added to yogurt base (milk base is white).

b. Western-type

Colouring agent, flavour extract, or concentrate and/or sweetener added to yogurt base.

c. Fruit-on-top

Yogurt cups filled in a manner so that flavouring material is on top portion of container.

3

Extract flavored

Flavour extracts and or concentrates are sole source

(or concentrates)

of flavour plus sweetener(s) (i.e., coffee, chocolate, lemon etc.)

4

Frozen Product Form a. b. c. d.

Soft serve Hard frozen Novelties Yogurt pies

Served as cones, dish or sundaes. Pint and quart size On-a-stick, coated bars, “push-ups”. In “pie” crusts.

5

Miscellaneous Types

A variant of the sundae-style Western type: A firm, flavored yogurt with additional flavoring cascading over its exterior when emptied up-side down.


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3.2 Defects in yoghurt 3.2.1 Plain yoghurt Colour and appearance consideration for plain yoghurt are rather simple and straightforward, compared to the complexities of flavoured yoghurt. Generally, the appearance of plain yoghurt should convey a smooth, homogenous, moderately firm gel or custard-like body and texture and a uniform off-white color. The more common color an appearance defects of plain yoghurt are reviewed here. 3.2.1.1 Free whey: Wheyed-off (Syneresis) This defect is manifest by a shrunken curd’ or coagulum and the presence of liberated or “free whey” in areas around the side and on the surface of the container. 3.2.1.2 Gel-like: This condition may be considered as both an appearance and a body and texture defect. The term “gel-like” is used to describe the appearance of excessive product firmness, or a severe gelatin (liver like) consistency. 3.2.1.3 Shrunken: Occasionally in yoghurt, the gel or coagulum tends to shrink in size within the container (or pull away from the carton side wall); this leaves the impression of reduced or “shrunken” contents. Quite often, free whey will fill the void that results from this “shrinking” of the coagulum. 3.2.1.4 Surface Growth: Probably the most serious defect of yoghurt appearance. This defect consists of visible colonies of yeast and/or mold growth on the top surface of the yoghurt. 3.2.2 Body and texture defects 3.2.2.1 Grainy: In the instance of “graininess,” the product lacks the desired smoothness and uniformity of appearance. Small particles of a grit or grain size may actually be visible; graininess is quite often detectable by mouthfeel. 3.2.2.2 Ropy: A ropy product tends to stretch or “string-out” when poured. Sometimes the defect is so pronounced that the product “strings-out” like a thin syrup or mucous substance. 3.2.2.3 Too Firm: When the body of plain yoghurt is considered “too firm”, it conveys the impression of being too rigid or resistant to mastication when placed in the mouth. Also, a too firm body is often apparent by visually examining a side profile of a spoonful of product. Firm or rigid edges can be noted, rather than a more preferred “soft rounding” impression of a spoonful of product. 3.2.2.4 Weak: A weak body defect is the exact opposite of too firm; the product consistency conveys the distinct impression that it would probably be easier to consume the product as a beverage than to “spoon” it. Viewed from side profile, the product may appear practically level in the spoon, or it may spill over the lip of the spoon. For drinkable style yoghurt, a weak body is a prerequisite.


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3.3 Procedure for yoghurt evaluation A scorecard for swiss-style flavoured yoghurt (fig.1) developed and adopted by the Committee on Evaluation of Dairy products of the American Dairy Science Association carries maximum scores for different attributes (Table 2) and can be used as per the guidelines given in Table 3. This scorecard was cooperatively designed through the suggestions and efforts of ingredient suppliers and commercial yoghurt manufacturers. Table 2. Maximum scores for the sensory attributes of yoghurt Attributes

Maximum Score

Normal range

Flavour

10

1-10

Body and texture

5

1-5

Appearance

5

1-5

Product acidity

2

-

Container and closure

3

-

Table 3: Scoring guide for the sensory defects of Swiss-style yoghurt Intensity of Defect

Criticisms Slight

Definite

Pronounced

Acetaldehyde (green)

9

7

5

Acid (too high)

9

7

5

Acid (too low)

9

8

6

Bitter

9

7

5

Cooked

9

8

6

Foreign

5

3

0

Lacks fine flavour

9

8

7

Flavour


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Lacks flavouring

9

8

7

Lack freshness

8

7

6

Lacks sweetness

9

8

7

Old ingredient

7

5

3

Oxidized/metallic

6

4

1

Rancid

4

2

0

Too high flavouring

9

8

7

Too sweet

9

8

7

Unclean

6

4

1

Unnatural flavouring

8

6

4

Gel-like

4

3

2

Grainy/gritty

4

3

2

Ropy

3

2

1

Too firm

4

3

2

Weak/too thin

4

3

2

Atypical colour

4

3

2

Colour leaching

4

3

2

Excess fruit

4

3

2

Lacks fruit

4

3

2

Lumpy

4

3

2

Shrunken

4

3

2

Surface growth

2

1

0

Wheyed-off (syneresis)

4

3

2

Body and texture

Appearance


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4. Lassi Lassi, popular Indian soft drink is a product resulting from the growth of a selected culture usually lactic streptococci in heat treated whole or partially skimmed milk. At the desired ripeness 0.75-0.85% lactic acid, the coagulum is broken, admixed with sugar (or sugar syrup), and flavour and packaged in glass bottles or polyethylene bags. It is stored under refrigerated conditions and invariably served cold. 4.1 Desirable characteristics of lassi The color of lassi should be pleasing, attractive and uniform. Normally, it varies from light yellow to whitish. In general, the good, clean, pleasant diacetyl flavour of a culture is desired in lassi. The natural flavour may be enhanced or enriched by the presence of milk fat. The demands of trade vary as to the body of lassi. Some consumers prefer a heavy viscous body while others like a rather thin body. Consequently, no uniform standard can be fixed with regard to the body of lassi. However, a medium-bodied lassi pouring similar to thin gravy seems to be most appropriate. The texture should be homogenous showing no signs of wheying off or grains or curd particles. 4.2 Score card for lassi A scorecard based on 100-point scale is shown in Fig 1 and the guidelines given in Table 3. Attribute

Perfect Score

Sample Score 1 2 3 4 5

Flavour

45

-

Body & texture

30

-

Acidity

10

-

Colour & appearance

10

-

Container & closure

5

-

100

-

Total


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Table 3. Suggested deductions sensory attributes of lassi

Sensory Flavour (45)

from

Defect

maximum

score

for

different

Intensity of defect Slight

High acid/green cheesy,

Definite Pronounced

7

9

11

metallic

10

13

16

Body and Texture

Curdy grainy, thin/thick

1

3

5

(30)

body Ropy, 3

6

9

1

3

5

1

3

5

1

2

3

bitter,

wheying off Acidity (10)

High acidity, Low acidity

Color &

Uneven/unnatural colour

Appearance (10) Container and

Dirty/improperly

closure (5)

covered

5. Shrikhand Shrikhand is an acid coagulated and sweetened milk product, which is a popular delicacy in states of Gujarat, Maharashtra and partly Karnataka. This indigenous dairy product is prepared by lactic coagulation of milk and expulsion of whey from the curd followed by blending of sugar, flavour and spiced. The product has about 5% fat, 42% sugar and 60% TS. The shelf life of the product is about 40 days at 8+1oC. A 100-point score card similar to the one shown in figure 2 carries a maximum score of 55, 30, 10 and 5 for flavour, body and texture, appearance and color respectively. The sensory guide is given in Table 3 and 4. 6. References Conolly, E.J., White, C.H. Custer, E.W. and veda muthu, E.R. (1984) Cultured Dairy Food Quantity Improvement Manual, American Cultured Dairy Products Institute Washington D.C.


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Duthie, A.H; Nilson, K.M. Atherton, H.V. and Garrett, L.D. (1977) Proposed score card for yoghurt. Cultured Dairy Product J., 12 (3) 100 Kemp, N. (1984) Kefir, the champagne of cultured dairy products. Cultured Dairy Product. J. 19(3): 29 Ryan, J. M., White, C.H. Goush, R.H. and Burns, A.C. (1984) Methodology for evaluation of yoghurt. J.Dairy Sci, 67: 1369 Dharam Pal and Gupta, S. K. (1985) Sensory evaluation of Indian Milk Products. Indian Dairyman 37: 465 Patel, R.S. (1982) Process Alterations in shrikhand technology, Ph.D. Thesis, Kurukshetra University, Kurukshetra


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APPLICATION OF E-TONGUE IN MONITORING SENSORY QUALITY OF FOODS Dr. S.K. Kanawjia, Sanjeev Kumar*, Hitesh Gahane** and Vikash Gupta Principal Scientist Cheese and Fermented Foods Lab, D.T. Division, NDRI, Karnal * PhD Scholar, ** M.Tech (DT) Scholar, *** Research Associate E-mail: [email protected] Introduction New product development requires the integration of sensory attributes including product taste, texture, and appearance with consumer attitudes and health biases. Both sensory and attitudinal variables determine food preferences, product purchase and food consumption. This paper describes application of the e-tongue to eliminate panelist bias for taste evaluation of food products. The evaluation of dairy and food products for their organoleptic properties is one of the essential requirements for development of newer items as well as its perfection at the stage of production or marketing. Taste is the most important sensory attribute of any food product, which determines its acceptability. The senses of taste have always been used in monitoring and judging the quality of foods. The application of human taster to distinguish different tastes is as older as the human civilization. Unfortunately, there are several problems associated with human taster which include sensory fatigue, varied perception of similar taste to different people, health risk as associated with tasting of certain chemicals and its dependability on human mood and adaptation. In the era of sensor technology, evolution of E-Tongue has initiated renaissance in sensory assessment of foods. E -Tongue mimics the biological tongue, which is actually a group of sensor chips capable of remitting real time data to control the quality of a liquid process. When a liquid flows over this "tongue," its exact chemical makeup can be ascertained and controlled by computer. This innovation is expected to save several lacks of rupees in industrial quality control. The tongue can "taste" liquids to detect impurities or anomalies, offering possibilities for improving water purification, blood and urine tests, even the fermentation of champagne. Using chemical sensors, University of Texas at Austin, researchers have designed an E-tongue that can taste like its natural counterpart. It has the potential someday to distinguish between a dazzling array of subtle flavour using a combination of the four elements of taste viz. sweet, sour, salt and bitter. In some ways it has outdone Mother Nature: it has the capacity to analyze


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the chemical composition of a substance as well. The device, which has the potential to incorporate hundreds of chemical micro sensors on a silicon wafer, has a multitude of potential uses. The food and beverage industry wants to develop it for rapid testing of new food and drink products for comparison with a computer library of tastes proven popular with consumers. E-Tongue is the most advanced device of its type worldwide and has no analogues. The know-how of the system is not disclosed in scientific papers, the patent aspects are under study. Historical Background E-Nose only measures volatile components only, which constitutes a sample’s odour. Human sensory perception encompasses more than just odour and aroma and includes taste, colour, texture, mouth-feel, and even sound. As E-Nose is used more routinely, instrument suppliers have continued to provide improved solutions The tongue research, reported in the Journal of the American Chemical Society, began in 1996 when electrical and computer engineering professor Dean Neikirk and chemists John McDevitt and Eric Anslyn began casual discussion of the idea. Neikirk and McDevitt designed a nose to sniff out iodine, but soon realized that many chemicals don't evaporate. The new collaboration incorporated the work of Anslyn, a chemist and tongue researcher at the University of Texas at Austin, who used polymer micro beads to synthesize DNA and its proteins. The team attached four well-known chemical sensors to Anslyn's minute beads and placed the beads in Neikirk's micro-machined wells on a silicon wafer. Like a human tongue, the wells mimicked the tongue's many cavities that hold chemical receptors known as taste buds. Each bead, like a tongue's receptor, had a sensor that responded to a specific chemical by changing colour. One turned yellow in response to high acidity, purple under basic conditions. Then the researchers read the sensor's results through an attached camera-on-a-chip connected to a computer. The sensors responded to different combinations of the four artificial taste elements with unique combinations of red, green and blue, enabling the device to analyze for several different chemical components simultaneously. Alpha M.O.S., Toulouse, France, has now launched an E-Tongue for the analysis of taste and non-volatile chemicals that are typically found in liquids.

Development of E-Tongue One of the overall goals of NASA's Space Life Sciences Division of Advanced Human Technology Program (AHST) research project is to understand the principles, concepts, and science which will enable the development of an integrated, rugged, reliable, low mass/power, electro analytical device which can identify and quantitatively determine a variety of water quality parameters including, inorganics, organics, gases along with physical properties like pH, oxidation reduction potential, and conductivity. The mission of its Advanced Environmental Monitoring and Control Program (AEMC) is to "provide spacecraft with advanced, microminiaturized


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networks of integrated sensors" to monitor and control the environment. One of the main components of the AEMC program is the development of advanced technologies for monitoring the chemical and physical status of life support systems i.e. the water supply. To accomplish these goals a group of scientists in collaboration with the NASA's Jet Propulsion Laboratory and Thermo Orion Research, undertook the research necessary to lead to an electrochemically-based integrated array of chemical sensors based on several novel transduction and fabrication concepts. Even though this type of sensor array might be thought of as an "Electronic Tongue", it is exceedingly more capable. Working in conjunction with a neural network, it will provide both qualitative and quantitative information for a much broader range of components, such as cations, anions, inorganic and organic than a human tongue ever could. The micro fabrication, integration, and multiplexing of such a large number of sensors on a single substrate has not been previously attempted and presents a formidable scientific and technical challenge. Their work has lead to the discovery of a unique electro-immobilization technique, which imparts special selectivity properties to each sensor. Unlike previous devices though, this electrochemicallybased sensor will provide both identification and reliable quantitative data. The technology resulting from this research project has been proposed to be used in a taste of future: the E-Tongue. E-Nose developed by collaboration between the Jet Propulsion Laboratory and the California Institute of Technology analyzes gases in a similar way and was the precursor to E-tongue research at University of Texas. From the silicon tongue, the team hoped to create a process to make artificial tongues more cheaply and quickly, placing them on a roll of tape, for example, to be used once and thrown away.

E-Tongue Capability The researchers designed E-Tongue to be structurally similar to the human tongue, which has four different kinds of receptors that respond to distinct tastes. The human tongue creates a pattern in the brain to store and recall the taste of a particular food. E-Tongue is an analytical instrument comprising an array of chemical sensors with partial specificity (cross-sensitivity) to different components in solution, and an appropriate method of pattern recognition and/or multivariate calibration for data processing. It is a new generation analytical instrument based on an array of nonselective chemical sensors (electrodes) and pattern recognition methods. Chemical sensors incorporated into the array exhibit high cross-sensitivity to different components of analyzed liquids inorganic and organic, ionic and non-ionic. Utilization of the sensors with high cross-sensitivity in conjunction with modern data processing methods permits to carry out a multi-component quantitative analysis of liquids (determination of composition and components), and also recognition (identification, classification, distinguishing) of complex liquids.


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The instrument is a multisensor system for liquid media analysis only. It consists of a multisensor system (sensor unit) incorporating 15 to 40 different sensors, an electronic interface device for measuring and conversion of the sensor signals and a PC for data acquisition and processing. Not only is E-Tongue a technological breakthrough; it is also a myth-buster about the character of academic research in the era of electronics. E-Tongue may be called a micro machined sensor array that has been developed for the rapid characterization of multi-component mixtures in aqueous media. The sensor functions in a manner analogous to that of the mammalian tongue. Likewise, the sensor creates specific patterns for different mixtures of analytes. These "taste buds" are deposited into an array of micro machine-etched wells localized on silicon wafers. The hybrid micro machined structure has been interfaced directly to a charged-coupled-device (CCD), which is used for the simultaneous acquisition of the colorimetric data from the individually addressable "taste bud" elements. With the miniature sensor array, acquisition of data streams composed of red, green, and blue (RGB) colour patterns distinctive for the analytes in the solution are rapidly acquired. E-Tongue contains tiny beads analogous to taste buds. Each "bud" is designed to latch onto specific flavour molecules and change colours when it finds one, be it sweet, sour, bitter or salty. The buds are housed in pits on the surface of the tongue itself, which is made of silicone. Each one of these pits looks like a little pyramid, and it's just the right size that we can take one of these taste buds and nestle it down inside. A little silicon chip that has micro beads arrayed on it, in a similar fashion to the taste buds on your tongue has been made at the university of Texas. Each of the beads responds to different analytes like the tongue responds to sweet, sour, salty, and bitter. There is a potential to make taste buds for almost any analytes. To build E-Tongue, the scientists’ positioned 10 to 100 polymer micro beads on silicon chip about one centimeter square. The beads are arranged in tiny pits to represent taste buds and marked each pit with dye to create a red, green, and blue (RGB) colour bar. The colours change when the chemicals are introduced to E-Tongue. A camera on a chip connected to a computer then examines the colourrs and performs a simple RGB analysis that in turn determines what tastes are present. Yellow, for example, would be a response to high acidity, or a sour taste. The E-Tongue now uses simple markers to detect different types of taste: calcium and metal ions for salty, pH levels for sour, and sugars for sweet. E-Tongue features an auto-samples and integrated software (Giese, 2001). It is designed to replicate human taster and consists of an array of chemical sensors, each with partial specificity to a wide range of non-volatile taste molecules, coupled with a suitable pattern recognition system. For instance, The Alpha M.O.S. E-Tongue, called the Astree, is composed of a 16-position auto sampler, an array of liquid sensors, and an advanced chemo metric software package (Alpha M.O.S, 2001 a, b, c). The instrument also has an option of sample temperature control to ensure analytical producibility of measurements.


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Features of E-Tongue One of the unique features of the system is the possibility to correlate the output of E-Tongue with human perception of taste, odor and flavour, e.g. with food evaluations made by a trained taster. A typical sensitivity limit of most such sensors for the majority of components is about several micrograms per liter. Of primary importance are stability of sensor behaviour and enhanced cross-sensitivity, which is understood as reproducible response of a sensor to as many species as possible. If properly configured and trained (calibrated), E-Tongue is capable of recognizing the quantitative and qualitative composition of multi-component solutions of different natures, e.g. beverages and foodstuffs. E-Tongue is not affected by CO2 concentration in the product .It responses to a number of organic and inorganic nonvolatile compounds in the ppm level in liquid environment .The response can be highly reproducible. In any E-Tongue application, results will be as good as the samples used in the calibration and teaching the sets.

Principle of E-Tongue Humans have long been thought to detect four basic taste types viz. sweet, salty, sour and bitter. Very recently, a fifth candidate basic taste was identified: umami, the taste of monosodium glutamate (MSG), characteristic of protein-rich foods. Taste buds are believed to contain receptor molecules that trigger nerve signals when they encounter flavour-imparting molecules. The details of this system are still not understood. Each taste sensation may correspond to a fingerprint signal induced by the differential activation of the various taste receptors. E-Tongue works on this principle. It works by measuring dissolved compounds and taste substances in liquid samples (Giese, 2001). It contains four different chemical sensors. The sensors comprise very thin films of three polymers and a small molecule containing ruthenium ions. These materials are deposited onto gold electrodes hooked up to an electrical circuit. In a solution of flavorsome substances, such as sugar, salt quinine (bitter) and hydrochloric acid (sour), the thin sensing films absorb the dissolved substances. This alters the electrical behavior (the capacitance) of the electrodes in a measurable way. Each sensor responds differently to different tastes. A composite sensor that incorporates all four therefore produces an electronic fingerprint of the taste. The researchers combine these responses into a single data point on a graph. The position on the graph reflects the type of taste: sweet lies towards the top left, for example, sour towards the top right (Riul et al., 2002). Different beverages have a characteristic location on the graph. Coffee is low down around the middle, for instance. Some tastes that might be expected to differ only slightly, such as distilled and mineral water lie far apart on the graph and so can be clearly distinguished. E-Tongue –The Present


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Researchers at the University of Texas have developed an E-Tongue that they hope they will someday be able to taste the differences in a variety of liquids, from orange juice to blood. But can an E-Tongue mimic the sophisticated palates of wine tasters? Eventually, its developers say, it may come close. With wine, for example, the tongue changes colour depending on how sweet or sour the vintage is. They also plan to go beyond the four tastes of the human tongue and use the device to analyze such substances as blood or urine, or to test for poisons in water. Someday, says chemist Eric Anslyn, the tongue might speed up blood analysis by testing everything from cholesterol to medications in a person's bloodstream, all at the same time. But the developers have a way to go before achieving their vision. So far, the tongue can only tell the difference between white wine and white vinegar. Alpha M.O.S. exhibited the recently introduced Astree E-Tongue at the IFT annual Meeting and Food Expo in New Orleans, La. The Astree is designed for liquid product analysis and taste control. Advantages of E-Tongue The typical analysis time using the E-Tongue is about 3 min from when the sensors are introduced into the beaker containing the sample. It takes only 5 minutes for analysis and sensor cleaning. It has been proved that the instrument is so sensitive that it can response to as 10-2 molar of sucrose, caffeine, salt (NaCl), sour (HCl) and Umami (MSG) (Tan et al., 2001). Application of E-Tongue would be advantageous to analyze the taste of those toxic substances which human dare to taste due to toxicity. Successful application of E-Tongue may offer online monitor of taste and documentation, thereby permits better product process maintains. Therefore, E-Tongue may help the food processor to reduce wastage from poorly controlled processes and increased productivity. Since, E-Tongue readily tends itself to automation and computerization, monitoring taste quality can be incorporated into the manufacturing process. Another advantage is its versatility. E-Tongue being developed range from small, inexpensive, handhold devices e.g. those for periodic taste analysis goods for household purposed to sophisticated devices for contitinuous, on-line monitoring of taste quality. Eventually, E-Tongue will be inexpensive disposable units, placed on a roll of tape to be used quickly and easily. Application of E-Tongue permits many sorts of diverse sample to be examined. Once a protocol has been established, the instrument does not require highly skilled operators. Detectors in E-Tongue The detector consists of an array of seven different liquid cross-sensitive sensors. These detectors are selected on the basis of application, since sensitivity and selectivity are important for obtaining instrumental correlation. Upto 25 different sensors are commercially available. The sensors are made of silicon transistors with an organic coating that governs sensitivity and selectivity of each individual sensor.


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The proprietary coating is used to ascertain good repeatability, sensitivity and selectivity. The response (R) of E-Tongue mathematically represented as follows: R = f (SL, P), where SL corresponds to the liquid sensor sensitivity and selectivity and P corresponds to the liquid sample. E-Tongue seeks to measure the attributes, such as salty, sweet, bitter, sour, and savorless. The measurement consists of a potentiometric difference between each individual coated sensor and the Ag/AgCl reference electrode. The main part of E-Tongue is a set of potentiometric chemical sensors, applicable for liquid analysis Sensor arrays include different types of sensors: conventional ones, specially designed non-specific sensors with enhanced crosssensitivities or classical electrochemical electrodes are used depending on the task, sensor stability and/or cross sensitivity. Data Processing The second essential part of an E-Tongue is the data processing. Since the number of sensors in the array of an E-Tongue can reach 40, each of them producing a complex response in the multicomponent environment, a relevant multidimensional data processing must be performed. This is done by different pattern recognition methods such as Artificial Neural Networks (ANNs) or multivariate calibration tools. Each method has its own advantages as well as drawbacks, which must be carefully considered to get reliable analytical results in food analysis. Pattern-Recognition System in E-Tongue The chemo metric package comprises various pattern-recognition analysis modules for evaluating the data recorded from the array of liquid sensors. The modules include principal component analysis (PCA), discrimination function analysis (DFA), Soft Independent Model Clam Analogy (SIMCA), and Partial Least Square (PLS) (Alpha M.OS, 2001b). The various pattern-recognition modules are utilized to achieve instrumental correlation to sensory tests that are conducted. On the basis of the objectives of analysis, different modules are used. For instance, PLS is utilized for quantitative analysis, where the objectives are to quantify a particular molecule of attribute. For qualitative analysis, SIMCA can be used for comparison to ensure good similarity of a new product to a gold standard. The modules of the ETongue are the same and/or very similar to those used for the E-Nose. Training of E-Tongue E-Tongue, like a human being, needs to be trained with a correctly selected sample set to ensure good recognition and reproducibility. E-Tongue, in fact, seems to be black box; it knows nothing until it is taught Alpha M.O.S. (2000) suggested the procedure for training, model building, and validation for the instrument.


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Operation of an E-Tongue The auto-sampler allows 15 samples to be evaluated automatically, once the sample has been prepared. Preparation of samples typically involves filling the 100 ml beakers to three-fourths full. No other sample preparation is required. One beaker position is reversed for cleaning the sensor array following analysis of each individual sample. The auto-sampler also includes fluidic pumps for cleaning out the beaker for sensor rising when needed. Cooling to 2 to 4°C also ensures that there is limited sample change during analysis cycle. Analysis of sample is followed by a wash cycle to ensure that there is no carryover of sample to the next analysis and also to ensure good reproducibility. Typically, upto five replicate measurements are made for each sample. Correlation between E-Tongue Output and Human Perception A good agreement was observed for coffee, wine and soft drinks. That is why "artificial tasting" of beverages and foodstuffs based on sensor arrays and multivariate data processing seems to be a highly interesting emerging field. The performance of E-Tongue is presented in Table-1. Table-1 Attributes

Qualitative Analysis

Quantitative Performance

Typical sensor array size

20 - 40 sensors

10-30 sensors

Typical number of measuring sessions

4-8

12 - 50

Number of measurements within each measuring session

3

3 - 10

Examples

Discrimination of different types of beverages. Discrimination of different coffees by name, Discrimination of orange juices by their quality.

Classification of the different coffees depending on acidity, Glycerol rate in wine samples, Determination of components in model blood plasma.

Applications of E-Tongue


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E-Tongue has a multitude potential application, which includes its uses in quality control laboratory in space station and in medicine/body functions. A new hand-held E-Tongue promises to give accurate and reliable taste measurements for companies currently relying on human tasters for their quality control of wine, tea, coffee, mineral water and other foods. E-Tongue can sense low levels of impurities in water. It can discriminate between Cabernet Sauvignons of the same year from two different wineries, and between those from the same winery but different years. It can also spot molecules such as sugar and salt at concentrations too low for human detection. The electronic fingerprint allows the scientists to predict what a particular solution will taste like. Martin Taylor of the University of Wales at Bangor has anticipated that the device will probably be able to discriminate the umami taste too, giving it a refined palate for sushi. The food and beverage industries may want to use E-Tongue to develop a digital library of tastes proven to be popular with consumers, or to monitor the flavours of existing products. The E-Tongue has been designed to replace human tasters. E-tongue can also "taste" cholesterol levels in blood, cocaine in urine, or toxins in water. An "E-Tongue" for monitoring water quality on spacecraft and planetary habitats. Researchers hope E-Tongue can be used by industry to ensure that beverages coming off assembly lines are uniform in flavour. Quality control for beverages is one way the E-Tongue can be used. This first-generation E-Tongue has the ability to assay solution content for Ca2+, Ce3+, H+, and fructose using colorimetric indicators that are covalently linked to polyethylene glycol-polystyrene resin beads. E-Tongue can be applied for quantitative analysis and recognition (identification, classification) of a very wide range of liquids on aqueous and waterorganic basis. The most promising are the perspectives of E- Tongue application for quality control and identification of the conformity to standards for different food stuffs - juices, coffee, beer, wine, spirits, etc. Also the system can be successfully utilized in complicated tasks of industrial and environmental analysis, such as determination of the composition of groundwater in the abandoned uranium mines. There are several laboratory prototypes of E- Tongue, which have been constantly used for several years in the Laboratory of Chemical Sensors of St Petersburg University. Mobile versions of the system for special applications are being developed. Surprisingly this technology has created interest in vastly different areas. Besides the food industry, environmental and tourist industries want to incorporate it into hand-held monitors for feedback about local air and water. And there are huge markets in biomedical applications. E-Tongue can play a significant role in product development and quality assurance/quality control. E-Tongue measurement of taste and non-volatile components of food and beverages can be carried out easily to complement the headspace aroma/odor analyses, thereby adding a new dimension to the instrumental correlation of human perception. Like E-Nose, ETongue can be used for several purposes, including sample analysis, quality control,


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and product matching (Madsen and Grypa, 2000). Regarding food industry and related processes, E-Tongue has already been successful in the following fields. In the brewing industry, E-Tongue can be used to monitor batch-to-batch variation of the beers following the brewing process. E-Tongue allows product conformity testing, taste default detection, origin identification (Giese, 2001). The objective of the instrument is to complement the E-Nose and more important, allow the food and beverage industry to cover a large proportion of the sensory perception of consumers-in essence, covering both aroma/odour and taste (Tan et al., 2001). For orange juice and apple juice, E-Tongue will more typically measure the non-volatile components, including chemical molecules responsible for sweetness, bitterness, saltiness, and sourness (Tan et al., 2001). This instrument has also been used to detect off-flavour in beer, as in a pale ale lager containing too high a concentration of dimethyl sulfide (DMS), formed from a malt-derived precursor during wort production or by contaminant bacteria during fermentation (Tan et al., 2001). An extremely important taste attribute of beer is its bitterness. A range of beers has also been analyzed using E-Tongue. Result shows the good linearity of quantification of BU (Bitterness Unit) using PLS. E-Tongue has also been used for the analysis of quality of high-fructose corn syrup to detect some taint compounds responsible for the off-flavours, such as fish taste/flavour formed by microbiological oxidation of protein residues and other taste/odour descriptors including fruity, astringent, SO2, salty, corn-caramel, and moldy. Bleibaum et al. (2001) tested a series of nine 100 % apple juices, including a three-apple blend, vitamin-C fortified apple/pear juice, and an apple cider using ETongue. There are numerous fields in the food industry where E-Tongue may prove beneficial in food processing, with in principle and practice. Quality management is of utmost importance in the food industry, especially since the in guess of the good quality assurance Programme. Application of E-Tongue would allow the taste quality of a food to be monitored continuously from the raw material stage right through to final product. In recent years, E-Tongue finds food and beverage industry as the challenging environment for its routinely application in taste control and analysis. E-Tongue-The Tomorrow The technology is projected to save millions of rupees, as it becomes an integral part of industrial process quality control systems. Once established in the pharmaceutical industry, Scientists have planned to expand and apply the instrument to the clinical diagnostic market, developing equipment that will help physicians diagnose patients at the bedside. By saving time at the point of care, it will save lives. That's the whole point of commercializing this technology. In the epoch of miniaturization, scientists lead their concentration to develop E-Tongue of tomorrow based on a ‘single chip’. Scientists are thinking that medical diagnosis and food


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quality amassment will be the most challenging application field for E-Tongue. It may be applied to solve some environmental problems such as analyzing hazardous wastes of factory and tape as well as ground water quality. The application of E-Tongue would include the inspection of quality of fish, meat and fermented products during household storage or commercial storage period. Conclusion For many years, assessment of sensory quality of food has been based upon the traditional method i.e. application of human senses. As new food processing lines are developed, computer control will became an increasingly important part of factory operation. Sensor technology has offered the food industry a new, rapid type of monitoring and measuring device for taste analysis of foods i.e., E-Tongue, whose speed, sensitivity stability and ease of use exceed the efficiency of human taster. The successful miniaturization of sensors would advance the capability of E-Tongue to monitor and analyze several taste analytes using ‘single chip’ instrument. In the food and beverage industry in the western countries, E-Tongue has evolved with a great deal of fanfare, which may change the scenario of the present food industry where the evaluation of the product is till relied upon human senses, such as smell, taste etc. While the application of E-Tongue will no qualm present a radical revolution in quality control of foods providing the food industry with a great opportunity to exploit this novel technology, it will face a dual challenge involved in identifying and progressing the technology to capitalize on these. Some day is coming when you wouldn’t need to wait at the door of your panel member with a tray containing a cube of cheese for sensory evaluation, an E-Tongue fitted online would automatically analyse and document the product quality batch by batch or someday household refrigerator would automatically alert your brisk housewives that your Quarg cheese gets soured, which you put since last Deepawali.

References Alpha MOS. (2001a). Astree electronic tongue user manual. Toulouse, France. Alpha MOS. ( 2001b). Astree sensor technical note. Toulouse, France. Alpha MOS. ( 2001c). Special newsletter “Basell Interview”. Toulouse, France. Alpha MOS. (2000). FOX2000/3000/4000 Electronic Nose advanced manual. Toulouse, France. Bleibaum, R.N., Stone, H., Isz, S, Labreche, S., Saint Martin, E., and Tan, T.T. (2001). Comparison of sensory and consumer results with Electronic Nose and Tongue sensors for apple juices. Submitted for publication (http//www.google.com/). Giese. J. (2001). Electronic Tongues, Noses and much more. Food Technology, 55(5): 74-81


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Kanawjia, S. K. and Makhal, S. (2007) E-Tongue: a device for sensory evaluation of foods. CAS Lecture Compendium: Computer applications in food and dairy processing, DT Div., NDRI, Karnal. Madsen M. and Grypa, R. (2000). Spices flavour systems and the Electronic Nose. Food Technology, 54 (3): 44-46. Riul, A. et al. (2002). Artificial taste sensor: efficient combination of sensors made from Langmuir-Blodgett films of conducting polymers and a ruthenium complex and self-assembled films of an azobenzene-containing polymer. Langmuir, 18: 239 – 245. Tan, T.; Lucas, Q.; Moy, L; Gardner, J.W. and Bartlett, P.N. (1995). The Electronic Nose – A new instrument for sensing vapours. LC-GC 1NT, 8(4): 218-225.


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ROLE OF PACKAGING MATERIALS IN ENHANCING

SENSORY QUALITY OF DAIRY PRODUCTS

Dr. G.K. Goyal Principal Scientist Dairy Technology Division NDRI, Karnal 1.0. Introduction In modern times packaging has become an integral part of processing in the dairy industry. Package is the gateway to know a product. Packaging is also brand ambassador of a product. Packaging is technology of protecting products from the adverse effects of the environment. It is a medium for safe delivery of the products from the centre of production to the point of consumption.. A product is often identified by the package in which it is served (Goyal and Tanweer Alam, 2004). The package must ensure the same high quality of the product to the consumer. Packaging of products materially contributes to trade promotion and conserves valuable manpower and raw materials. The packaging industry is growing at a much higher rate in developing countries. Projected growth rate of demand and consumption for packaging in India is 10% to 12 % (Anon, 2005a). 2.0. Functions of Package The packages mainly perform three functions viz. to contain, to protect and to inform / sell the product. It is essential to know the nature and composition of the product, its desired shelf-life under specified conditions of storage in terms of light, temperature, humidity, presence of oxygen, the types and causes of deterioration including mechanical stress, the product may undergo during handling and storage. The selected packaging materials for dairy products should have following properties: • • • • • • • • • •

It should not impart its own odour to the product. It should be inert to food and must be non- toxic. It must protect from moisture, oxygen, and light Convenient Temper proof Printable Machinabe Point of sale impact Differentiability Economic


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The package not only protects the product but also gives information about the contents, storage conditions, methods of use, date of manufacture expiry date, price and nutritional consideratios. There are many more peculiarities, which could be identified under the following headings for, determining the packaging of dairy products. (i) (ii) (iii)

Product range Market Consumer needs

(iii)

Operating margins

3.0. Traditional Milk Products: It is estimated that nearly half of the total milk production in India is utilized for the manufacture of a range of traditional milk products viz., fat rich (ghee), heat desiccated (Khoa and Khoa based sweets, Rabri, Basundi, etc.), acid coagulated (Paneer, Chhana and Chhana based sweets), fermented (Dahi, Mishti dahi, Shrikhand), cereal based (Kheer, Payasam etc.) and frozen (Kulfi) products. Most of these products, except 10 –15% of total ghee production, are produced by unorganised sector (Halwais) using labour and energy intensive batch processes, resulting into large variations in their qualities. The shelf life of traditional dairy products is generally low and does not commensurate with the principles involved in their manufacture. One of the reasons for poor shelf life is either no packaging or inadequate packaging of traditional dairy products mainly post manufacturing, due to unhygienic conditions in production, packaging and storage areas. A number of surveys conducted on the market quality of indigenous milk products have revealed alarmingly high incidence of microbial contamination, besides large variations in chemical composition, flavour and texture. Most of the indigenous milk products have high water activity leading to rapid deterioration at ambient temperatures. Further, food products exposed to different environmental conditions without packaging get contaminated easily with moulds and bacteria. Improperly packaged foods undergo many flavour and textural changes during transportation and marketing. Lack of knowledge about the nature of food products and their compatibility with the packaging material may forfeit the purpose and lead to escalation of cost (Goyal and Gupta, 1989; Goyal and Rajorhia, 1991). 3.1. Milk Sweets: It is common practice to keep the milk-based sweets in open metal trays. On demand, the items are weighed and placed in ordinary paper bags or kept on dhak leaves and given to the consumers. At the most, some halwais or shopkeepers wrap sweets in glassine or grease-proof paper and sell them in duplex board boxes. Also gulabjamun, which is kept soaked in sugar syrup, has no better packaging for local consumption, though it is canned for export purposes.


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3.1.1.0. Khoa based sweets: Some of the khoa based sweets namely ‘peda’, ‘Carrot halwa’, ‘Kalakand’, ‘Burfi’, ‘Gulabjamun’, etc. are very common. Table : Packaging trend of khoa based sweets (Tanweer Alam et al., 2005) Product

Packaging material

1. Peda

Paperboard carton with paper lining, paper bags, dhak leaves, plastic box

2. Carrot halwa

Paperboard carton, plastic box

3. Kalakand

Paperboard carton, dhak leaves, plastic box

4. Burfi

Paperboard carton, paper bags, dhak leaves, plastic box

Burfi, Peda and Kalakand: Amongst the several khoa-based sweets, burfi and peda occupy most dominating place in terms of popularity and market demand. These are mostly packaged in paper cartons or duplex board boxes with or without butter paper lining. The traditional packages do not provide sufficient protection to milk sweets from atmospheric contamination and unhygienic handling and thus susceptible to become dry, hard and mouldy and develop off flavours. Also the product packed in these wrappers / packages are not suitable for distant transportation and outstation retail sale or sale through super markets because they lack necessary mechanical and protective properties. Tin containers can be used but their cost is prohibitive. Only recently, some of the reputed manufacturers of these sweets have started packaging burfi and peda in HDPE/polypropylene boxes and cartons of 500g and 1 kg size. The modern flexible polyfilms and laminates offer alternate choice. The chemical composition of the sweet, the transportation hazards, and the period of storage under specified conditions of temperature and humidity are the major factors, which should largely decide the type of packaging materials. The common types of spoilage in burfi, peda and kalakand can be significantly delayed or altogether prevented by using flexible packages. (Pal, 2003; Tanweer Alam et al., 2005). i) Prevention of body and texture defect: Burfi contains moisture content ranging from 4.3 to 15.1%, while peda contains 4.2 to 22.3% moisture, and kalakand contains 16 to 28% moisture. At these moisture levels, the sweets have unique texture and typical chewing properties. For storage of burfi, an optimum RH of 70% is recommended. High RH and low RH make the product moist, pasty and hard, respectively. The choice may be from HDPE, PP, MXXT, polycel or other suitable combinations. This will prevent the ingress of


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moisture into the product and prevent the products becoming pasty under humid conditions. ii) Prevention of rancid and oxidized flavours: Khoa based sweets are quite rich in milk fat, and hence susceptible to rancidity and oxidative changes during storage. Proper packaging can play a key role in preventing the rancidity. Among the factors, which accelerate rancidity, light is most effective. Hence, this should be prevented by using packaging materials having reflecting pigments, denser films. Packaging materials which have very good oxygen barrier properties such as MST cellulose, MXXT, metallized polyester / poly, 5-layer co- extruded films, laminates having Al – foil are recommended for preventing oxidative deterioration. Vacuum packaging of the products also enhances the shelf life to a great extent. (iii) Prevention of discolouration and absorption of foreign odours: Burfi, peda and kalakand often lose their original colour and appearance during storage. Light induced oxidation may lead to loss of colour intensity. Maillard type browning – a common storage defect of milk sweets, is also accelerated by exposure to light and moisture. These fat rich dairy products quickly absorb foreign odours and rapidly lose their inherent delicate flavour. It is extremely important that these products are packed in such materials which can stop the two-way traffic of odours / gases in the products in order to preserve their original colour and flavour. Packaging material should also be grease resistant in order to minimise seepage of fat. 3.1.2.0. Channa based sweets: Channa based sweets like sandesh, rasogolla, etc. are extremely popular in the eastern and north eastern regions of the country. Sandesh is generally packaged in paperboard cartons with a paper lining, ordinary paper bags and Dhak leaves. The rosogolla is packaged in tinplate cans, or in paperboards, Dhak leaves, Kulhads(earthen pots) etc. Canning of rosogolla is expensive and the other methods of packaging are unhygienic, inconvenient and unsuitable for outstation retail sales (Goyal and Rajorhia, 1991). 3.1.3.0. Gulabjamun and Rosogolla: These sweets need to be saved from light, oxygen, ingress or egress of moisture, yeasts and moulds. Gulabjamun is a khoa based sweet while Rosogolla is prepared from chhana. The similarity between the two is based on their shape, texture and method of storage. Both are spherical in shape, spongy, porous and kept in sugar syrup. Their shape and porosity attributes are very critical and have to be maintained till the product reaches to the consumer. On an average, they contain about 40% moisture and 50% sugar. Fat content in Gulabjamun is more than Rosogolla. Yeast and mould growth is a more common problem associated with yeasty / fruity flavour


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defects during storage in both the sweets. Since the body and texture of rosogolla is very delicate and it has to be preserved in sugar syrup, it is invariably packaged in lacquered tin cans of 500g and 1kg respectively. The proportion of rosogolla and syrup is kept 40:60 and product stays in good condition for more than 6 months at ambient conditions, because hot filling (at about 90ºC) technique is adopted. Gulabjamun is largely packaged without syrup in paper cartons or plastic boxes like burfi and peda. Though lacquered tin can is the most suitable packaging material for rosogolla and gulabjamun, but it is very expensive. Hence, there is a need to pack these products in composite cans made of plastic and laminated with a PP – Al foil material. (Pal, 2003; Goyal and Gupta, 1989). 3.1.4.0. Paneer: Paneer is commonly packaged in PE bags. Recently, some organizations have started its vacuum packaging. In order to increase its shelf life significantly by employing the modified atmosphere packaging (MAP), the research work has been done at Dairy Technology Division, NDRI, Karnal. 3.1.5.0. Dahi and Yoghurt: Dahi and yoghurt are mostly packed in PS cups, but they cause pollution besides not being health-friendly. Hence, efforts are on to switch the packaging of these products from PS cups to earthen pots. 3.1.6.0. Ghee: Majority of the dairies pack ghee in lacquered or unlacquered tin cans of various capacities ranging from 250gm to 15kg. Tin cans protect the product well against tampering and during transportation to far off places without significant wastage. The most common and serious deterioration in ghee is the development of rancid flavour, caused by the formation of volatile compounds, which give unpleasant odour even in micro quantities. The modern packaging plays a vital role in delaying the onset of this defect. The packaging material should also possess good water vapour barrier properties. High-density polyethylene (HDPE) and polypropylene (PP) are known to have low water vapour transmission rates (WVTR), and are easily available and cheap. If such films are laminated to other suitable basic packaging materials, one can get almost negligible value for WVTR, which would be ideal. The package to be selected should show sufficient tensile strength, elongation, tear resistance and burst strength, besides overall good mechanical strength. The packaging of ghee can also be done in polymer coated cellophane, polyester, nylon – 6, or food grade PVC and their laminates. 3.1.7.0. Dried Milk Products: Gulabjamun mix, kheer mix and kulfi mix:


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Consumer packages for these products include: sachets and flexibles (having high barrier properties like metalized polyester etc) kept in cartons.

4.0 Conclusion Due to appearance of Mall-culture, revolutionary changes are taking place at a very fast speed in packaging of food products. It is expected that new forms of packaging material such as roll wraps, pouches, cartons, PP – trays covered with transparent coloured films of MXXT or such other films are likely to appear on the market place for packaging of dairy products. Further, with a view to enhance the sensory quality vis-à-vis shelf life, thermal processing of certain milk products right in the packages is being successfully attempted. Although, the country has made significant advances in the field of packaging material technology, the dairy packaging machineries have not been developed. Hence, there is alarming need that Dairy Engineers develop such packaging machines, which could be commercially used by medium sized milk sweet manufactures throughout the country. 5.0 Reference Anon (2005a). Indian packaging sector, http//www. ciionline. org/news//htp Anon (2005b). www.packagingindustry.com Anon (2006).. Growth of Indian Dairy sector, http//www. ciionline. org/news//htp Goyal, G.K. and Gupta, S.K. (1989). Packaging of dairy products – a review, Beverage & Food World, 16(1): 42-46 Goyal, G.K. and Rajorhia, G.S. (1991). Role of modern packaging in marketing of Indigenous dairy products. Indian Food Industry, 10(4): 32-34. Pal, D. (2003). Packaging of traditional Indian dairy products: Present status and future prospects, compendium of lectures of 15th CAS course on ‘Advances in packaging of dairy and food products’ organized at NDRI, Karnal from 13th Feb. to 5th Mar 2003,pp 95-101. Tanweer Alam, Goyal, G. K. and Broadway, A.A. (2005). Packaging trends in dairy Industry. In: Indian Dairy Industry, volume I, Published by Dr. Chawla Dairy Information Centre (P). Ltd, New Delhi, pp 180-185.


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CONSUMER ACCEPTANCE STUDIES

Dr. Latha Sabikhi Senior Scientist Dairy Technology Division NDRI, Karnal 1.

Introduction

Consumers are the starting and end point of marketing management in any field. Food being an unavoidable commodity, consumer acceptance of food is a vital reality in food companies. The core of Consumer Acceptance Studies (CAS) pertains to the decision-making process of consumers with respect to food choice, as well as to the factors impacting on this decision-making process. Food companies analyse their consumer’s needs and wants, which are consequently translated into product specifications, product attributes, product development, price, promotion or communication and a specific retail or distribution format. Consumer acceptance of new technologies, novel products and the impact of personal characteristics on product acceptance is a specific field of study in current product management programmes. 2.

What are Consumer Acceptance Studies?

Well-structured CAS in the food arena deals with the changes in food consumption in contemporary society and the developments of food practices in everyday life. Consumers not only make buying decisions but are also citizens living as a part of the whole food system. As citizen-consumers people interact in various ways with other persons in the food system, such as food producers, manufacturers, retailers, authorities and policy-makers. From this perspective, consumers are seen as part of the food system that takes shape and develops in the context of societal changes both nationally and internationally. Eating is a complex activity of diverse developments relating to the social and individual aspects of eating, environmental and economic pressures, global and local inequalities in economic and social resources, technological developments in food production and the increasing concern about the healthiness of modern eating habits. Thus, modern CAS are generally divided into two areas, a) views on food quality and b) food production, consumption and food habits. The first of these covers studies relating to consumer aspects of developing the quality of foods, buying food, developing the responsibility in the food chain and advancing the consumer perspective in the use of health claims in food marketing. The second area focuses on changes in food practices now and in the future, paying particular attention to the


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environmental, social and cultural sustainability of food production and consumption. It also deals with the consumers’ understanding and practices of healthy eating. 3.

CAS-Related Features in Food Science

The consumers’ perspectives, ideas and expectations concerning foods, food production and practices of eating must be improved before conducting food acceptance studies. Periodic training programmes are sometimes necessary to introduce the stakeholders to the different aspects of food tasting. Sensory properties such as flavour and texture play a major role in consumer perceptions of food product quality. The mouth-feel and other textural and sensory properties of food are an essential component of its perceived quality. The significance of textural properties has further increased with the trend towards low-fat, low-calorie and low-additive content products. Food structure is particularly important in baking, dairy and processed meat products. Traditionally, food structure has been improved by using ingredients such as emulsifiers or thickeners. However, consumers tend to take a rather negative view of many of these ingredients. The goal of consumer studies is to assess the consumer’s and food industry’s perception towards novel technologies and ingredients. They may be presented with existing food technologies such as food additives, genetic modification, irradiation, vacuum packing, pasteurization, microwave ovens and canning, as well as technologies that are conventionally non-food-related as use of magnetic waves, rays and computer-aided evaluation programmes. The survey then asks participants to indicate, in their own words, which technologies concern them and why. 4.

Consumer Attitude

Consumer attitudes are of profound importance when new technologies are developed and implemented into food production. Consumers are not usually aware of details of food production. However, they may form attitudes to certain food production technologies, including use of new ingredients, when they become confronted with information about it. These attitudes may prevent them from buying products where these technologies/ ingredients have been used. The way in which these skeptical attitudes affect the intentions to buy products produced using novel technologies and ingredients, particularly the possibility of a negative attitude towards to the production method with additional sensory benefits, is presently not wellunderstood. There are reports that CAS has proved to be an asset for ingredient development work. While the attitudes towards the use of several novel ingredients in food production are fairly neutral, those towards use of genetic engineering in food production and ingredients produced by use of gene technology are more negative. Studies also revealed that the acceptance of the technology is closely linked to the relevance of the functionalities of the products as well as the cost vs. benefit analyses. Consumers often changed their attitudes towards new technologies/ products/


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ingredients after actually tasting the product when compared to those who did not taste the products. A study conducted at the University of Guelph (Canada) revealed that perceived risks and benefits is another important factor that influences how consumers receive new food technologies. Consumers are willing to take a risk if they receive greater benefits such as improved health, better quality or lower price. If the benefits outweigh the perceived risks, consumers are more likely to buy into the product 5.

The Process

To initiate CAS, a group is identified as a sample of the entire group of potential consumers. The sample must be as close and as representative of the entire population as possible. A questionnaire or score card is formulated in accordance with the product/ process/ ingredient on which the CAS is conducted. Each member of the study group is given the product and the schedule of questions. If any special instructions are to be given on the manner of testing the product or filling the schedule, these are also handed out. A reasonable period of time is given to the consumers to test the product and fill answer the questions on the schedule. The filled schedules are collected after the stipulated time. This is a very important step, as uncollected questionnaires result in waste if efforts besides tarnishing the image and the integrity of the firm. The data collected is tabulated and subjected to appropriate statistical analysis. The interpretation is a key to the changes/ innovations to be introduced into the practice. 6.

Conclusion

Consumer acceptance studies are currently the norm and practice in western countries. In the emerging countries, such studies involving the most vulnerable consumers on the lowest incomes are still relatively under-reported. Programmes seeking to introduce new products, and those who are involved in their promotion and marketing, must acquire knowledge about consumer acceptance and sensory testing in order to ensure these programmes are more effective.

7.

Some Useful Websites ftp://ftp.cordis.europa.eu/pub/food/docs/consumer-crossenz.pdf http://www.kuluttajatutkimuskeskus.fi/index.phtml?l=en&s=150 www.uoguelph.ca/news/2005/08/study_delves_in.html


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CHEMISTRY OF FLAVOUR DEVELOPMENT IN CHEESE Dr. Sumit Arora Senior Scientist Dairy Chemistry Division NDRI, Karnal - 132001

Cheese is the generic name for a group of fermented milk based food products. More than 500 varieties of cheeses are listed by the International Dairy Federation (IDF 1982), and numerous minor and/or local varieties also exist (Fox 1987). The flavor profiles of cheeses are complex and variety- and type-specific. This was realized back in the 1950s, when Mulder (1952) and Kosikowski and Mocquot (1958) proposed the “component balance” theory. According to this theory, cheese flavor is the result of the correct balance and concentration of a wide variety of volatile flavor compounds. According to Olson (1990) “There is a cheese for every taste-preference and a taste-preference for every cheese”. Unlike many processed food products for which stability is the key criterion, cheese is a biochemically dynamic product and undergoes significant changes during its ripening period. Freshly-made curds of various cheese varieties have bland, and largely similar, flavours and it is during the ripening period that flavour compounds are produced which are characteristic of each variety. Originally, it was thought that cheese flavour resulted from a single compound or class of compounds. While this is largely true for blue-mould varieties (whose flavour is dominated by alkan-2- ones), it is now generally accepted that the flavour of most cheeses results from the combination of a large number of sapid compounds present in the correct ratios and concentrations (Bosset and Gauch 1993; Mulder 1952; Kosikowski and Mocquot 1958). The volatile flavor compounds in cheese originate from degradation of the major milk constituents; namely lactose, citrate, milk lipids, and milk proteins (collectively called caseins) during ripening which, depending on the variety, can be a few weeks to more than 2 years long.

Biochemical reactions during manufacture and ripening of cheese Cheese ripening is a slow process, involving a concerted series of microbiological, biochemical and chemical reactions. The characteristic flavor, aroma, texture, and appearance of individual cheese varieties develop during ripening. These changes are predetermined by the manufacturing process: (a) composition, especially moisture, pH and salt, and (b) microflora, starter, and especially nonstarter microflora and adjunct starter (that is, microorganisms added to cheese milk for purposes other than acidification) (Gilles and Lawrence 1973). The ripening of cheese Sensory and Related Techniques for Evaluation of Dairy Foods

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involves 3 primary biochemical processes (Fig 1) processes— glycolysis, lipolysis, and proteolysis—the relative importance of which depends on the variety (Fox et al. 1994).

Fig 1. Biochemical pathways leading to the formation of flavour compounds (Marilley and Casey 2004)

These primary changes are followed and overlapped by a host of secondary catabolic changes, including deamination, decarboxylation and desulfurylation of amino acids, β-oxidation of fatty acids and even some synthetic changes; that is, esterification (Fox 1993). The above-mentioned primary reactions are mainly responsible for the basic textural changes that occur in cheese curd during ripening, and are also largely responsible for the basic flavor of cheese. However, the secondary transformations are mainly responsible for the finer aspects of cheese flavor and modify cheese texture. The compounds listed in Table 1 are present in most, if not all, cheese varieties. The concentration and proportions of these compounds are characteristic of the variety and are responsible for individuality. These complex biochemical changes occur through the catalytic action of the following agents: • Coagulant • Indigenous milk enzymes, especially proteinase, lipase, and phosphatases


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• Starter bacteria and their enzymes • Secondary microflora and their enzymes The biochemistry of the primary events in cheese ripening is now fairly well characterized, but the secondary events are understood only in general terms. Table 1: Flavour compounds generated from the 3 principle components during ripening of cheese

(Singh et al. 2003) Lactose and citrate During Cheddar cheese manufacture, mesophilic starter bacteria ferment lactose to (mainly L+) lactic acid. In the case of Cheddar-type cheeses, most of the lactic acid is produced in the vat before salting and molding. Even after losing ~98% of the total milk lactose in the whey as lactose or lactate, the cheese curd still contains 0.8 to 1.5% lactose at the end of manufacture (Huffman and Kristoffersen 1984). The pH decreases after salting, presumably due to the action of starter, at S/M levels < 5.0%, but at high values of S/M, starter activity decreases abruptly (Fox et al. 1990) and the pH remains high. The quality grade assigned to the cheese also decreases sharply at S/M levels > 5.0% (Lawrence and Gilles 1982). Lactose is hydrolysed by starter cultures which produce glucose and galactose (galactose-6-P for lactococci). Glucose is then oxidised to pyruvate by the Emden-Meyerhof pathway of glycolysis. Galactose is converted by galactose-positive starter bacteria and leuconostocs through the Leloir pathway to glucose- 6-P and by lactococci through the tagatose pathway to glyceraldehyde-3-P (Cogan and Hill 1993). Pyruvate is a starting material for the formation of short-chain flavour compounds such as diacetyl, acetoin, acetate, acetaldehyde and ethanol (Cogan and Hill 1993; Escamilla-Hurtado et al. 1996; Henriksen and Nilsson 2001; Syu 2001; Melchiorsen et al. 2002). Bovine milk contains relatively low levels of citrate (~8 mM). Approximately 90% of the citrate in milk is soluble and most is lost in the whey; however, the concentration of citrate in the aqueous phase of cheese is ~3 times that in whey (Fryer et al. 1970), presumably reflecting the concentration of colloidal citrate. Cheddar


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cheese contains 0.2 to 0.5% (w/w) citrate which is not metabolized by Lc. lactis ssp. lactis or ssp. cremoris, but is metabolized by Lc. lactis biovar diacetylactis and Leuconostoc spp, with the production of diacetyl and CO2. Due to CO2 production, citrate metabolism is responsible for the characteristic eyes in Dutch-type cheeses. Diacetyl and acetate produced from citrate contribute to the flavor of Dutch-type and Cheddar cheeses (Aston and Dulley 1982; Manning 1979a, 1979b). Citrate is metabolised to produce acetolactate, diacetyl and acetoin (Cogan and Hill 1993; de Figueroa et al. 2000, 2001). However, thermophilic starter bacteria are usually citratenegative (Cogan and Hill, 1993). The principal flavor compounds produced from metabolism of citrate are acetate, diacetyl, acetoin, and 2, 3-butandiol (Cogan 1995). Diacetyl is usually produced in small amounts, but acetoin is generally produced in much higher concentration (10 to 50 fold higher than diacetyl concentration). Acetate is produced from citrate in equimolar concentrations.

Milk fat Milk fat is an essential prerequisite to flavour development (Foda et al. 1974). As in all high-fat foods, lipids present in cheese can undergo oxidative or hydrolytic degradation. Because of the negative oxidation - reduction potential of cheese, oxidation of cheese lipids is probably limited; but the extent to which it occurs and its contribution (if any) to cheese flavour development has received little attention (Fox et al. 1982). Enzymatic hydrolysis of triglycerides to fatty acids and glycerol, monoor diglycerides (lipolysis) is, however, essential to flavour development in many cheese varieties. Milk fat contains high concentrations of short - and intermediatechain fatty acids which, when liberated by lipolysis, contribute directly to cheese flavour. The proportions of free C6:0 to C18:3 fatty acids in Cheddar cheese appear to be similar to those in milk fat, but free butyric acid (C4:0) occurs at a greater relative concentration in cheese than in milk fat, suggesting that butyrate is either selectively liberated by lipases present in Cheddar or that it is synthesized by the cheese microflora (Bills and Day 1964). The specificity of the lipase also influences the development of cheese flavour, since short-chain fatty acids (which have the greatest flavour impact) are generally found at the sn-3 position of triglycerides. Cheese pH also influences the flavour impact of FFA, since carboxylic acids and their salts are perceived differently. Lipolysis is particularly extensive in hard Italian varieties, surface bacterially-ripened (smear) cheeses and blue mould cheeses, and is essential to correct flavour development in these cheeses. Extensive lipolysis is considered undesirable in many internal, bacterially-ripened varieties such as Cheddar, Gouda and Swiss cheeses; high levels of fatty acids in these cheeses lead to rancidity. However, low concentrations of FFA contribute to the flavour of these cheeses, particularly when they are correctly balanced with the products of proteolysis or other reactions (Rychlik et al. 1997; Bosset and Gauch 1993). Lipolysis of milk triglycerides releases high concentrations


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of short- and intermediate-chain fatty acids (Bills and Day 1964). Short-chain fatty acids have a considerable flavour impact, but intensive lipolysis is undesirable in most cheese varieties because of the development of rancidity. Free fatty acids must be counter-balanced with other flavour compounds to develop an appreciated aroma (Bosset and Gauch 1993; Fox et al. 1995). Free fatty acids are substrates of enzymatic reactions yielding flavours. Oxidation and decarboxylation yield methyl ketones and secondary alcohols, and esterification of hydroxyl fatty acids produce lactones. Fatty acids react with alcohol groups to form esters, such as ethyl butanoate, ethyl hexanoate, ethyl acetate, ethyl octanoate, ethyl decanoate, and methyl hexanoate (McSweeney et al. 1997). Butyric acid concentrations found in cheeses are in part due to the hydrolytic activities of lipases (Dumont and Adda 1979; Fox et al. 1995). γ and δ- lactones have been identified in cheeses, particularly in Cheddar, where they have been considered as important for flavor (Wong et al. 1973). Lactones are cyclic esters resulting from the intramolecular esterification of hydroxy acids through the loss of water to form a ring structure. They possess a strong aroma which, although not specifically cheese-like, may be important in the overall cheese flavor impact. The accepted mechanism of formation of lactones in cheese presumes the release of hydroxy fatty acids, which are normal constituents of milk fat, followed by lactonization.

Milk Protein For the development of an acceptable cheese flavor, a well-balanced breakdown of the curd protein (that is, casein) into small peptides and amino acids is necessary (Thomas and Pritchard 1987; Visser 1993). These products of proteolysis themselves are known to contribute to flavor (Cliffe et al. 1993; Engels and Visser 1994) or act as precursors of flavor components during the actual formation of cheese flavor. During the manufacture and ripening of Cheddar cheese, a gradual decomposition of caseins occurs due to the combined action of various proteolytic enzymes. These generally include enzymes from the coagulant, milk, starter and nonstarter lactic acid bacteria, and secondary starter. Proteolysis directly contributes to cheese flavours by releasing peptides and amino acids. The correct pattern of proteolysis is generally considered to be a prerequisite for the development of the correct flavor of Cheddar cheese. Products of proteolysis per se (that is, peptides and free amino acids) probably are significant in cheese taste, at least to “background” flavor and some off-flavors, for example, bitterness, but are unlikely to contribute much to aroma. Compounds arising from the catabolism of free amino acids contribute directly to cheese taste and aroma. The total amount and composition of the amino acid mixture in cheese has long been used as an index of cheese ripening (Fox et al. 1995b). Amino acids are substrates for transamination, dehydrogenation, decarboxylation and reduction, producing a wide variety of flavour compounds such as phenylacetic acid, phenethanol, p-cresol, methane thiol, dimethyl disulphide, 3-


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methyl butyrate, 3-methyl butanal, 3- methyl butanol, 3-methyl-2-butanone, 2-methyl propionate, 2-methyl-1-propanal, 2-methyl butyrate and 2-methyl butanal. In lactococci, the 1st step in the degradation of amino acids is transamination (Gao and others 1997), leading to formation of α-keto acids (α -KA). Aromatic aminotransferase enzymes have been previously characterized from Lactococcus lactis subsp cremoris (Rijnen et al. 1999a) and Lactococcus lactis subsp lactis (Gao and Steele 1998). These enzymes initiated the degradation of Val, Leu, Ile, Phe, Tyr, Trp, and Met, all of which are known precursors of cheese flavor compounds. Inactivation of aminotransferase enzymes involved in the breakdown of amino acids by lactococci has been shown to reduce aroma formation during cheese ripening (Rijnen et al. 1999b). Ney (1981) reported α -keto acids corresponding to almost every amino acid in Cheddar cheese. α -keto-3-methyl butyric acid and α -keto-3-methyl valeric acid (Ney and Wirotma 1978) were shown to have an intense cheese-like odor. The volatile fraction of cheese has several sulfur-containing compounds such as methanethiol, methional, dimethyl sulfide, dimethyldisulfide, dimethyltrisulfide, dimethyltetrasulfide, carbonyl sulfide, and hydrogen sulfide (Urbach 1995; Weimer et al. 1999), and they contribute to the aroma of cheese (Milo and Reineccius 1997). Methanethiol has been associated with desirable Cheddar-type sulfur notes in good quality Cheddar cheese (Manning and More 1979; Price and Manning 1983). However, alone or in excess, methanethiol does not produce typical Cheddar cheese flavor (Weimer et al. 1999). The discussion shows that amino acid degradation plays a vital role in flavor development in Cheddar cheese. The final products of proteolysis are FAA, the concentrations of which depend on the cheese variety, and which have been used as indices of ripening (McSweeney and Fox 1997; Puchades 1989). The concentration of free amino acids (FAA) in cheese at any stage of ripening is the net result of the liberation of amino acids from casein and their transformation to catabolic products. The principal amino acids in Cheddar cheese are Glu, Leu, Arg, Lys, Phe and Ser (Wijesundera et al. 1998). Concentrations of amino acids generally increase during ripening, with the exception of Arg, the concentration of which is reported to decrease later in ripening (Puchades et al. 1989). The level of peptides and FAA soluble in cheese in 5% phosphotungstic acid (PTA) has been considered to be a reliable indicator of the rate of flavour development (Aston and Douglas 1983) and the composition of the amino acid fraction and the 309 relative proportions of individual amino acids are thought to be important for the development of the characteristic flavour (Broome 1990). However, the relative proportion of individual amino acids appears to be similar in many varieties, and increasing the concentration of FAA in cheese does not accelerate ripening or flavour intensity. Medium and small peptides and FAA contribute to the background flavour of most cheese varieties (Urbach 1995) and some individual peptides have ‘brothy’, ‘bitter’, ‘nutty’ and ‘sweet’ tastes. Fox and Wallace (1997) have suggested that flavour and the concentration of FAA could not be correlated, since different cheeses (e.g., Cheddar,


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Gouda and Edam) have very different flavours, although the concentration and relative proportions of FAA are generally similar. Bitterness and other off-flavours Bitterness in cheese is due mainly to hydrophobic peptides and is generally regarded as a defect, although bitter notes may contribute to the desirable flavour of mature cheese. Certain sequences in the caseins are particularly hydrophobic and, when excised by proteinases, can lead to bitterness. Low-fat cheeses have been reported to develop bitterness (Banks et al. 1992), although in full-fat cheese, a certain proportion of bitter peptides, being hydrophobic, are less likely to be perceived as being bitter, perhaps due to their partition into the fat phase. In addition to peptides, a number of other compounds can contribute to bitterness in cheese, including amino acids, amines, amides, substituted amides, long-chain ketones and some monoglycerides (Adda et al. 1982). The origin of ‘unclean’ and related flavours in Cheddar has been attributed to a number of Strecker-type compounds (Dunn and Lindsay 1985) including phenylacetaldehyde, phenylethanol, 3-methylbutanol, 2methylpropanol, phenol, and p-cresol. Off-flavours (rancidity) can be due to excessive or unbalanced lipolysis caused by lipases/esterases from starter or non-starter lactic acid bacteria, enzymes from psychrotrophs in the cheese milk, or indigenous milk lipoprotein lipase. References Adda, J., Gripon, J.C. and Vassal, L. 1982. The chemistry of flavour and texture generation in cheese, Food Chem. 9:115–129. Aston, J.W. and Dulley, J.R. 1982. Cheddar cheese flavor. Aust J Dairy Technol 37:59-64. Aston, J.W. and Douglas, K. 1983. The production of volatile sulphur compounds in Cheddar cheeses during accelerated ripening, Aust. J. Dairy Technol. 38:66–70. Banks, J., Muir, D.D., Brechany E.Y. and Law A.J.R. 1992. The production of low fat cheese, Proc. 3rd Cheese Symp., Moorepark, Fermoy, Co. Cork, Ireland, pp. 67–80. Bills, D.D. and Day, E.A. 1964. Determination of the major free fatty acids of Cheddar cheese, J. Dairy Sci. 47:733–738. Bosset, J. O. and Gauch, R. 1993. Comparison of the volatile flavour compounds of six European ‘AOC’ cheeses by using a new dynamic headspace GC-MS method, Int. Dairy J. 3:359–377. Broome, M.C., Krause, D.A. and Hickey, M.W.1990. The use of non-starter lactobacilli in Cheddar cheese manufacture, Aust. J. Dairy Technol. 45:67–73. Cogan, T.M. and Hill, C. 1993. Cheese starter cultures. In: Fox, P.F. (Ed.), Cheese: Chemistry, Physics and Microbiology, 2nd ed. Chapman & Hall, London, pp. 193– 255.


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Cogan T.M. 1995. Flavor production by dairy starter cultures. J Appl Bacteriol (Symposium Suppl.) 79:49S-64S. Cliffe, A.J., Marks, J.D. and Mulholland, F. 1993. Isolation and characterization of nonvolatile flavors from cheese: peptide profile of flavor fractions from Cheddar cheese, determined by reverse phase high-performance liquid chromatography. Intl Dairy J 3:379-87. de Figueroa, R., Alvarez, F., Pesce de Ruiz Holgado, A., Oliver, G. and Sesma, F. 2000. Citrate utilization by homo- and heterofermentative lactobacilli. Microbiol. Res. 154:313– 320. de Figueroa, R.M., Oliver, G., Benito de Cardenas, I.L. 2001. Influence of temperature on flavour compound production from citrate by Lactobacillus rhamnosus ATCC 7469. Microbiol. Res. 155:257– 262. Dumont, J.P. and Adda, J. 1979. Flavour formation in dairy products. In: Land, D.G., Nursten, H.E. (Eds.), Progress in Flavour Research. Aspen Publishers, New York, pp. 245–262. Dunn H.C. and Lindsay R.C. 1985. Evaluation of the role of microbial Streckerderived aroma compounds in unclean-type flavours of Cheddar cheese, J. Dairy Sci. 68:2859–2874. Engles, W.J.M and Visser, S. 1994. Isolation and comparative characterization of compounds that contribute to the flavor of different cheese types. Neth Milk Dairy J 48:127-40. Escamilla-Hurtado, M.L., Tomasini-Campocosio, A., Valde´s-Martı´- nez, S. and Soriano-Santos, J.1996. Diacetyl formation by lactic bacteria. Rev. Latinoam. Microbiol. 38:129– 137. Foda, F.A., Hammond, E.G., Reinbold, G.W. and Hotchkiss, D.K. 1974. Role of fat in flavor of Cheddar cheese. J. Dairy Sci. 57:1137– 1142. Fox P.F., Singh T.K. and McSweeney P.L H. 1982. Biogenesis of flavour compounds in cheese, in: Malin E.L., Tunick M.H. (Eds.), Chemistry of Structure/Function Relationships in Cheese, Plenum Press, New York, pp. 59–98. Fox, P.F. 1987. Cheese: an overview. In: Fox PF, editor. Cheese: chemistry, physics and microbiology. Vol 1. London, U.K.: Elsevier Applied Science. pp 1-32. Fox, P.F., Singh, T.K., McSweeney, P.L.H. 1994. Proteolysis in cheese during ripening. In: Varley J, Andrews AT, editors. Biochemistry of milk products. Cambridge, U.K.: Royal Society of Chemistry. pp 1-31. Fox, P.F. 1993. Cheese: an overview. In: Fox PF, editor. Cheese: chemistry, physics and microbiology. Vol 1. 2nd ed. London, U.K.: Chapman and Hall. pp 1-36. Fox, P.F., Singh, T.K. and McSweeney, P.L.H.1995. Biogenesis of flavour compounds in cheese. Adv. Exp. Med. 367:59–98.


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Fox, P.F., McSweeney, P.L.H and Singh, T.K. 1995b. Methods for assessing proteolysis in cheese during ripening. In: Malin EL, Tunick MH, editors. Chemistry of structure/ function relationships in cheese. Adv Exptl Med Biol. Vol. 367. New York, N.Y.: Plenum Press. pp 161-94. Fox P.F. and Wallace J.M.1997. Formation of flavour compounds, Adv. Appl. Microbiol. 45:17–85. Fryer, T.F., Sharpe, M.E. and Reiter, B. 1970. Utilization of milk citrate by lactic acid bacteria and blowing of film-wrapped cheese. J Dairy Res 37:17-28. Gao, S., Oh, D.H., Broadbent, J.R., Johnson, M.E., Weimer, B.C. and Steele, J.L. 1997. Aromatic amino acid catabolism by lactococci. Lait 77: 371-81. Gao, S. and Steele, J.L. 1998. Purification and characterization of oligomeric species of an aromatic amino acid aminotransferase from Lactococcus lactis subsp lactis S3. J Food Biochem 22:197-211 Gilles, J. and Lawrence, R.C. 1973. The assessment of Cheddar cheese quality by compositional analysis. NZ J Dairy Sci Technol 8:148-51. Henriksen, C.M. and Nilsson, D. 2001. Redirection of pyruvate catabolism in Lactococcus lactis by selection of mutants with additional growth requirements. Appl. Microbiol. Biotechnol. 56:767– 775. Huffman, L.M. and Kristoffersen, T. 1984. Role of lactose in Cheddar cheese manufacturing and ripening. NZ J Dairy Sci Technol 19:151-62. IDF. 1982. International Dairy Federation. Catalogue of cheese. Brussels, Belgium: Intl Dairy Federation. Kosikowski, F.V. and Mocquot, G. 1958. Advances in cheese technology. FAO Agric Stud Nr 38. Rome, Italy: Food and Agriculture Organization [FAO]. pp 15. Lawrence, R.C. and Gilles, J. 1982. Factors that determine the pH of young Cheddar cheese. NZ J Dairy Sci Technol 17:1-14. Manning, D.J. 1979a. Chemical production of essential Cheddar cheese flavor compounds. J Dairy Res 46:531-7. Manning, D.J. 1979b. Cheddar cheese flavor studies. II. Relative flavor contributions of individual volatile components. J Dairy Res. 46:523-9. Manning, D.J. and Moore, C. 1979. Headspace analysis of hard cheeses. J Dairy Res 46:539-45. Marilley, L. and Casey, M.G. 2004. Flavours of cheese products: metabolic pathways, analytical tools and identification of producing strains. International Journal of Food Microbiology. 90:139– 159.


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McSweeney, P.L.H., Nursten, H.E. and Urbach, G.1997. Flavours and off-flavours in milk and dairy products. In: Fox, P.F. (Ed.), Advanced Dairy Chemistry, vol. 3. Chapman & Hall, London, pp. 403–468. 2nd ed. McSweeney, P.L.H. and Fox, P. F.1997. Indices of Cheddar cheese ripening, Proc. 5th Cheese Symp., Moorepark, Fermoy, Co. Cork, Ireland, pp 73–89. Melchiorsen, C.R., Jokumsen, K.V., Villadsen, J., Israelsen, H. and Arnau, J. 2002. The level of pyruvate– formate lyase controls the shift from homolactic to mixed-acid product formation in Lactococcus lactis. Appl. Microbiol. Biotechnol. 58:338– 344. Milo, C. and Reineccius, G.A. 1997. Identification and quantification of potent odorants in regular-fat and low-fat mild Cheddar cheese. J Agric Food Chem 45:3590-4. Mulder, H. 1952. Taste and flavor-forming substances in cheese. Neth Milk Dairy J 6:157-67. Ney, K.H. and Wirotma, I.P.G. 1978. Investigation of aroma constituents of Fontina, an Italian cheese. Fette Seifen Anstrichmittel 80:249-51. Cited from Urbach G (1997b). Ney, K.H. 1981. Recent advances in cheese flavor research. In: Charalambous G, Iglett G, editors. The quality of foods and beverages. Vol. 1. Chemistry and technology. New York, N.Y. Academic Press. pp 389-435. Olson, N.F.1990. The impact of lactic acid bacteria on cheese flavor, FEMS Microbiol. Rev. 87: 131–147. Price, J.C. and Manning, D.J. 1983. A new technique for the headspace analysis of hard cheese. J Dairy Res 50:381-5. Puchades, R., Lemieux L. and Simard R.E. 1989. Evolution of free amino acids during ripening of Cheddar cheese containing added lactobacilli strains, J. Food Sci. 54: 885–888, 946. Rijnen, L., Bonneau, S. and Yvon, M. 1999a. Genetic characterization of the lactococcal aromatic aminotransferase and its involvement in conversion of amino acids to aroma compounds. Appl Environ Microbiol 65:4873-80. Rijnen, L., Delacroix-Buchet, A., Demaizieres, D., Le Quere, J.L., Gripon, J.C. and Yvon, M. 1999b. Inactivation of lactococcal aromatic aminotransferase prevents the formation of floral aroma compounds from aromatic amino acids in semihard cheese. Intl Dairy J 9:877-85. Rychlik, M., Warmke, R. and Grosch, W.1997. Ripening of Emmental cheese wrapped in foil with and without addition of Lactobacillus casei subp. casei. III. Analysis of characteristic impact flavour compounds, Lebensm. Wiss. u. Technol. 30:471-478.


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Singh, T.K., Drake, M.A. and Cadwallader, K.R. 2003. Flavor of Cheddar Cheese: A Chemical and Sensory Perspective. Comprehensive Reviews in Food Science and Food Safety. 2:139- 162 Syu, M.J. 2001. Biological production of 2, 3-butanediol. Appl. Microbiol. Biotechnol. 55:10– 18. Thomas, T.D. and Pritchard, G.G. 1987. Proteolytic enzymes of dairy starter cultures. FEMS Microbiol Rev 46:245-68. Urbach, G. 1995. Contribution of lactic acid bacteria to flavor compound formation in dairy products. Intl Dairy J 5:877-903. Visser, S. 1993. Proteolytic enzymes and their relation to cheese ripening and flavor: an overview. J Dairy Sci 76:329-50. Weimer, B.C., Seefeldt, K. and Dias, B. 1999. Sulfur metabolism in bacteria associated with cheese. Antonie van Leeuwenhoek 76:247-61. Wijesundera, C., Drury, L., Muthuku-marappan, K., Gunasekaran, S. and Everett, D.W. 1998. Flavour developmenet and distribution of fat globule size and shape in Cheddar–type cheeses made from skim milk homogenised with AMF or its fractions, Aust. J. Dairy Technol. 53:107. Wong, N.P., Ellis, R., La Croix, D.E. and Alford, J.A. 1973. Lactones in Cheddar cheese. J Dairy Sci 56:636.


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ANALYTICAL TECHNIQUES FOR CHARACTERIZATION OF FLAVOURING COMPOUNDS IN DAIRY PRODUCTS

Dr. Rajesh Kumar, Dr. R.B. Sangwan and Dr. Bimlesh Mann Dairy Chemistry Division NDRI, Karnal Introduction: It is not uncommon for volatile and semi volatile organic molecules in ppb (parts per billion) or ppt (parts per trillion) concentration to cause off-flavours (OF). Today, sophisticated and sensitive analytical tests are capable of detecting, identifying and quantitating the specific chemical agents responsible for off-flavours. Once specific causes for off-flavours have been identified, dairy scientists can usually delineate their mechanism of formation (e.g., microbial spoilage, overheating, oxidation, photodegradation, sanitizer contamination, etc.) and take steps to reduce off-flavours. Furthermore, new analytical techniques are so powerful that they can often accomplish this with speed, accuracy and reliability which is not possible using sensory analysis alone. Combining the benefits of modern analytical testing, particularly gas chromatography with mass spectrometry detection (GC-MS), with sensory analysis results in a powerful tool for off- flavours elucidation. Instrumental analysis GC is a form of partition chromatography in which the separation takes place between the stationary phase (a film coated on a solid support) and the mobile phase (a carrier gas) flowing over the surface of the film in a controlled fashion. Because of their superior separation efficiency and versatility, GC methods are the most commonly used analytical techniques in flavor research. GC has tremendous separating power, sometimes in excess of 200,000 theoretical plates per column. This attribute is essential for the separation of complex flavour isolates. Using mass spectrometry as the detector for GC analysis, allows for identification of chromatographic peaks that elute from the column. Mass spectrometry (MS) is a form of spectroscopy in which the molecule is exposed to high-energy electrons and through a sequence of steps is broken down into unique charged molecular fragments. The uniqueness of this process allows the method to be used for identification/confirmation of an unknown compound with a sensitivity of 10-100pg. MS is generally used in the flavour area either to determine the identity of an unknown or to act as a mass selective GC detector. GC-MS is an analytical technique used to identify/ confirm the identity of compounds as they elute from the GC column and has proven to be one of the most useful analytical techniques for studying volatile and semi volatile odour active chemicals in dairy products. The volatile and semi volatile compounds, in the headspace, are of interest


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because they can travel to the nose during eating and stimulate the olfactometry receptors in the nasal cavity. Mass spectrophotometers may be classed as low resolution (LR) or high resolution (HR) instruments. The LR instruments provide mass measurements to the closest whole mass unit, but do not provide elemental composition. High resolution instruments provide sufficiently accurate mass measurements to permit determination of elemental composition. In addition to MS detectors, flavor chemists sometimes employ extremely sensitive detectors for specific classes of compounds. One example is the pulsedflame photometric detector (PFPD) for sub-ppb measurement of organic sulfur compounds, chemicals that often have extremely low odour threshold detection levels. The determination of the chemical(s) responsible for an off-flavour in a sample usually involves three steps: preparing the sample for analysis, injecting the sample (or usually an extract of the sample) into the GC-MS and data processing. In addition, many analytical systems are now used by flavor chemists to incorporate an olfactometry detector. With this method, the effluent that elutes from the end of the analytical GC column is split, with a portion of the flow going to the MS detector and a portion going to an olfactometry detector (OD), which is often referred to as a sniff port. While some of the sensitivity of the MS detector is lost, an important advantage is gained: The analyst can sniff each peak as it elutes from the column and determine its odour characteristics. By using GC-MS-OD, the flavor chemist is able to determine the identity, concentration, odour characteristics and odour intensity of each chromatographic peak. Sample Preparation: A Key Step in Chemical Analysis of Dairy Foods It is usually not possible to directly inject a food sample into a GC without performing some sample preparation. Proteins, fats, complex carbohydrates and other nonvolatile chemicals will degrade in the heated GC injector, resulting in the formation of numerous artifact peaks that can degrade column performance and obscure peaks of interest. Separating volatile compounds from matrix interferences and concentrating volatiles (which can be present in concentrations as low as 10-8 to 10-14%), so that they can be detected, usually requires sample preparation involving volatile isolation and concentration steps. Unfortunately, there is no single perfect sample preparation technique for flavor research. The aroma volatiles in food samples can be heterogeneous, covering a wide range of polarities, solubilities, functional groups, vapor pressures, concentrations and volatilities. Other complications include instability of aroma volatiles to certain conditions (oxygen, light, heat, pH, etc.) and the possibility that aroma volatiles may interact with chemicals in the food matrix. It is important that the extraction technique does not introduce or create volatiles that are not in the dairy product being tested. For example, sample preparation techniques that involve heating the sample to high temperatures (e.g., steam distillation) can generate artifact peaks in sample chromatograms, and these odoriferous artifacts may


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be misinterpreted as the cause of the OF problem in the product. In some cases, more than one procedure may be required for optimum recovery of flavor compounds. Dairy chemists now have a wide variety of sample preparation techniques that they can use for isolating and concentrating odour-active chemicals prior to GC analysis. Frequently used sample preparation methods for flavor analysis include vacuum distillation, simultaneous steam distillation/extraction (also referred to as the Liken and Nickerson extraction procedure), static headspace, dynamic headspace and solidphase microextraction (SPME). Some of the more popular sample preparation techniques for flavor analysis are discussed below. (a) Solvent extraction and distillation: Solvent extraction commonly involves the use of pentane, dichloromethane, diethyl ether or some other volatile organic solvent. This limits the method to the isolation of fat-free foods unless an additional procedure is employed to separate the extracted fat. W. Engel et al. (1999) developed a new distillation unit, called solvent assisted flavor evaporation (SAFE), for the extraction of flavor volatiles from complex aqueous matrices, such as beer, fruit juices, milk and cheese. The distillation vessel and “transfer tubes” are thermostated at low temperatures (20°-30°C) to avoid condensation of compounds with high boiling points, and the sample is added by dropping aliquots from the funnel into the vessel to reduce time of extraction. This new method allows for the use of solvents other than diethyl ether and dichloromethane, and it could be used for extracts containing large concentrations of fat. Another advantage of the SAFE technique is that recovery of really authentic flavor—i.e., a flavor sample with organoleptic properties as close as possible to the natural product—is possible. Solvent extraction methods have disadvantages. Large volumes of solvent must be evaporated while retaining the volatile flavor components. Another problem is that sample preparation is time consuming; only one or two samples can be extracted per day. (b) Headspace techniques: Static headspace: If a complex material, such as milk, yoghurt or cheese, is placed in a sealed vessel, some of the more volatile compounds in the sample matrix will leave the sample and pass into the headspace around it. If the concentration of the volatile compound reaches about 1 ppm in the headspace, it may be assayed by a simple injection of an aliquot in the vessel. How much compound enters the headspace depends on several factors, including its concentration in the original sample, the volatility of the chemical, the solubility of the chemical in the sample matrix, the temperature of the vessel and how long the sample has been inside the vessel. In practice, the food sample is placed into a headspace vial, sealed and warmed to enhance vaporization of the volatiles and incubated for a period of time to establish equilibrium at the incubation temperature. Once the volatiles have equilibrated, an


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aliquot of the headspace gases is withdrawn with a syringe and injected into the GC. As an alternative, the equilibrated headspace may also be allowed to pass through a sample loop of known volume, which is subsequently flushed into the injection port. Static headspace methods eliminate the large solvent peak, which may obscure important odour-active analytes. Static headspace is a relatively rapid technique that is easily automated, making it attractive for sample screening applications. The combination of careful monitoring of temperature and equilibrium time, pressure control of the sample loop and automatic injection provides increased reproducibility over manual attempts at headspace analysis and reduces labour costs. Additional advantages include low cost per analysis, simple sample preparation and the elimination of reagents. Relatively poor sensitivity compared to other types of sample preparation techniques is a disadvantage of static headspace method. The maximum temperature for most food products is less than the boiling point of water. Analysis at this fairly low temperature limits the usefulness of the technique for analytes with boiling points over approximately 130°C. Many materials that may be extracted with solvents may elute well at higher GC column temperatures but will be poorly represented in a static headspace chromatogram. Also, reproducibility depends on analyzing a sample after it has reached equilibration, and the time required to achieve this point may, especially for less volatile compounds, be a drawback for some analyses. Dynamic headspace: With dynamic headspace techniques, the food sample, which is normally heated to 40° - 60°C, is purged with helium gas. Instead of allowing the sample volatiles to come to equilibrium, the atmosphere around the sample material is constantly swept away by a flow of carrier gas, taking the volatile analytes with it. The volatiles that are swept away are directed to a trap (commonly Tenax), where they are collected and stored until the end of the purging cycle is reached and the trap is ready to be desorbed onto the GC column. By removing the volatiles in a continuous fashion, more molecules of the volatiles in the sample are collected for analysis, greatly improving the sensitivity of the test. (Note: In general, the term “purge-and-trap” is used to refer to liquid samples analyzed by bubbling the carrier gas through the liquid, while “dynamic headspace” is used when the sample material is a solid.) Dynamic headspace is significantly more sensitive than static headspace. Compared to solvent extraction techniques, it offers the advantages of no solvent to evaporate, no interfering solvent peaks in chromatograms and relatively simple automated sample preparation. The disadvantages include more complicated instrumentation. Instrumentation must monitor several steps, valving, heated zones, etc. Instrumentation is more expensive than static headspace instrumentation. Because of complex functioning of the instrument, there are many opportunities for malfunction, including heater damage, valve leaking, contamination and cold spots. Compared to static headspace, dynamic headspace techniques require a little more


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time per sample (for purging, trap drying and trap transfer, all of which typically require approximately 15 min). However, the technique is much faster than most solvent extraction techniques. (c) Solid-phase microextraction (SPME): SPME uses a short, thin, solid rod of fused silica (typically 1 cm in length with an outer diameter of 0.11 mm) coated with an absorbent/adsorbent polymer. The coated fused silica (the SPME fiber) is attached to a metal rod, and both are protected by a metal sheath that covers the fiber when it is not in use. The assembly is placed in a fiber holder. The system is a modified syringe. Two sampling methods can be used with SPME depending on the placement of the fiber relative to the sample— immersion or headspace sampling. For dairy products, which contain high levels of fat, carbohydrate and protein, the headspace technique is preferred. In SPME headspace analysis, a fiber is placed in the headspace above the sample. For example, when analyzing volatiles in a milk sample, 3 mL of milk can be placed in a 9 mL glass GC vial containing a small stirring bar and sealed with a septum closure. The sample is then heated (e.g., to 50°C). The fiber is then exposed to the headspace gases for 10 - 30 min, depending on the sample matrix and the analytes of interest. After sample exposure time has elapsed, the fiber is retracted into the needle assembly and removed. The extracted volatiles are thermally desorbed from the fiber in the heated GC injector and transferred to the GC column for separation and analysis. Several types of fibers with varying affinities for specific classes of compounds are available. SPME is particularly well-suited to the analysis of dairy products. The technique is capable of extracting a broader range of analytes than is possible with other headspace techniques. For example, SPME is capable of ppb detection levels for both low molecular weight, highly volatile compounds like acetaldehyde, dimethyl sulfide, acetone and 1,3-pentadiene, as well as high molecular weight, high-boilingpoint compounds like vanillin, lactones and dodecyl aldehyde. Furthermore, it can be used for quantitating free fatty acids (C4 through C14) in dairy products. This important class of flavor compounds can be particularly challenging and time consuming to extract by other techniques. Incorporating the nose in chemical analysis: The application of new and improved volatile extraction techniques prior to GC-MS in conjunction with modern, sensitive bench top GC-MS instruments often results in dairy sample chromatograms with 100 or more peaks. Unfortunately, the relevance of each peak to a sample’s flavour or OF is not easy to evaluate. One of the major problems in aroma research is to select those compounds that significantly contribute to the aroma of a food. In general, the aroma of a food consists of many volatile compounds, only a few of which are relevant to odour and flavour. A first essential step in aroma analysis is the distinction of the more potent odorants from volatiles having low or no aroma activity. GC in combination with olfactometric techniques (GC-O) is a valuable method for the selection of aroma-active components Sensory and Related Techniques for Evaluation of Dairy Foods

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from a complex mixture. GC-O is a way for flavor chemists to incorporate the sense of smell into their chemical analysis. GC-O is now accepted as one of the most powerful ways to give sensory meaning to the long lists of volatiles appearing in sample chromatograms. GC-O consists of experiments based on human subjects sniffing GC effluents. Experience shows that many key aroma compounds occur at very low concentrations; their sensory relevance is due to low odor thresholds. Thus, the peak profile obtained by GC does not necessarily reflect the aroma profile of the food—that is, sometimes the largest chromatographic peaks in a food extract have the least amount of aroma impact on the food, while the smallest peaks may have the most significant impact. In general, it is very difficult to judge the sensory relevance of volatiles from a single GC-O run. Several techniques are in use to help with this problem. This is based on successive dilutions and GC-injection of a flavor extract, until the assessor no longer detects the odour at the sniffing port. For each GC-elution, the assessor presses a button during the perception of odours to generate individual olfactograms (or aromagrams) made of a series of square signals. After data treatment, a computergenerated global olfactogram assigns greater importance to odour peaks that are smelled in the highest dilution of the extract. Conclusion: The advent of new, sensitive and rapid analytical methods in conjunction with olfactometry techniques and traditional sensory taste paneling approaches have greatly improved the understanding of flavour-impact chemicals in dairy products. By working together, sensory scientists and analytical flavour chemists can help the dairy industry to determine and correct the causes of off-flavours in dairy foods. This will assist in reducing waste and customer complaints and help processors develop ways to increase shelf-life of dairy products. References: Chaintreau, A. Quantitative Use of Gas Chromatography- Olfactometry: The GC“SNIF” Method. In Flavor, Fragrance and Odor Analysis, Marsili, R.T. (ed.), New York: Marcel Dekker. pp. 333-348 (2002). Engel, W., Bahr, W. and Schieberle, P. Solvent-assisted flavor evaporation—a new and versatile technique for the careful and direct isolation of aroma compounds from complex food matrices. Eur. Res. Technol. 1999; 209:237-241. Marsili, R.T. Comparison of solid-phase microextraction and dynamic headspace methods for GC-MS analysis of light-induced lipid oxidation products in milk, J. of Chrom. Sci. 1999; 37:17-23. Marsili, R.T. Flavours and off-flavours in dairy foods. In Encyclopedia of Dairy Sciences, Roginski, H., Fuquay, J.W. and Fox, P.F. (eds.),London: Academic Press. pp. 1069-1081 (2003).


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Werkhoff, P., Brennecke, S., Bretschneider, W. and Bertram, H.J. Modern methods for isolating and quantifying volatile flavor and fragrance compounds. In Flavor, Fragrance and Odor Analysis, Marsili, R.T. (ed.), New York: Marcel Dekker. pp. 139-204 (2002).


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SENSORY ATTRIBUTES OF MILK PROTEINS

Dr. Vijay Kumar Gupta Principal Scientist Dairy Technology Division N.D.R.I., Karnal-132 001 1.

INTRODUCTION

Edible casein, caseinates as salts of sodium, calcium, potassium, magnesium etc., whey protein concentrates (30-80% protein), coprecipitates and protein hydrolysates are the major milk protein products. They are used in bakery products, meat products, confectionery items, beverages and in a wide variety of formulated foods and animal feed products. They are also increasingly being used in dietary preparations and pharmaceutical and medical applications. Most of the applications of milk protein products require them to be neutral or bland in taste and smell, colourless and free from extraneous matter. However, a lot more attention has been given on the flavour aspects of these products in the literature than on appearance, as flavour is considered the most important sensory quality. 2.

STANDARDS FOR SENSORY ATTRIBUTES OF MILK PROTEIN PRODUCTS

Among the different protein products, only edible casein has been assigned national and international standards, particularly with respect to sensory qualities. As per BIS standards (IS:1167-1965), casein shall be nearly white or pale cream in colour and shall have no undesirable odour or any foreign matter; it shall be free from any added colour. The size of the particles shall be such that 100% by weight of casein shall pass through 500-micron IS sieve. As per international standards (FIL - IDF 45:1969), flavour and odour of acid precipitated edible casein must be neutral, free from offensive flavours, taste and odours such as sour, cheese or metallic off-flavours. Colour of the product should be white to pale cream. If ground, it should be free from lumps that do not break up under slight pressure. The maximum sediment (scorched particles) allowed is 22.5 mg in 25 g spray dried and 32.5 mg in 10 g roller dried product. The casein should not contain any foreign matter such as particles of wood, metal, hairs or fragments of insects. European Community standards (No. L237/29) are more or less similar to international standards in respect of sensory attributes. 3.

FLAVOUR OF MILK PROTEIN PRODUCTS

Freedom from flavour defects is very important in many of the applications of milk proteins as food ingredients. In industrial practice, fresh casein, caseinates, coprecipitates and whey proteins are usually bland in flavour. On storage, milk proteins tend to develop unpleasant flavours variously described as gluey, stale, burnt-feather or musty. Good progress has been made in research into the origins of


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the flavours. Ramshaw & Dunstone (1969a, b) found a large range of volatile components in the steam distillate of gluey casein. Their findings suggested that the flavour resulted from a mixture of compounds with some synergistic effect from oaminoacetophenone, a compound of low volatility possibly arising from breakdown of tryptophan. The type of compounds which seemed significant in the flavour spectrum and their experiments on manufacture of casein and coprecipitates indicated that non-enzymatic browning reactions were involved in the off flavour development. It appeared that reducing substances produced by this reaction subsequently degraded to flavour components. Ramshaw & Dunstone (1970) reported trials in which dispersions of milk proteins were heated to encourage this degradation so that the volatile flavour components could be removed during spray drying. By using browning inhibitors (1970b), they also obtained improved flavour stability of lowCalcium-precipitate, where the longer heating time for the milk can initiate browning reactions. Industry has sought to obtain the best flavoured product by such techniques as reducing the lactose content by thorough washing and avoiding excessive heating at any stage of manufacture so as to minimise browning reactions. The manufacture of caseinate from fresh wet curd and minimizing its storage time before use also helps in obtaining the best flavour. However, On the basis of comparing ferricyanide reducing values with flavour of low lactose casein, Walker (1970) concluded that the browning reaction did not contribute significantly to development of musty off-flavour. Sharma & Hansen (1970) linked development of gluey flavour on heating casein with breaking of ester phosphate bonds. Ramshaw & Leary (1970) found that UV treatment of casein gave unpleasant odours as well as gluey flavour. The treatment appeared to accelerate degradation of tryptophan but not the browning reaction. Table 1 gives the threshold concentration of gluey flavour in treated and untreated casein. Table 1. Threshold concentration of gluey flavour in treated and untreated casein ___________________________________________________________________ Materials and/or treatment Threshold Remarks (%) concentration ___________________________________________________________________ Gluey casein 0.3 Control Gluey sodium caseinate 0.3 Control Fresh freeze-dried casein or sodium caseinate >3.0 Control Vacuum-treated casein or caseinate 0.3 Flavour not removed Steam-distilled sodium caseinate >1.0 Distillate gluey Freeze-dried sodium caseinate (1, 5, 10%) 0.3 Flavour not removed Reprecipitated casein removed 1.0 Flavour partially Filtrate from reprecipitation 1.0 Filtrate gluey Washed casein r emoved >1.0 Flavour partially Wash water 1.0 Wash water gluey Activated carbon-treated casein >3.0 Flavour removed Sephadex G 25-treated casein >3.0 Flavour removed _______________________________________________________________________________ *Concentration at which gluey flavour was first detectable


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The flavour of coprecipitates tends to follow a similar pattern to that of the caseins, high calcium coprecipitates being more stable than low calcium (acid) coprecipitates and fresh-curd soluble coprecipitates being better than those reconstituted from dry, granular, insoluble coprecipitates (Southward and Goldman, 1978) The coprecipitates, as a class, may also tend to exhibit 'cooked flavour' overtones as a result of the high heat treatment given to the milk during their manufacture (Southward, 1985). Particle size of granular caseins and coprecipitates also appears to affect their flavour; finely ground product tend to exhibit stronger off-flavours than coarser fractions. Whey protein concentrates develop a typically stale off-flavour during storage due to a set of complex, inter-related chemical reactions which include lipid oxidation and Maillard browning. There is no information in the literature on the volatile organic compounds responsible for off-flavour in whey protein concentrates (Morr and Ha, 1991). Important possible off-flavours in milk protein products are listed in Fig. 1. 4.

METHODOLOGY FOR THE EVALUATION OF THE FLAVOUR OF MILK PROTEIN PRODUCTS

A method was developed at New Zealand Dairy Research Institute that has been widely used to assess the flavour characteristics of protein products. Sodium or calcium caseinate is dissolved in water at 60°C, using mechanical stirring, to produce 10% (w/v) caseinate solutions. Acid casein is treated similarly except that sodium hydroxide solution is carefully added to dissolve the casein to produce solutions of sodium caseinate at pH 6.7. Rennet casein is dissolved with sodium tripolyphosphate (5% w/w of casein) to produce solutions of pH 7-8. Because the viscosity of a rennet casein solution is greater than that of a sodium caseinate solution, the concentration of the rennet casein is usually reduced to 8% (2/v) but, for calcium caseinate, which is less viscous than sodium caseinate, the concentration is not increased correspondingly. The coded samples to be tasted (all of one type, such as acid casein, or sodium caseinates, etc.) are presented in random order to each taster at a temperature of about 40°C. Marked and coded 'good' and 'bad' control samples are included. Water and dry bread are used between each sample to remove dry lingering impression from the mouth. A typical flavour evaluation score sheet, as used for all casein products, is shown in Fig. 1. To assist the taster in describing off-flavours, the score sheet includes a list of suggested serius and non-serius off flavour descriptions. The taster is asked to give an overall score (scale 0-8, where 8 = excellent, 6 = good, 3 = poor, 0 = extremely objectionable) to each sample based on the type and intensity of offflavour. A guide for relating the type and intensity of off-flavour to the overall score is also given ; serious off-flavours absent, 8; threshold, 7; slight, 5 etc. Mean values and


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FLAVOUR EVALUATION OF MILK PROTEIN PRODUCTS Evaluator_______________ Product__________________

Date_________________

Desirable Flavour : Bland Flavour Suggested off-flavours : Serious

Non-serious

Astringent Bitter Puckery Burnt (cooked) Card board Fishy Metallic Mouldy Gluey

(Ast) (Bit) (Puc) (But) (Cbd) (Fsh) (Met) (Mol) (Glu)

Acidic Caramel Cereal Milky Nutty Sweet

Putrid

(Put)

Rancid Salty Soapy Stale Storage Whey

(Ran) (Sal) (Spy) (St) (Sto) (Wh.)

(Ac) (Car) (Cer) (Mlk) (Nut) (Swt) Guide for overall Score (8-0)

Off Flavour Serious offintensity flavour Absent (Abs) 8 Threshold (Thr) 7 Slight (Sl) 5 Moderate (Mod) 3 Strong (Str) 1

Non-serious offflavour 8 7 6 5 3

Note:- Type of off flavour may be described by using abbreviated terms Sample No. 1 2 3 4 5

Serious off-flavour Off Flavour

Intensity

Non-serious off-flavour

Over all Score

Off Flavour

Time of Evaluation_____________AM/PM Evaluator

Intensity

Signature of the

Fig. 1. Score-card for flavour evaluation of milk protein products


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standard deviations for overall score and intensity of off-flavour are computed in the usual way. For the purpose of summarizing the information, off flavour intensity is converted into a score: 1 = absent, 2 = threshold, 3 = slight, 4 = moderate, 5 = strong. The use of a large panel of trained tasters and the inclusion of reference points for both ends of the scoring range (control samples) provide a reasonably reliable estimation of the flavour quality of any casein sample. Mean panel scores at the bottom (0-3) and top (6-8) of the range are normally more reliable than those in the middle (4-5) where standard deviations of greater that 1 are not uncommon. In general, however, the method has been a valuable tool for placing casein products into various flavour categories prior to selecting them for use in foods. 5. APPEARANCE OF MILK-PROTEIN PRODUCTS Granular casein should be of uniform particle size prescribed in standards, or of commercially desired mesh sizes like 30, 60 and 90. Desirable colour of casein is white to pale cream; however, buffalo milk casein has natural greenish tinge. Browning and other discolourations are the colour defects. Caseinates, whey protein concentrates and coprecipitate powders should possess almost similar colour as the casein. Whey protein concentrates, coprecipitates and sodium, potassium and ammonium caseinates make translucent, viscous, strawcoloured solutions, while calcium caseinate forms micelles in water, producing an intensely white, opaque, 'milky' solution of relatively low viscosity. 6. PROTEIN HYDROLYSATES The production of protein hydrolysates provides an opportunity for the dietary management of persons suffering from digestive disorders as a result of pancreatic malfunction, pre-and post operative abdominal surgical patients, patient on geriatric and convalescent feeding, and others who for various reasons are not able to ingest a normal diet. However, enzymatic hydrolysis of protein has frequently been shown to give bitter taste to digests due to liberation of bitter tasting peptides or amino acids. In aqueous solution, hydrophilic or polar groups of casein are on the outer surface and hydrophobic groups are packed inside the molecule. Enzymatic digestion exposes the peptide moieties which contain large amount of hydrophobic amino acids which on contact with the taste buds give a sensation of bitterness. Khanna (1991) used a 9-point Hedonic scale for comparison of sensory quality of casein hydrolysates adjusted to 10% T.S. concentration. For sensory evaluation of bitterness of casein hydrolysates, Khanna (1991) used 4- point scale, where 1 = extremely bitter, 2 = distinctly bitter, 3 = slightly bitter, and 4 = not bitter. Saline water (2%) was provided to the judges for rinsing their mouth before tasting each sample. The judges noticed the following sensory characteristics in different samples of casein hydrolysates: i) Flavour : Stale, foul, acidic, salty, sour and fruity.


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ii) Colour : Dull white, yellowish, sparkling clear, yellowish brown and red. iii) Sediment : No sediment. REFERENCES Kelly, P.M. (1986) Dried milk protein products. J. Soc. Dairy Technol., 39 (3): 81-85. Khanna, R.H. (1991) Process optimization for enzymatic production of casein hydrolysate. M.Sc. Thesis, NDRI deemed University, Karnal. Muller, L.L. (1971) Manufacture and uses of casein and coprecipitates, Dairy Sci. Abstr., 33: 659. Morr, C.V. and Ha, E.Y.W. (1991) Off flavours of whey protein concentrates : A Literature Review. Int. Dairy J., 1: 1-11. Ramshaw, E.H. and Dunstone, E.A. (1969a) The flavour of milk protein. J. Dairy Res., 36, 203-213. Ramshaw, E.H. And Dunstone, E.A. (1969b) Volatile compounds associated with the off-flavour in stored casein. J. Dairy Res., 36: 215-223. Ramshaw, E.H. and Dunstone, E.A. (1970a) Ferricyanide reducing substances and the flavour of milk protein heated in solution. XVIII Int. Dairy Cong., IE: 424. Ramshaw, E.H. and Dunstone, E.A. (1970b) Inhibition of browning during milk protein manufacture and storage. XVIII Int. Dairy Cong., IE: 425. Ramshaw, E.H. and Leary, J. (1970) Volatile components in casein after exposure to UV light. XVIII Int. Dairy Congr., IE: 64. Sharma, K.K. and Hansen, P.M.T. (1970) Heat-induced dephosphorization of dehydrated caseins. XVIII Int. Dairy Cong., IE: 58. Roeper, J., Southward, C.R. and Humphries (1978) A method for the evaluation of the flavour of casein products. N.Z. J. Dairy Sci. Technol., 13: 124-126. Southward, C.R. (1985) Manufacture and applications of edible casein products. 1. Manufacture and properties. N.Z. J. Dairy Sci. Technol., 20: 70-101. Southward, C.R. and Goldman, A. (1978) Coprecipitates and their application in food products. II. Some properties and applications. N.Z. J. Dairy Sci. Technol., 13: 97105. Walker, N.J. and Manning D.J. (1976) Components of the Musty off-flavour of stored dried lactic casein. N.Z.J. Dairy Sci. Technol. 11, 1. Walker, N.J. (1970) Chemical changes involved in the development of off-flavour in stored casein. XVIII Int. Dairy Cong., IE: 426. Walker N.J. (1973) Flavour defects in edible casein and skim milk powder, II The role of aliphatic monocarbonyl compounds. J. Dairy


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SENSORY EVALUATION OF DRIED MILK AND MILK PRODUCTS

Dr. Vijay Kumar Gupta Principal Scientist Dairy Technology Division N.D.R.I., Karnal - 132 001 1.

INTRODUCTION

Milk powders possess various organoleptic, physico-chemical and reconstitutional properties, which are important to both industrial and consumer use. These properties are the basic elements of quality specifications for milk powders. During drying process, care is taken to conserve as much as possible the natural properties of the original raw milk. Quality of dried products should be such that when reconstituted with water, give little or no evidence of detrimental change compared to the original liquid products. Evaluation of milk powder, whole or skimmed, on the basis of its sensory characteristics plays an important role towards its consumer acceptance. 2.

DRY WHOLE MILK

In judging whole milk powder (WMP) for flavour one first classifies the product for flavour as good, fair or poor. 2.1

Off Flavour

Milk powders are expected to demonstrate a slightly sweet, clean and pleasant flavour, though other dried milk products may be expected to confirm to certain other specific requirements. Often, dry milk gradually loses its sweet, fine, appetizing flavour upon aging, thus becoming more or less off flavoured. The more frequently occuring flavour defects of dry whole milk are discussed below: 2.1.1 Oxidized/tallowy: Dry whole milk and other dry high-fat milk products undergo oxidative deterioration (also called tallowy). Whole milk powder with low to medium preheat treatments (equivalent to a WPNI of about 3-5) has a greater tendency to undergo lipid oxidation, with distinctive tallowy and musty flavours, than powders made with higher heat treatments. Chemical changes result with the addition of oxygen to the double bonds of unsaturated glycerides, giving at first peroxides and later aldehydes, ketones etc., which impart the unpleasant flavour. Copper and iron act as catalysts. Higher storage temperature, higher acidity, sunlight and ultra violet irradiation promote faster development of oxidative deterioration. 2.1.2 Rancid: Rancidity is due to hydrolysis of fat through lipase enzyme leading to Sensory and Related Techniques for Evaluation of Dairy Foods

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production of free fatty acids, like butyric acid. Rancid dry whole milk has a bitter, soapy, unclean taste which is persistent after the sample has been expectorated. TABLE- I Evaluation Card for Milk Powder Name........................................................... Code No...................

Dated........................ Time.........................

A. Score the sample for different characteristics. Indicate the degree of defects, if any, encircling the applicable one and deduct accordingly from the attribute score. Characteristic

Max Score

(1)

(2)

Minimum for each attribute (3)

Sample Score (4)

i) Package Appearance

5

3

ii) Appearance of Dry Product

15

9

iii) Appearance of reconstituted milk

15

9

iv) Body and texture of reconstituted milk

20

17

v) Flavour of reconstituted milk

45

27

Note : If the sample score is less than the minimum for any characteristic, it is to be rejected. B. Degree of Defects CHARACTERISTICS (1) i) Appearance of package ii) Appearance of dry product iii) Appearance of reconstituted milk

DEFECT

DEGREE OF DEFECT Suspicion

Definite

(3)

(4)

(5)

Soiled surface unsealed

1

2

3

Caked/ brown particles

2

5

10

Lumpy brown

1

2

5

(2)


Pronounced

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iv) Flavour

Oxidized/stale/ rancid

2

3

10

Chalky/acid/neutralizer/ salty Metalic/cooked/scorched

2

5

10

1

2

5

Weedy/bitter/ foreign

5

10

15

Source: Method for Sensory Evaluation of Milk Powder. Indian Standard. IS : 100301981 2.1.3 Stale, storage, old: Stale flavours, due to carbonyl compounds, can be detected in milk powders almost as soon as they are made. The mechanism of formation of these compounds may be through the Maillard reaction, but many compounds contribute to a stale, cardboard flavour, including oxidation by products. The defect is accelerated by high moisture content and high temperature of storage. When the defect is intense it may be accompanied by a darkening of the product. 2.1.4

Cooked flavour

Milk powders often have cooked flavour, which results from components formed during preheating and possibly during evaporation. During drying, conditions are mostly not such that off-flavours are induced. On the contrary, a considerable part of the volatile sulphydryl compounds (especially H2S) is removed. A cooked flavour in milk powder mainly results from methyl ketones and lactones formed by heating of the fat (they thus are almost absent in skim milk powder) and form Maillard products. . 2.2

Physical characteristics of WMP

Two defects pertaining to the body and texture of dry whole milk are lumpy and caked. 2.2.1 Lumpy: A lumpy powder definitely lacks homogeneity. Hard lumps ranging in size from a grain of wheat upwards may be interspersed throughout. This defect is found more frequently in the spray process product. Lumps result from insufficient drying, drippage from spray nozzles or exposure to moisture laden air. 2.2.2 Caked: Usually this defect is not encountered in dry whole milk. When it does occur, the product loses its powdery consistency and becomes a rock like solid. When the solid mass is broken up, it remains in chunks, thus failing to return to the original powder state. This defect is serious since such milk solids have lost their sales value for human consumption.


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2.3

Discolouration

Milk powder should be uniform in colour, free from foreign specks and burnt particles. It should exhibit greenish white or creamish white colour, respectively in buffalo and cow milk powders. Milk powder tends to darken during storage, turning to brown due to maillard reaction, which refers to the reaction between free amino group of protein and lactose. This is associated with old or stale off-flavour. High moisture content and high storage temperature enhance browning discolouration. Spray dried milk powder is more susceptible to age darkening and to greater intensity than roller process powders. 2.3.1 Browned or darkened: The defect is usually associated with an old, stale flavour. The normal creamy colour is replaced by a distinct brown. 2.3.2 Scorched: Discolouration due to burning of the milk solids is usually associated with the roller process. The powder may vary from light to dark brown. 2.3.3 Lack of uniformity: This defect may be due to either partial discolouration (browning) after packaging or to partial scorching during the manufacturing process.

3.

SKIM MILK POWDER (SMP)

3.1

Flavour

Due to its low fat content, SMP does not possess the rich flavour of high fat milk powder. The flavour of high quality non fat dry milk should be clean, sweet and pleasant, when reconstituted, similar to that of fresh skim milk. The flavour may have a slightly cooked or heated note. The chief flavour defects of non fat dry milk are as follows: 3.1.1 Stale, storage, old: This flavour defect is the chief one of non fat dry milk. In this product the off-flavour is even more "quick" and distinct than in dry whole milk. Usually the flavour defect is accompanied by a darkening of the powder. The old, stale flavour develops usually more intensely in spray process than in roller process powder. 3.1.2 Cooked: As in dry whole milk, this flavour is produced in products which have been subjected to abnormally high heat during processing. 3.1.3 Oxidized, tallowy: Non fat dry milk contains a small percentage of fat which oxidizes under some conditions yielding the oxidized or tallowy flavour. A tallowy


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product has a pronounced odour, whereas stale powder does not have a very intense odour. 3.2

Physical characteristics

Non fat dry milk prepared by spray process is very fine in particle size and uniform throughout. Instead of being flour like in texture, instant SMP is more or less granular. The product pours readily somewhat like that of corn meal. The highly hygroscopic, light, almost air-borne dust of normal spray process is lacking in SMP. 3.3

Discolouration

Non fat dry milk should be uniform in colour throughout showing the absence of foreign specks and burnt solids. The product should have a creamy white or light yellow colour which varies slightly in intensity with the season of the year. Upon ageing under certain conditions SMP tends to darken. When this defect occurs the light yellow colour has given way to a definite brown. Spray process powder appear to be more susceptible to age darkening and to a greater intensity than roller-process powder.

4.

METHOD OF RECONSTITUTING DRY MILK FOR FLAVOUR EXAMINATION

Generally for examining dry milk for odour and taste, the product is reconstituted on the basis of the original concentration. The American Dry Milk Institute (ADMI) recommends examination of dry milk odour immediately after the containers are opened and again for flavour approximately one hour after the sample has been reconstituted. Judges must be mindful of the fact that freshly prepared fluid milk made from water and dry whole milk often possesses a slightly chalky, watery or slightly cooked taste. Hence permitting a short storage period for blending of flavours after reconstituting the product should aid the judge in determining more accurately the true flavour. 5.

MALTED MILK

5.1

Flavour Malted milk, being composed in large part of maltose and dextrose, has a definitely sweet taste. It should have a distinct flavour of malt. The product should be judged for its lack of malt flavour and for oxidized flavour defect. 5.2

Body and texture


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Malted milk has a coarse and grainy texture unlike the fine texture of spray dried milk. While judging, product must be examined for possible stickiness and formation of cakes because of its affinity for water.

6.

REFERENCES

Bodyfelt, M.S., Tobias, J. and Trout, G.M. (1988). The Sensory Evaluation of Dairy Products. AVI Publishing Co., NY, pp. 384 - 415. Indian Standard. Method for Sensory Evaluation of Milk Powder. IS: 10030 - 1981. Prentice, J.H. (1972). Rheology and Texture of Dairy Products. J. of Texture Studies. 3, 415 - 458.


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APPLICATION OF RHEOLOGY IN QUALITY ASSURANCE IN FOOD PROCESSING

Dr. Dalbir Singh Sogi Reader & Head, Dept. of Food Science & Technology Guru Nanak Dev University, Amritsar Quality assurance generally deals with the defining of quality standards of food products quantitatively and then controlling the entire manufacturing process so that finished product conforms to the established standards. Sensory characterustics of a food product are the most important for the consumer acceptability. Sensory parameters refer to appearance (including colour), flavour (taste, odour and Feel) and texture (Solids)/consistency (Liquids). Senses used for evaluation of food qualiry are as follows • • • • • •

Smell : Olfactory – mucous memberane of the nose; olfactory; epithelium Taste : Gustatory-mucous membranne of toungue, palate and throat Sight : Visual - eyes Hearing : Auditory; Aural-ears Touch : Haptic-tactile nerve in general Cut/crush : Teeth

In this presentation only consistency has been discussed. It is a very important quality attribute in liquid or semisolid foods. Apart from colour and flavour, the consistency of food dictates overall acceptability of the products. The consistency has been defiend in number of terms in sensory evaluation for varous food products. The mouth can be considered as an intricate mechanical system and chemical reactor that can crush, wet, enzymetically degrade, pressurize, heat or cool, pump and sense force and temperature. In addition this “eating machine” has a sophisticated feed back control system. The mouthfeel terms of beverages have been classified in Table 1.

Category

Typical words

Beverages that have this property

Beverages that do not have this property

Viscosityrelated terms

Thin

Water, Iced tea, hot tea

Thick

Milk shake, eggnog, tomato juice Milk, liqueur, hot chocolate

Apricot nectar, milk shake, buttermilk Club soda, champagne, drink made from dry mix -

Feel on soft

Smooth


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tissue surfaces Pulpy Creamy Body-related terms

Heavy Watery Light

Coating of oral cavity

Mouth Coating Clinging

Resistance to tongue movement Afterfeelmouth

Slimy Syrupy

Orange juice, lemonade, pineapple juice Hot chocolate, eggnog, icecream soda Milk shake, eggnog, liqueur Bouillon, iced tea, hot tea, drink made from dry mix Water, iced tea, canned fruit drink Milk, eggnog, hot chocolate Milk, milk shake, ice cream soda, liqueur Prune juice, milk, light cream

Clean

Liqueur, apricot nectar, root beer Water, iced tea, wine

Drying

Hot chocolate, cranberry juice

Lingering

Hot chocolate, light cream, milk Water, hot tea

Cleansing

Water, milk, champagne Water, lemonade, cranberry juice Water, lemonade, ginger ale Milk, apricot nectar Buttermilk, hot chocolate, juice Water, apple cider, whiskey Water, ginger ale, bouillon Water, ginger ale, champagne Water, milk, club soda Buttermilk, beer, canned fruit drink Water Water, iced tea, club soda Milk, pineapple juice, juice

Source: Szczesniak (1979) in Food Texture and Viscosity by Malcolm C.Bourne

Perception of food and definition of the rheological terms Food Firmness (compression) Hardness (Bite) Cohesive Chewy, Fracturable (crispy/crunchy), Viscosity Sticky (tooth/palate), Tooth pack Dense/heavy, Airy/puffy/light Springy/rubbery

Terms Hardness Force to attain a given deformation Cohesiveness Degree to which sample deforms (rather than rupture) Adhesiveness Force required to remove sample from the surface Denseness Compactness of cross-section Springiness Rate of return to original shape after deformation


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It is evident from the above table that the sensory response of liquid food for consistency can be measured in term of rheological parameters. Various equipments have been designed to measure the consistency or viscosity or visco-elastic behaviour. In the early time the equipments were relatively simple and produce limited information but modern equipment are complex, accurate and more informative. CAPILLARY VISCOMETERS These are also known as glass capillary viscometers or Ostwald viscometers. Apparatus consists of an U shaped glass tube and a controlled temperature bath. One arm of viscometer consits a precise narrow bore or capillary inbetween two bulbs. The liquid is drawn into the upper bulb by suction, then allowed to flow down through the capillary into the lower bulb. The time taken for the liquid to pass the capillary is proportional to the kinematic viscosity. The voscometers are calibtrated using standard solutions of known viscosity and a conversion factor is calculated. The time taken by the test liquid to flow through a capillary of a known diameter is multiplied with the conversion factor of the viscometer to get the kinematic viscosity. Temperature is maintained be keeping the viscometers in a water bath. The capillary viscometer has been further classified depending of the specific end uses:

Zeitfuchs Cross-Arm Viscometers Newtonian liquids - 0.3 to 1,00,000 centistokes range. Suitability - Transparent or Opaque liquids Minimum sample volume - 15 mL Liquid bath depth - 292 mm Cannon-Fenske Routine Viscometers Newtonian liquids


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Suitability - Transparent or Opaque liquids Minimum sample volume - 7 mL Liquid bath depth - 203 mm Cannon-Fenske Opaque Viscometers Newtonian liquids - 30 to 6000 centistokes range. Suitability – very dark coloured liquids Minimum sample volume - 12 mL Liquid bath depth - 229 mm Ubbelohde Viscometers Newtonian liquids - 0.5 to 100,000 centistokes range. Suitability - Transparent or Opaque liquids Minimum sample volume - 11 mL Liquid bath depth - 241 mm Cannon-Ubbelohde Semi-Micro Viscometers Newtonian liquids - 0.5 to 100,000 centistokes range. Suitability - Transparent or Opaque liquids Minimum sample volume – 1.0 mL Liquid bath depth – 240 mm Cannon-Ubbelohde Dilution Viscometersg Information Newtonian liquids - 0.5 to 100,000 centistokes range. Suitability - Transparent or Opaque liquids Minimum sample volume - 8.0 mL Liquid bath depth - 280 mm

FALLING SPHERE VISCOMETERS The falling sphere viscometer is based on the Stokes' law, in which the fluid is stationary in a vertical glass tube while a sphere of known size and density is allowed to fall through the liquid. If correctly selected, it reaches terminal velocity, which can


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be measured by the time it takes to pass two marks on the tube. Electronic sensing can be used for opaque fluids. Knowing the terminal velocity, the size and density of the sphere, and the density of the liquid, Stokes' law can be used to calculate the viscosity of the fluid. A series of steel ball bearings of different diameter is normally used in the classic experiment to improve the accuracy of the calculation.

Falling ball viscometer

BOSTWICK CONSISTOMETER It consists of a rectangular channel with spring-operated gate on one side that allows a constant flow of the sample. There are two levelling screws for the fine adjustment of incination. There are 48 engraved graduations of 5 mm devisions of the floor of channel. The gate is closed and sample is loaded. The gate is opened and fluid is allowed to flow throgh the channel for one minutes. The distance travelled by the fluid is indicative of consistency.

Suitability - Liquid or paste-like materials Minimum sample volume - 75ml Dimensions - 76 x 140 x 356 mm


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ROTATIONAL VISCOMETERS Rotational viscometers use the idea that the torque required to turn an object in a fluid, can indicate the viscosity of that fluid. The common viscometer determines the required torque for rotating a disk or bob in a fluid at known speed. 'Cup and bob' viscometers work by defining the exact volume of sample which is to be sheared within a test cell and the torque required to achieve a certain rotational speed is measured. There are two classical geometries in "cup and bob" viscometers, known as either the "Couette" or "Searle" systems - distinguished by whether the cup or bob rotates. The rotating cup is preferred in some cases. 'Cone and Plate' viscometers use a cone of very shallow angle in bare contact with a flat plate. With this system the shear rate beneath the plate is constant to a modest degree of precision and deconvolution of a flow curve; a graph of shear stress (torque) against shear rate (angular velocity) yields the viscosity in a straightforward manner.

STABINGER VISCOMETER It is a modified Couette rotational viscometer where an accuracy comparable to that of kinematic viscosity determination is achieved. The internal cylinder in the Stabinger Viscometer is hollow and specifically lighter than the sample, thus floats freely in the sample, centered by centrifugal forces. The formerly inevitable bearing friction is thus fully avoided.

Stabinger viscometer The speed and torque measurement is implemented without direct contact, by a rotating magnetic field and an eddy current brake. This allows for a previously unprecedented torque resolution of 50 pN·m and an exceedingly large measuring range from 0.2 to 20,000 mPa·s with a single measuring system.


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STORMER VISCOMETER The Stormer viscometer is a rotation instrument used to determine the viscosity of paints, commonly used in paint industries. It consists of a paddle-type rotor that is spun by an internal motor, submerged into a cylinder of viscous substance. The rotor speed can be adjusted by changing the amount of load supplied onto the rotor. For example, in one brand of viscometers, pushing the level upwards decreases the load and speed, downwards increases the load and speed. The viscosity can be found by adjusting the load until the rotation velocity is 200 rotations per minute. By examining the load applied and comparing tables found on ASTM D 562, one can find the viscosity in Krebs units (KU), unique only to the Stormer type viscometer. This method is intended for paints applied by brush or roller. DYNAMIC RHEOMETER The two common approaches used in rotational rheometers are controlled rate and controlled stress. In the controlled rate approach, the material being studied is placed between two plates. One of the plates is rotated at a fixed speed and the torsional force produced at the other plate is measured. Hence, speed (strain rate) is the independent variable and torque (stress) is the dependent variable. In the controlled stress approach, the situation is reversed. A torque (stress) is applied to one plate and the displacement or rotational speed (strain rate) of that same plate is measured.

Controlled rate rheometer with Searle operation mode.


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Controlled stress rheometer with Searle operation mode

VIBRATIONAL VISCOMETER Vibrational viscometer operates by measuring the damping of an oscillating electromechanical resonator immersed in a fluid whose viscosity is to be determined. The resonator generally oscillates in torsion or transversely. The damping imposed on the resonator is directly realted to viscosity. The resonator's damping may be measured by one of several methods: • Measuring the power input necessary to keep the oscillator vibrating at a constant amplitude. The higher the viscosity, the more power is needed to maintain the amplitude of oscillation. • Measuring the decay time of the oscillation once the excitation is switched off. The higher the viscosity, the faster the signal decays. • Measuring the frequency of the resonator as a function of phase angle between excitation and response waveforms. The higher the viscosity, the larger the frequency changes for a given phase change. Vibrating viscometers are rugged industrial systems used to measure viscosity in the process condition. The active part of the sensor is a vibrating rod. The vibration amplitude varies according to the viscosity of the fluid in which the rod is immersed.


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These viscosity meters are suitable for measuring clogging fluid and high-viscosity fluids even with fibers even under extreme pH conditions. SENSORY EVALUATION AND INSTRUMENTAL MEASUREMENT The relationship between the sensory evaluation and instrumental measurement attributes has been studied by many workers like Hayakawa et al. 1995 (model emulsions), Hill et al. 1995 (lemon pie filling), Mela et al. 1994 (fat emulsions), Munoz & Sherman, 1990 (commercial salad dressings) and Peressini et al, 1998, Stern et al, 2001 (traditional and light mayonnaises). The relationship among rheological and sensory provided a good prediction of peak shear stress and peak time but gave only a crude prediction of stress decay. The study was found useful in modelling the human perception of fluid mechanics in the mouth.

CONCLUSIONS Rheological properties and mouth feel are determined by measuring force and deformation as a function of time. The rheological methods are useful if they correlate with the sensory properties of interest. The selection of tests depends on the type of food, the application, and the availability of suitable instrumentation, for testing the particular attributes of food material. However, the sensory response can not be completely duplicated by an instrumental procedure but it can provide a good prediction and modelling of fluid mechanics in the human masticatory system.

References Campanella, O.H. and Peleg, M. (1987). Analysis of the transient flow of mayonnaise in a coaxial viscometer. J. Rheol., 31, 439-452. Dickie, A.M. and Kokini, J.L. (1983). An improved model for food thickness from non-Newtonian fluid mechanics in the mouth. J. Food Sci., 48, 57-65. Figoni, P.I. and Shomaker, C.F. (1983). Characterization of time dependent flow properties of mayonnaise under steady shear. J. Texture Studies, 14, 431-442. Hayakawa, F., Tanisawa Y., Hatae, K. and Shimada, A. (1995). Relationship between the sensory evaluation for oiliness and physical properties in model emulsions. J. Home Econ. Jpn., 46, 765-774.


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Hill, M.A., Mitchell, J.R. and Sherman, P.A. (1995). The relationship between the rheological and sensory properties of a lemon pie filling. J. Texture Studies, 26, 457470. Kiosseoglou, V.D. and Sherman, P. (1983). Influence of egg yolk lipoproteins on the rheology and stability of O/W emulsions and mayonnaise. J. Texture Studies, 14, 397417. M.B. Sousa, W. Canet, M.D. Alvarez, C. Fernández (2007) Effect of processing on the texture and sensory attributes of raspberry (cv. Heritage) and blackberry (cv. Thornfree) Journal Food Engineering, 78, 9-21. Mela, J.D., Langley, K.R. and Martin, A. (1994). Sensory assessment of fat content : effect of emulsion and subject characteristics. Appetite, 22, 67-81. Munoz, J. and Sherman, P. (1990). Dynamic viscoelastic properties of some commercial salad dressings. J. Texture Studies, 21, 411-426. N. Lassoued, J. Delarue, B. Launay, C. Michon (2008) Baked product texture: Correlations between instrumental and sensory characterization using Flash Profile Journal of Cereal Science, 48,133-143. Peressini, D. Sensidoni, A. and de Cindio, B. (1998). Rheological characterization of traditional and light mayonnaises. J. Food Eng., 35, 409-417. Richardson, R.K., Morris, E.R., Ross-Murphy, S.B., Taylor, L.J. and Dea, I.C.M. (1989). Characterization of the perceived texture of thickened systems by dynamic viscosity measurements. Food Hydrocoll., 3, 175-191. S. Di Marzo, R. Di Monaco, S. Cavella, R. Romano, I. Borriello, P. Masi (2006) Correlation between sensory and instrumental properties of Canestrato Pugliese slices packed in biodegradable films. Trends in Food Science & Technology, 17, 4, 69-176. Stern, P., Valentova, H. and Pokorny, J. (2001). Rheological properties and sensory texture of mayonnaise. Eur. J. Lipid Sci. Technol., 103, 23-28. Wendin, K., Aaby, K., Edris, A., Ellekjaer, M.R., Albin, R., Bergenstahl, B., Johansson, L., Willers, E.P. and Solheim, R. (1997). Low-fat mayonnaise : influences of fat content, aroma compounds and thickness. Food Hydrocoll., 11, 87-99.


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NONDESTRUCTIVE METHODS FOR QUALITY EVALUATION OF DAIRY AND FOOD PRODUCTS

S. N. Jha Senior Scientist, Central Institute of Postharvest Engineering and Technology (CIPHET), Ludhiana – 141 004 Quality conscious consumers nowadays want to get assured about various quality attributes of food items before they purchase. Fruits, vegetables and milk are increasing in popularity in the daily diets in both developed and developing countries. Products’ quality and its measurement techniques are thus naturally extremely important. The decisions concerning the constituents, level of freshness, ripeness, and many other quality parameters are based mostly on subjective and visual inspection of the foods’ external appearance. Several nondestructive techniques for quality evaluation have been developed based on the detection of various physical properties that correlate well with certain factors of a product. The quality of foods including milk and milk products is mostly based on constituents, purity; i.e., levels of adulterants; color, gloss, flavor, firmness, texture, taste and freedom from external as well as internal defects. Numerous techniques for evaluating these parameters are now available commercially, but most of them are destructive in nature. Internal quality factors of fruits such as maturity, sugar content, acidity, oil content, and internal defects, however, are difficult to evaluate. Methods are needed to better predict the internal quality of fruits, vegetables, constituents of foods and level of adulterants, if any, without destroying the sample. Recently, there has been as increasing interest in nondestructive methods of quality evaluation, and a considerable amount of effort has been made in that direction. But the real problem is how these methods are to be exploited practically and what the difficulties are in implementing them. The objective of the present paper is thus to give exposure of recent nondestructive methods such as nuclear magnetic resonance, x-ray computed tomography, nearinfrared spectroscopy and some other important methods to the stakeholders of food industry in India and to evaluate their pros and cons for suitability in commercial application. Nuclear magnetic resonance (NMR) techniques The nuclear magnetic resonance technique, often referred as magnetic resonance imaging (MRI), involves resonant magnetic energy absorption by nuclei placed in an alternating magnetic field. The amount of energy absorbed by the nuclei is directly proportional to the number of a particular nucleus in the sample such as the protons in water oil. The theory of NMR is presented in detail elsewhere (Farrar & Becker, 1971). The basic concepts, types of pulsed experiments and the type of information that can be extracted from these experiments are described. Information


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on experimentation, assembling hardware, conducting laboratory tests and interpreting the results is also available from Fukushima and Roeder (1981). These authors also provided detailed theory for better understanding of what a scientist should seek and what he might expect to find out by using NMR. There are many applications of NMR in agriculture (Rollwitz, 1984). The simplest among them is the determination of moisture and oil content (Mousseri et al., 1974, Leung et al., 1976; Miller et al., 1980; Brosio et al., 1978; Rollwitz and Persyn, 1971). But the NMR response many times is not clear and poses problems especially when constituents other than water are present in the material (Steinberg & Richardson, 1996). Besides the established relationship between the moisture and output of NMR experiments, various other facts helpful in determining the quality of food materials without destroying them are available in the literature: Selections of chocolate confectionary products can be made non-invasively by three-dimensional magnetic resonance imaging (Miquel et al., 1998); using a spin echo pulse sequence, 128x64x64 data sets were acquired with either a 5-or 20-ms echo time, 500-ms repetition time and signal averages, in total 2-h scan time. Such images localize and distinguish between the constituents, and visualize both the internal and external structure of matter. Most perishable food products are now marketed in packaged form. To increase the marketability longer shelf life is needed and this is achieved by freezing and secondary processing of the food. During freezing it is natural that ice will form within the food that may change its characteristics. Ice formation during food freezing can be examined using the NMRI method as the formation of ice has been seen to reduce the spatially located NMR signal. The characteristics of a food can be better controlled as MRI can serve to assess freezing times and the food structure during the freezing process (Kerr et al., 1998). The secondary processing changes almost all characteristics of a food, such as physical and aerodynamic (Jha & Kachru, 1998), thermal and hygroscopic properties (Jha & Prasad, 1993; Jha 1999), which in turn, change its key acceptability factors, i.e. sensory texture and taste. The sensory texture of cooked food such as potatoes has been predicted using the NMRI technique (Thybu et al., 2000). In addition, NMR image intensity, the ratio of the oil and water resonance peaks of the one-dimensional NMR spectrum, and both the spin-lattice relaxation time and spin-spin relaxation time of water in the fruit are correlated with maturity of a fruit like avocado before harvesting (Chen et al., 1993). This important finding has desirable features for high speed sorting using a surface-coil NMR probe that determine the oil/water resonance peak ratio of the signal from one region in an intact fruit. An on-line nuclear magnetic resonance quality evaluation sensor has recently been designed, constructed and tested (Kim et al., 1999). The device consists of a super-conducting magnet with a 20mm diameter surface coil and a 150 mm diameter imaging coil coupled to a conveyor system. These spectra were used to measure the oil/water ration in avocados and this ratio correlated to percent dry weight. One Sensory and Related Techniques for Evaluation of Dairy Foods

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dimensional magnetic resonance images of cherries were later used to detect the presence of pits inside. X-ray and computerized tomography (CT) X-ray imaging is an established technique to detect strongly attenuating materials and has been applied to a number of inspection applications within the agricultural and food industries. In particular, there are many applications within the biological sciences where we wish to detect weakly attenuating materials against similar background material. X-ray computed tomography (CT) has been used to image interior regions of apples with varying moisture and, to a limited extent, density states (Tollner et al., 1992). The images were actually maps of x-ray absorption of fruit cross sections. Xray absorption properties were evaluated using normal apples alternatively canned and sequentially freeze-dried, fruit affected by water core disorder, and normal apples freeze-dried to varying levels. The results suggested that internal differences in x-ray absorption within scans of fruit cross-sections are largely associated with differences in volumetric water content. Similarly, the physiological constituents have been monitored in peaches by CT methods in which x-ray absorbed by the peaches is expressed in CT number and used as an index for measuring the changes in internal quality of the fruit (Barcelon et al., 1999). Relationships between the CT number and the physiological contents were determined and it was concluded that x-ray CT imaging could be an effective tool in the evaluation of peach internal quality. In another study, the potential for Compton scattered x-rays in food inspection was evaluated by imaging the density variation across a food material by measuring the Compton scatter profile across a food material by measuring the Compton scatter profile across polystyenespheres with internal voids (MacFarlane et al., 2000). In this study particular attention was paid to simulate the obscuring influence of multiple scatter. The simulated result was found to be in close agreement with the experimental observation. Some experimental test sample of a Perspex block with various embedded soft materials showed that care should be taken to ensure that the transmission image is taken with x-ray within an appropriate energy range (Zwiggelaar et al., 1997). For low Z materials the contrasts between the materials became more pronounced at lower x-ray energies. If more than one soft material has to be distinguished from the surrounding area it may be advantageous to image over a range of x-ray energies. Visual spectroscopy and colour measurements Colour measurement is now little bit old technique to check the quality of any items in terms of appearance. It has also been tested for assessing the ripeness of fruits and measurement of aesthetic appearances of dairy products. Recently many works have been reported to correlate the internal quality such as total soluble solids contents, maturity of fruits in tree and sweetness of intact fruits using Hunter colour values and reflectance spectra in visual range of wavelengths (Jha et al, 2005 and


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2006). This in fact is possible through rigorous analysis of data and modeling for a huge number of samples of varied nature. Near-infrared spectroscopy The use of near-infrared spectroscopy as rapid and often nondestructive technique for measuring the composition of biological materials has been demonstrated for many commodities. This method is no longer new; as it started in early 1970 in Japan (Kawano, 1998), Just after some reports from America. Even an official method to determine the protein content of wheat is available (AACC, 1983). The National Food Research Institute (NFRI), Tsukuba has since become a leading institute in NIR research in Japan and has played a pivotal role in expanding nearinfrared spectroscopy technology all over the country (Iwamoto et al., 1995). In Japan, NIR as a nondestructive method for quality evaluation was started for the determination of sugar content in intact peaches, Satsuma orange and similar other soluble solids (Kawano, 1994). To determine the solid content of cantaloupe Dull et al. (1989) used NIR light at 884 nm and 913 nm. Initially the correlation of their findings was poor mainly due to light losses. Later, Dull and Birth (1989) modified the earlier method and applied it to honey-dew melons; the improved methods showed better correlation. Similarly, a nondestructive optical method for determining the internal quality of intact peaches and nectarines was investigated (Slaughter, 1995). Based upon visible and nearinfrared spectrophotometer techniques, the method was capable of simultaneously predicting the soluble solid content, sucrose content, sorbitol content, etc. of intact peaches and nectarines was investigated (Slaughter, 1995). Based upon visible and near-infrared spectrophotometer techniques, the method was capable of simultaneously predicting the soluble solid content, sucrose content, sorbitol content, etc. of intact peaches and nectarines, and required no sample preparation. Now various NIR spectrometers are available and are being used commercially. Some modifications in these available spectrometers, especially for holding the intact samples, are reported (Kawano et al., 1992; 1993). In the same sample holding a test tube for holding liquid food such as milk was also used to determine fat content (Chen et al., 1999). Recently a low cost NIR spectrometer has been used to estimate the soluble solids and dry matter content of kiwifrui (Osborne & Kunnemeyer, 1999). Errors are within the permissible limit and the time requires for obtaining data has been reduced. The influence of sample temperature on the NIR calibration equation was also evaluated and a compensation curve for the sample temperature was developed (Kawano et al., 1995) to rectify the result.

Now detection of almost all adulterants in milk in single stroke (Jha and matsuoka, 2004) and composition of milk and effect of somatic cell count on determination of milk constituents are very accurately determined ( Tsenkova et al


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2001). Similarly taste of tomato juice in terms of acid-brix ratio can be determined with high accuracy (Jha and Matsuoka 2004). NIR spectroscopy in fact is the most suited technique for nondestructive analysis of dairy products. Miscellaneous techniques Quality attributes such as invisible surface bruises, color, gloss, firmness, density, volume expansion of processed food etc are also important (Jha & Prasad, 1996). Often consumers select food materials, particularly fruits and vegetables by judging these parameters visually. Multiple efforts have been made to determine these parameters visually. A fluorescence technique was used to detect invisible surface bruises on Satsuma mandarins (Uozumi et al., 1987). The authors have also tested this method successfully to know the freshness of cucumbers and eggs and found it very useful for detecting the freshness of agricultural produce. Matsuoka et al., (1995) measured the gloss of eggplant by a spectral radiometer system and found or to be a viable parameter for determining freshness. They observed remarkable change in relative spectral reflectance values after 48 h. Later, they compares their evaluation by eye in a sorting house with the integrated results of relative spectral reflectance in the visible range and found that the gloss on the surface differs with light and is caused by round and adhesives substances on the epidermal cells (Matsuoka et al., 1996). A unique gloss meter for measuring the gloss of curved surfaces was used in parallel with a conventional, flat surface gloss meter to measure peel gloss of ripening banana (Ward & Nussinovitch, 1996). Usually banana ripeness is judged by the color of the peel. The new gloss meter is able to measure the peel correctly which helps in predicting the correct time and level of ripening. This is also able to measure the gloss of other fruits and vegetables such as green bell pepper, orange, tomato, eggplant and onion (Nussinovitch et al., 1996). Glossiness and color, in fact, are the only visual attributes for measuring the quality of fruits and vegetables. Another property that helps a consumer in deciding the quality is firmness. Takao (1998) developed a fruit hardness tester that can measure the firmness of kiwifruit nondestructively. The tester is called a ‘HIT counter’ after the three words, hardness, immaturity and texture. By just setting the sample in the tester, the amount of change in shape is measured and a digital reading within a few seconds indicates about the freshness. Based on the same principal another on-line prototype HIT counter, fruit hardness sorting machine has also been developed (Takao & Omori, 1991). The relationship between density and internal quality of watermelon can also be determined. An optimum range of density was first determined and then a new automatic density sorting system was develops and then a new automatic density sorting system was developed to measure the hollowness of a watermelons with cavities or deteriorated porous flesh to be removed and permits estimation of the soluble solid content of this fruits. Using gloss and other physical parameters such as stiffness and density, Jha and Matsuoka, 2002 have also determined the freshness of eggplants and have correlated it very easily with the day to day price in vegetable mandis. Sensory and Related Techniques for Evaluation of Dairy Foods

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Neural networks have lately gained in popularity as an alternative to regression models to regression models to characterize the biological process. Their decision-making capabilities can best to used in image analysis of biological products where the shape and size classification is not governed by any mathematical function. Many neural network classifiers have been used and evaluated for classifying agricultural products, but multi-layer neural network classifiers perform such tasks best (Jayas et al., 2000). Recently one scientist used a gamma- absorption techniques combined with a scanning device for continuous non-destructive crop mass and growth measurement in the field (Gutezeit, 200). Most important in this study was the accuracy of the measurement, which was found to be in agreement with the direct weighting system. This method has made it possible to assess the reaction of plants and their dependence on environmental factors by growth analysis. Conclusions Determination of quality of any food material including milk and milk products is actually a complex problem that requires a variety of specific sensor, more than an accumulation of simple sensor. Various techniques are being tried. IMR, x-ray CT and NIR techniques may be useful for a large volume of work in agriculture, especially for evaluation of qualities such as maturity, internal quality of fruit and conditions of food materials after processing, level of adulterants and useful constituents. These techniques, although give a correct picture and precise measurement of parameters, are not convenient for small business except NIR and visual spectroscopy. Their high cost restricts application to large entrepreneurs and developed countries only. Two examples of the use of x-ray imaging relevant to the agricultural and food industries have been given, notably in the inspection of vegetables and food materials using low energy x-ray imaging and in the inspection and control of dynamic processes. The x-ray imaging results have been compared with the full threedimensional information obtained by computer tomogrphy. The CT results show more detail in the test sample than the single transmission image and detail in the inspection of materials of variable shape usually encountered in the agricultural and food industry. The imaging techniques MRI and x-ray CT are able to show only the internal structure of the material, not the compositional of nutritional details, whereas NIR and visual spectroscopy techniques are very successfully being used to determine the compositional quality of a food and can be used even at farm. However, it is not yet possible to produce an image of the internal physical quality of fruits and vegetables. All techniques are costly because most of the expertise is imported. Central Institute of Post-harvest Engineering and Technology (CIPHET), Ludhiana has taken the lead by initiating R & D works in the country about four years ago. Dairy and food processing industries and other research organizations should also work together to develop such type of instrumentation indigenously. References Sensory and Related Techniques for Evaluation of Dairy Foods

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American Association of Cereal Chemists. (1983). Approved methods of the Am. Assoc. of Cereal Chemists, 8th Ed. (March. St. Paul, Minn. Barcelon, E.G., Tojo, S. and watanable, K. (1999). X-ray computed tomography for internal quality evaluation of peaches. J. Agric. Eng. Res., 73, 323-330. Brosia , E.F., Conti, C.L. and Sykara, S. (1978). Moisture determination in starch-rich food products by pulsed nuclear magnetic resonance. J. Food Technol., 13, 107-116. Chen, J.Y., Iyo, C. and Kawano, S. (1999). Development of calibration with sample cell compensation for determining the fat content of unhomogenised raw milk by a simple near infrared transmittance method. J. Near Infrared Spectosc., 7, 265-273. Chen, P., McCarthy, M.J., Kauten E., Sarig, Y. and Han, S. (1993). Maturity evaluation of avocados by NMR methods. J. Agric. Eng. Res., 55, 177-187. Dull, G.G. and Birth, G.S. (1989). Nondestructive evaluation of fruit quality: Use of near infrared spectrophotometry to measure solube solids in intact honeydew melons. Hortscience, 24, 754. Dull, G.G. and Birth, G.S. Smittle, D.A and Leffler, R.G. (1989). Near infrared analysis of soluble solids in intact cantaloupe. J. Food Sci., 54, 393-395. Farrar, T.C. and Becker, E.D. (1971). Pulse and Fourier Transform NMR: Introduction to Theory and Methods. Academic Press, New York. Fukushima, E. and Roeder, S.B.W. (1981). Experimental Pulse NMR. AddisonWasley Publishing Company, Reading, M.A. Gutezeit, B. (2000). Non-destructive measurement of fresh plant mass by the gammascanning technique applied to broccoli. J. Agric. Eng. Res., 75, 251-255. Iwamoto, M., Kawano, S. and Yukihiro, O. (1995). An overview of research and development of near infrared spectroscopy in Japan. J. Near Infrared Spectrosc., 3, 179-189. Jayas, D.S., Paliwal, J and Visen, N.S. (2000). Multi-layer neural networks for image analysis of agricultural products. J. Agric. Eng. Res. (in press). Jha, S. N. and Matsuoka T. (2002). Development of freshness index of eggplant. Applied Engineering in Agriculture, ASAE, 18 (5): 57-60. Jha, S. N. and Matsuoka, T. (2004). Detection of adulterants in milk using near infrared spectroscopy. Journal of Food Science and Technology, 41(3), 313 – 316. Jha, S. N. and Matsuoka, T. (2004). Nondestructive determination of acid brix ratio (ABR) of tomato juice using near infrared (NIR) spectroscopy. International Journal of Food Science and Technology, 39(4): 425 - 430. Jha, S. N.; Chopra, S. and Kingsly, ARP (2005). Determination of sweetness of intact mango using spectral analysis. Biosystems Engineering, 91(2), 157 – 161. Jha, S.N, Chopra S., and Kingsly, ARP (2006). Modeling of color values for nondestructive evaluation of maturity of mango. Journal of Food Engineering. – in press. Jha, S.N. (1999). Physical and hygroscopic properties of makhana. J. Agric. Eng. Res., 72 , 145-150.


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Jha, S.N. and Prasad, S. (1993). Physical and thermal properties of gorgon nut. J. Food Process Eng., 16, 237-245. Jha, S.N. and Prasad, S. (1996). Determination of processing conditions of gorgon nut (Euryale ferox). J. Agric. Engg. Res., 63, 103-112. Jha, S.N. Matsuoka T. (2000). Review: Nondestructive Techniques for quality evaluation of intact fruits and vegetables. Food Science and Technology Research, 6(4), 248 – 251. Jha. S. N. and Kachru, R.P. (1998). Physical and aerodynamic properties of makhana. J.Food Process.Eng., 79, 301-316. Kato, K. (1997). Electrical density sorting and estimation of soluble solids contents of watermelon. J. Agric. Engg. Res., 67, 161-170. Kawano, S. (1994). Nondestructive near infrared quality evaluation of fruits and vegetables in Japan. NIR News, 5, 10-12. Kawano, S. (1998). New application of nondestructive methods for quality evaluation of fruits and vegetables in Japan. J. Jpn. Soc. Hort. Sci., 67, 1176-1179. Kawano, S., Abe, H. and Iwamoto, M. (1995). Development of a calibration equation with temperature compensation for determining the brix value in intact peaches. J. Near infrared Spectrosc., 3, 211-218. Kawano, S., Fujiwara, T., and Iwamoto, M.C. (1993). Nondestructive determination of sugar content in satsuma maddarin using NIR transmittance. J. Jpn. Soc. Hort. Sci., 62, 465-470. Kawano, S., Watanabe, H. and Iwamoto, M. (1992). Determination of sugar content in intact peaches by near infrared spectroscopy with fibre optics in interactance mode. J. Jpn. Soc. Hort. Sci., 61, 445-451. Kerr, W.L., Kauten, R.J., McCarthy, M.J. and Reid, D.S. (1998). Monitoring the formation of ice during food freezing by magnetic resonance sensors. J. Agric. Eng. Res., 74, 293-301. Kim, S.M., Chen, P., McCarthy, M.J. and Zoin, B., (1999). Fruit internal quality evaluation using on-line nuclear magnetic resonance sensors. J. Agric. Eng. Res., 74, 293-301. Leung, H.K., Steinberg, M.P. Wei, L.S. and Nelson, A.I. (1976). Water binding of macromolecules determined by pulsed NMR. J. Food Sci., 41, 297-300. Macfarlane, N.J.B., Bull, C.R., Tillett, R.D., Speller, R.D., Royle, G.J and Johnson, K.R.A. (2000). The potential for compton scattered x-rays in food inspection: The effect of multiple scatter and sample inhomogeneity. J. Agric. Eng. Res., 75, 265-274. Matsuoka, T., Miyauchi, K. and Sun, D. (1995). Basic studies on the quality evaluation of agricultural products-Quantification of gloss of eggplants by spectral characteristics. J. Jpn. Sci. Agric Mach., 57, 33-40. Matsuoka, T., Miyauchi, K. and Yano, T. (1996). Basic studies on the quality evaluation of agricultural products (Part 2)- The evaluation of colour and gloss decrease on the surface of eggplants. J. Jpn. Sci. Agric. Mach., 58, 69-77.


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Miller, B.S., Lee, M.S., Hughes, J.W. and Pomernz, Y. (1980). Measuring high moisture content of cereal grains by pulsed nuclear magnetic resonance. Cerreal. Cereal Chem., 57, 126-129. Miquel, M.E., Evans, S.D. and Hall. L.D. (1998). Three dimensional imaging of chocolate confectionary by magnetic resonance methods. Food Sci. technol., 31, 339343. Mousseri, J., Steinberg, M.P., Nelson, A.I. and Wei, L.S. (1974). Bound water capacity of corn starch and its derivatives by NMR, J. Food Sci., 39, 114-116. Nussinovitch, A., Ward, G. and Mey-tal, E. (1996). Gloss of fruits and vegetables. Food Sci. Technol., 29, 184-186. Osborne, S.D. and Kunnemeyer, R. (1999). A low cost system for the grading of kiwifruit. J. Near Infrared Spectocs., 7, 9-15. Rollwitz, W.L. (1984). Radio frequency spectroscopy: Versatile sensors for agriculture applications. ASAE Paper No. 84-1590, ASAE. St. Joseph, MI 49085. Rollwitz, W.L. and Persyn, G.A. (1971). On-stream NMR Measurements and control. Am. Oil Chem. Soc. J., 48, 59-66. Slaughter, D.C. (1995). Nondestructive determination of internal quality in peaches and nectarines. Trans, ASAE, 38, 617-623. Tsenkova, R; Atanassova, S.; Ozaki, Y.; Toyoda, K.; and Itoh, K. (2001). NearInfrared spectroscopy for biomonitoring; influence of somatic cell count on cow’s milk composition analysis. International Dairy Journal 11 (2001) 779-783. Steinberg, M.P. and Richardson, S.J. (1986). Application of nuclear magnetic resonance. Paper No.11. Presented at the International Union Food Science and Technology Symposium on Water Activity: Theory and Application. June 13-14, Dallas, TX. Takao, H. (1988). HIT counter. Noryu Giken Kaihou, 180, 7-9 (in Japanese). Takao, H. and Omori, S. (1991). Quality evaluation of fruits and vegetables using light transmittance. Noryu Giken Kaihou, 145, 14-16 (in Japanese). Thybo, A.K., Bechmann, I.E., Martens, M. and Engelsen, S.B. (200). Prediction of sensory texture of cooked potatoes using uniaxial compression, near infrared spectroscopy and low field H NMR Spectroscopy. Food Sci. Technol., 33, 103-111. Tollner, E.W., Hung, Y.-C., Upchurch, B.L. and Prussia, S.E. (1992). Relating x-ray absorption to density and water content in apples. Trans. ASAE, 35, 1921-1928. Uozumi, J., Kawano, s., Iwamoto, M. and Nishnari, K. (1987). Spectrometric system for the quality evaluation of unevenly couloured food. Nippon Shokuhin Kagyo Gakkaishi, 34, 163-170 (in Japanese). Ward, G. and Nussinovitch, A. (1996). Peel as a indicator for banana ripeness. Food Sci. Techol., 29, 289-294. Zwiggelaar, R., Bull, C.R., Mooney, M.J. and Czarnes, S. (1997). The detection of soft materials by selective energy x-ray transmission imaging and computer tomography. J. Agric. Eng. Res., 66, 203- 21.


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GOOD LABORATORY PRACTICES – GENESIS & CONCEPT

Dr. Rajan Sharma Senior Scientist, Dairy Chemistry Division, National Dairy Research Institute, Karnal. (E-mail. [email protected]) The economic and social implications of new technologies are closely linked with newer chemicals. Chemicals, be they industrial chemicals, pharmaceuticals, veterinary drugs, pesticides, cosmetic products, food products, feed additives, etc., are required to be evaluated to determine their potential hazards. A number of countries require manufacturers of these chemicals to establish through data that use of these products do not pose any hazards to human health and the environment. Nonhazardous nature of these substances needs to be established through studies and data, which will be examined by the regulatory authorities of the concerned countries. Good Laboratory Practice (GLP) is a system, which has been evolved by Organization for Economic Co-operation and Development (OECD) used for achieving the above goals. GLP generally refers to a system of management controls for laboratories and research organizations to ensure the consistency and reliability of results as outlined in the OECD Principles of GLP and national regulations. GLP applies to non-clinical studies conducted for the assessment of the safety of chemicals to man, animals and the environment. The internationally accepted definition is as follows: GLP is a quality system and the manner in which non-clinical safety studies are: planned, performed, monitored, recorded, reported and archived. These studies are undertaken to generate data by which the hazards and risks to users, consumers and third parties, including the environment, can be assessed for pharmaceuticals, agrochemicals, cosmetics, food and feed additives and contaminants, novel foods and biocides. GLP helps assure regulatory authorities that the data submitted are a true reflection of the results obtained during the study and can therefore be relied upon when making risk/safety assessments. History of GLP The formal concept of ‘GLP’ first evolved in the USA in the 1970s because of concerns about the validity of preclinical safety data submitted to the Food and Drug Administration (FDA) in the context of new drug applications. The inspection of studies and test facilities had yielded indications for, and instances of, inadequate planning and incompetent execution of studies, insufficient documentation of methods and results, and even fraud. For example, replacing animals which died during a study by new ones (which had not been treated appropriately with the test compound)


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without documenting this fact; taking haematology data for control animals from control groups not connected with the study; deleting necropsy observations because the histopathologist received no specimens of lesions; or re-correcting discrepancies in raw data and final report tables by juggling around the raw data in order to ‘fit the results tables’ to the final report. These deficiencies were made public in the so-called Kennedy Hearings of the US Congress, and the outcome of these subsequently led to the publication, by the FDA, of Proposed Regulations on GLP in 1976, with the respective Final Rule coming into effect in June 1979.These regulations were intended to provide the regulatory basis for assurance that reports on studies submitted to the FDA would reflect faithfully and completely the experimental work carried out. In the chemical and pesticide field, the US Environmental Protection Agency (EPA) had encountered similar problems with study quality and issued its own draft GLP regulations in 1979 and 1980, publishing the Final Rules in two separate volumes in 1983. OECD and GLP On the international level, the OECD, in order to avoid non-tariff barriers to trade in chemicals, to promote mutual acceptance of non-clinical safety test data, and to eliminate unnecessary duplication of experiments, followed suit by assembling an expert group who formulated the first OECD Principles of GLP. Their proposals were subsequently adopted by the OECD Council in 1981 through its “Decision Concerning the Mutual Acceptance of Data in the Assessment of Chemicals” [C(81)30(Final)], in which they were included as Annex II. In this document, the Council decided that data generated in the testing of chemicals in an OECD member country in accordance with the applicable OECD Test Guidelines and with the OECD Principles of GLP shall be accepted in other member countries for purposes of assessment and other uses relating to the protection of man and the environment. It was soon recognized that these Principles needed explanation and interpretation, as well as further development, and a number of consensus workshops dealt with various issues in subsequent years. The outcome of these workshops was then published by OECD in the form of consensus documents. After some 15 years of successful application, the OECD Principles were revised by an international group of experts and were adopted by the OECD Council on 26th November 1997 [C(97)186/Final] by a formal amendment of Annex II of the 1981 Council Decision. A number of OECD member countries have adopted these Principles in their national legislation, notably the amendment of the European Union in Commission Directive 1999/11/EC of 8 March, 1999 to the Council Directive 87/18/EEC of 18 December, 1986, where GLP had first been introduced formally into the European legislation. Internationally, the observance of GLP has thus been defined as a prerequisite for the mutual acceptance of data, which means that different countries or regulatory authorities accept laboratory studies from other countries as long as they follow the internationally accepted GLP Principles. This mutual acceptance of safety test data will also prevent the unnecessary repetition of studies carried out in order to comply with any single


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country’s regulations. In order to facilitate further the mutual acceptance of data and to extend this possibility to outside countries, the OECD Council adopted, on 26 November 1997, the ‘Council Decision concerning the Adherence of Non-member Countries to the Council Acts related to the Mutual Acceptance of Data in the Assessment of Chemicals’ [C(81)30(Final) and C(89)87(Final)] [C(97)114/Final], wherein interested non-member countries are given the possibility of voluntarily adhering to the standards set by the different OECD Council Acts and thus, after satisfactory implementation, to join the corresponding part of the OECD Chemicals Programme. Mutual acceptance of conformity of test facilities and studies with respect to their adherence to GLP, on the other hand, necessitated the establishment of national procedures for monitoring compliance. According to the OECD Council ‘Decision-Recommendation on Compliance with Principles of GLP’ of 2 October 1989 [C(89)87(Final)], these procedures should be based on nationally performed laboratory inspections and study audits. The respective national compliance monitoring authorities should exchange not only information on the compliance of test facilities inspected, but should also provide relevant information concerning the countries’ procedures for monitoring compliance. Although devoid of such officially recognized national compliance monitoring authorities, some developing countries do have an important pharmaceutical industry, where preclinical safety data are already developed under GLP. In these cases, individual studies are – whenever necessary – audited by foreign GLP inspectors (e.g. of FDA, the Netherlands or Germany). Principles of Good Laboratory Practice The purpose of these Principles of GLP is to promote the development of quality test data. Comparable quality of test data forms the basis for the mutual acceptance of data among countries. If individual countries can confidently rely on test data developed in other countries, duplicative testing can be avoided, thereby saving time and resources. The Principles of GLP have been developed to promote the quality and validity of test data used for determining the safety of chemicals and chemical products. It is a managerial concept covering the organizational process and the conditions under which laboratory studies are planned, performed, monitored, recorded and reported. Its principles are required to be followed by test facilities carrying out studies to be submitted to national authorities for the purposes of assessment of chemicals and other uses relating to the protection of man and the environment. The application of these Principles will help to avoid the creation of technical barriers to trade, and further improve the protection of human health and the environment. There are ten principles of GLP that have been framed by OECD and complete text regarding these principles can be accessed from http://www.oecd.org/document/63/0,2340,en_2649_ 34381_23461751_1_1_1,00.html. These principles in brief are as follows:


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1. Test Facility Organization and Personnel Each test facility management should ensure that these Principles of GLP are complied with in its test facility. It should ensure that a statement exists which identifies the individual(s) within a test facility who fulfill the responsibilities of management as defined by these Principles of GLP; ensure that a sufficient number of qualified personnel, appropriate facilities, equipment, and materials are available for the timely and proper conduct of the study; ensure the maintenance of a record of the qualifications, training, experience and job description for each professional and technical individual. For each study, a study director should be appointed. The Study Director is the single point of study control and has the responsibility for the overall conduct of the study and for its final report. 2. Quality Assurance Programme The test facility should have a documented Quality Assurance Programme to assure that studies performed are in compliance with these Principles of GLP. The Quality Assurance Programme should be carried out by an individual or by individuals designated by and directly responsible to management and who are familiar with the test procedures. This individual(s) should not be involved in the conduct of the study being assured. 3. Facilities The test facility should be of suitable size, construction and location to meet the requirements of the study and to minimize disturbance that would interfere with the validity of the study. The design of the test facility should provide an adequate degree of separation of the different activities to assure the proper conduct of each study. The test facility should have facilities for handling test and reference item, archive facilities, waste disposal etc. 4. Apparatus, Material, and Reagents Apparatus, including validated computerized systems, used for the generation, storage and retrieval of data, and for controlling environmental factors relevant to the study should be suitably located and of appropriate design and adequate capacity. Apparatus used in a study should be periodically inspected, cleaned, maintained, and calibrated according to Standard Operating Procedures. Records of these activities should be maintained. Calibration should, where appropriate, be traceable to national or international standards of measurement. Apparatus and materials used in a study should not interfere adversely with the test systems. Chemicals, reagents, and solutions should be labeled to indicate identity (with concentration if appropriate), expiry date and specific storage instructions. Information concerning source, preparation date and stability should be available. The expiry date may be extended on the basis of documented evaluation or analysis. 5. Test Systems Sensory and Related Techniques for Evaluation of Dairy Foods

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Apparatus used for the generation of physical/chemical data should be suitably located and of appropriate design and adequate capacity. The integrity of the physical/chemical test systems should be ensured. Proper conditions should be established and maintained for the storage, housing, handling and care of biological test systems, in order to ensure the quality of the data. 6. Test and Reference Items Records including test item and reference item characterization, date of receipt, expiry date, quantities received and used in studies should be maintained. Handling, sampling, and storage procedures should be identified in order that the homogeneity and stability are assured to the degree possible and contamination or mix-up are precluded. Storage container(s) should carry identification information, expiry date, and specific storage instructions. Each test and reference item should be appropriately identified (e.g., code, Chemical Abstracts Service Registry Number [CAS number], name, biological parameters). 7. Standard Operating Procedures A test facility should have written Standard Operating Procedures approved by test facility management that are intended to ensure the quality and integrity of the data generated by that test facility. Revisions to Standard Operating Procedures should be approved by test facility management. Each separate test facility unit or area should have immediately available current Standard Operating Procedures relevant to the activities being performed therein. Published text books, analytical methods, articles and manuals may be used as supplements to these Standard Operating Procedures. Deviations from Standard Operating Procedures related to the study should be documented and should be acknowledged by the Study Director and the Principal Investigator(s), as applicable. 8. Performance of the Study For each study, a written plan should exist prior to the initiation of the study. The study plan should be approved by dated signature of the Study Director and verified for GLP compliance by Quality Assurance personnel. The study plan should also be approved by the test facility management and the sponsor, if required by national regulation or legislation in the country where the study is being performed. 9. Reporting of Study Results A final report should be prepared for each study. In the case of short term studies, a standardized final report accompanied by a study specific extension may be prepared. Reports of Principal Investigators or scientists involved in the study should be signed and dated by them. The final report should be signed and dated by the Study Director to indicate acceptance of responsibility for the validity of the data. The extent of compliance with these Principles of GLP should be indicated.


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10. Storage and Retention of Records and Materials The following should be retained in the archives for the period specified by the appropriate authorities: a) the study plan, raw data, samples of test and reference items, specimens, and the final report of each study; b) Records of all inspections performed by the Quality Assurance Programme, as well as master schedules; c) records of qualifications, training, experience and job descriptions of personnel; d) records and reports of the maintenance and calibration of apparatus; e) validation documentation for computerized systems; f) the historical file of all Standard Operating Procedures; g) environmental monitoring records. Material retained in the archives should be indexed so as to facilitate orderly storage and retrieval. Only personnel authorized by management should have access to the archives. Movement of material in and out of the archives should be properly recorded. If a test facility or an archive contracting facility goes out of business and has no legal successor, the archive should be transferred to the archives of the sponsor(s) of the study(s). GLP in India The Indian test facilities, involved in safety studies have been appraising concerned Government Departments(s) for the need of having a system of GLP certification whereby they can demonstrate their capabilities, to a third-party as per the international norms. Few of the Indian laboratories have even obtained GLPcompliance certification based on OECD Principles of GLP from OECD member countries to meet their pressing needs. However, it partly served their purpose as such as a GLP certification is not acceptable in remaining OECD member countries because it lacks the Indian commitment for mutual acceptance. National GLP Compliance Monitoring Authority was established by the Department of Science & Technology, Government of India, with the approval of the Union Cabinet on April 24, 2002. Presently, India enjoys the status of a provisional member of the OECD for GLP. India is an Observer to the OECD’s Working Group on GLP and also a member of the OECD Test Guidelines Programme. The aim is be to get the status of full membership in the near future so that the Indian industries do not have to get their test facility (products) certified from safety angle by other GLP monitoring authorities and do not lose on the trade front. The National GLP Programme functions through an Apex Body, which has Secretaries of concerned Ministries/Departments, Director-General, CSIR and the Drugs Controller General of India as its members with Secretary-DST as its Chairman. This Apex Body is responsible to ensure that the National GLP Programme functions as per OECD norms and principles. The Apex Body is supported by Technical Committee on GLP, National Coordination Committee for OECD Test Guidelines Programme and Legislation Committee to enact a national


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legislation on GLP. The Authority has trained 33 experts in the country as GLP inspectors. GLP-compliance certification is voluntary in nature. Industries/test/ facilities/laboratories dealing with chemicals and looking for approval from regulatory authorities before marketing them, may apply to the National GLP Compliance Monitoring Authority for obtaining GLP Certification for one or more of the following areas of expertise: • • • • • • • • •

physical-chemical testing toxicity studies mutagenicity studies environmental toxicity studies on aquatic and terrestrial organisms studies on behaviour in water, soil and air bio-accumulation, residue studies studies on effects on mesocosms and natural ecosystems analytical and clinical chemistry testing Others

The test facilities/laboratories have to apply in the prescribed application form. After the application for GLP certification is received, a pre-inspection of the laboratory is carried out by the GLP inspectors, followed by a final inspection. The report, prepared by the inspection team, is put to the Technical Committee for recommendation to Chairman, National GLP-Compliance Monitoring Authority. GLP-compliance Certification is valid for a period of three years and the GLP Secretariat organizes annual surveillance and a re-assessment during third year for maintaining the certification. Application of GLP concept in food and dairy laboratories The essential quality elements in the food industry are stability, safety, wholesomeness and purity of the products. The requirements generally applied to food/dairy production originate from legislative governmental standards in different countries, specifications in international markets, and consumers’ and customers’ needs. The food laboratories are generally involved in two distinct types of operations, each with defined responsibilities. The responsibility of the laboratory situated in a factory is to control the quality of the production and the products. The functions of the laboratory are an essential part of the manufacturing process, and also an important sector of good manufacturing practices. The success in good manufacturing practices and critical control point surveillance depends on the reliability, adequate and accuracy of the analytical work of the laboratory. Prerequisite for high quality manufacture is the certainty that the laboratory has the capacity and is able to use proper and appropriate


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analysing techniques, to ensure that the results are correct and fulfill the requirement of accuracy, reproducibility and repeatability. This can be achieved by following the guidelines of ISO 17025 followed by the accreditation of the laboratory which provides formal recognition to competent laboratories. However, for a research and development (R & D) laboratory, working under GLP environment by following the principles of GLP is a good proposition. R & D laboratory are generally entrusted with the job of product development, identification of health benefits of a particular food, isolation of some health promoting factors/constituents from the food, identification of new technological parameters for alternative processing of raw material etc. GLP studies must be fully documented (methods, procedures, deviations), which means that they can be accurately repeated at any time in the future. The full documentation of the studies, from planning activities right through to the production of reports, means that all the activities of the study are traceable and therefore the study may be audited by third parties. Since GLP is an internationally accepted standard for the organization of studies, performing such experiments with compliance to GLP promotes their acceptance world-wide. In case of any dispute, the GLP documentation may be of great help for the validation of any claim made by R & D laboratory. Conclusion The purpose of these Principles of GLP is to promote the development of quality test data and to provide a managerial tool to ensure a sound approach to the management, including conduct, reporting and archiving, of laboratory studies. The Principles may be considered as a set of criteria to be satisfied as a basis for ensuring the quality, reliability and integrity of studies, the reporting of verifiable conclusions, and the traceability of data. Consequently the Principles require institutions to allocate roles and responsibilities in order to improve the operational management of each study, and to focus on those aspects of study execution (planning, monitoring, recording, reporting, archiving) which are of special importance for the reconstructability of the whole study. Since all these aspects are of equal importance for compliance with the Principles of GLP, there cannot be any possibility of using only a choice of requirements and still claiming GLP compliance. No test facility may thus rightfully claim GLP compliance if it has not implemented, and if it does not comply with, the full array of GLP rules.

Reference Handbook of Good laboratory practices. Quality practices for regulated non-clinical research and development. UNDP/World Bank/ WHO – Special program for research and training in tropical disease, Geneva, Switzerland.


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Requirement for test facilities. OECD principals of good laboratory practice for GLP certification. National GLP compliance monitoring authority. Department of Science Technology, India. Green, M.J. (1996). A practical guide to analytical method validation. Analytical Chemistry, 68: 305A-309A. Sivela, S (1988). Good laboratory practices in the dairy industry. Bulletin of the International Dairy Federation; 229: 24-26. Wood R, Nilsson A and Walin, H (1998). Quality in the food analysis laboratory. RSC Food Analysis Monograph. The Royal Society of Chemistry, Cambridge.


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CHEMISTRY OF QUALITY ATTRIBUTES IN HEAT PROCESSED DAIRY PRODUCTS

Dr. (Mrs.) Bimlesh Mann Dairy Chemistry Division NDRI, Karnal-132001

The main milk processing treatments involve separation, homogenization, heating, membrane processing and fermentation. The manufacture of virtually all milk and dairy products involves heat treatment. Such treatment is mainly aimed at: 1. Warranting the safety of consumer. 2. Increase the keeping quality. 3. Establishing specific product properties Milk is a heterogeneous system and each component has its own role in heat processing treatment. The main variable is, of course, heating intensity (i.e., temperature and duration of heating). Many combination of time and temperature may thus be of the same intensity (i.e., cause the same extent of reaction), but the combinations are usually different for different reaction. A proper understanding of these factors and a balance between them is essential for producing products with desirable properties Influence of heat treatment on the constituents of milk: Changes in milk caused by increase in temperature may be reversible or irreversible. Reversible changes include the mutarotation equilibrium of lactose and ionic equilibria, including pH. Numerous irreversible changes caused by heat treatment are as follows: •

•

Gases, including CO2, are removed (if they escape from the heating equipment). Loss of O2 is important for the rate of oxidation reaction during heating and for the growth rate of some bacteria afterward. The loss of gases is reversible, but uptake of air may take a long time. The cream plug phenomenon is evident at 74°C. Various theories have been discussed, but it appears that liberated free fat cements the fat globules when they collide. Homogenisation is recommended to avoid cream plug formation. Fink and Kessler (1985) have shown that free fat leaks out of the globules in cream with 30% fat, unhomogenised as well as homogenised, when it is heated to temperatures between 105 and 135°C. This is believed to be caused by destabilisation of the globule membranes resulting in increased


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permeability, as a result of which the extractable free fat acts as cement between colliding fat globules and produces stable clusters. Above 135°C the proteins deposited on the fat globule membrane form a network which makes the membrane denser and less permeable. Homogenisation downstream of the steriliser is therefore recommended in UHT treatment of products with a high fat content. The composition of the surface layers of the fat globules formed during homogenization or recombination is affected by the intensity of heating before homogenization, mainly because of denaturation serum proteins. This affects some properties of the products. For example, the tendency to form homogenization clusters. Glycerides are hydrolysed and interesterified. Lactones and methyl ketones are formed from the fat.

Fig 1: During denaturation κ-casein attach to β-lacto globulin •

The major protein, casein, is not considered denaturable by heat within normal ranges of pH, salt and protein content. Whey proteins, on the other hand, particularly β-lactoglobulin which makes up about 50% of the whey proteins, are fairly heat sensitive. Denaturation begins at 65°C and is almost completed when whey proteins are heated to 90°C for 5 minutes. Whey protein heat denaturation is an irreversible reaction. The randomly coiled proteins "open up", and β-lactoglobulin in particular is bound to the κ-casein fraction by sulphur bridges. The strongly generalised transformation is shown in figure 1. Blockage of a large proportion of the κ-casein interferes with the renneting ability of the milk, because the rennet used in cheese making assists in splitting the casein micelles at the κ-casein locations. The higher the pasteurisation temperature at constant holding time, the softer the coagulum; this is an undesirable phenomenon in production of semi-hard and hard types of cheese. Milk intended for cheese making should therefore not be pasteurised, or at any rate not at higher temperatures than 72°C for 15 – 20 seconds. In milk intended for cultured milk products (yoghurt, etc.), the whey protein denaturation and interaction with casein obtained at 90 – 95°C for 3 – 5 minutes will contribute to improve quality in the form of reduced syneresis


145

•

•

•

•

•

•

and improved viscosity. Milk heated at 75°C for 20 – 60 seconds will start to smell and taste “cooked”. This is due to release of sulphurous compounds from β-lacto globulin and other sulphur-containing proteins. Most of the serum proteins are denatured and thereby are rendered insoluble. Enzymes can be inactivated by heating. The temperature of inactivation varies according to the type of enzyme. There are some bacteria, Pseudomonas spp, (spp = species) nowadays very often cited among the spoilage flora of both raw cold-stored milk and heat treated milk products, that have extremely heatresistant proteolytic and lipolytic enzymes. Only a fraction of their activity is inhibited by pasteurisation or UHT treatment of the milk. Lactose undergoes changes more readily in milk than in the dry state. At temperatures above 100 °C a reaction takes place between lactose and protein, resulting in a brownish colour. The series of reactions, occurring between amino groups of amino acid residues and aldehyde groups from milk carbohydrates, is called the Maillard reaction or browning reaction. It results in a browning of the product and a change of flavour as well as loss in nutritional value, particularly loss of lysine, one of the essential amino acids. It appears that pasteurised; UHT and sterilised milks can be differentiated by their lactulose content. Lactulose is an epimer of lactose formed in heated milks (Adachi, 1958). Martinez Castro & Olano, 1982, and Geier & Klostermeyer, 1983, showed that pasteurised, UHT and sterilised milks contain different levels of lactulose. The lactulose content thus increases with increased intensity of the heat treatment. Lactose isomerizes and partly degrades to yield, for instance, lactulose and organic acids. Vitamin C is the vitamin most sensitive to heat, especially in the presence of air and certain metals. Pasteurisation in a plate heat exchanger can however, be accomplished with virtually no loss of vitamin C. The other vitamins in milk suffer little or no harm from moderate heating. Of the minerals in milk only the important calcium hydroxyphosphate in the casein micelles is affected by heating. When heated above 75°C the substance loses water and forms insoluble calcium orthophosphate, which impairs the cheese making properties of the milk. The degree of heat treatment must be carefully chosen. The amount of colloidal phosphate increases and the Ca2+ decreases. These changes are reversible, though slowly. Phosphoric acid esters, those of casein in particular are hydrolysed. Phospholipids and some dissolved esters are also split. Consequently the amount of inorganic phosphate increases. Heating milk at first makes it a little whiter, maybe via the amount of colloidal phosphate increases and the Ca2+ decreases. At increasing heating intensity the color becomes brown, due to reactions between lactose and protein occur, Maillard reactions in particular. Viscosity may increase slightly because most of the serum proteins are denatured and there by are rendered insoluble, and much more due to Casein


146

•

•

•

•

micelles become aggregated. Aggregation may eventually lead to coagulation. The latter change especially occurs when concentrated milk is sterilized. Tendency for age thickening and for heat coagulation of concentrated milk may be decreased. Several bacteria can grow faster in heat treated milk because bacterial inhibitors like lactoperoxidase-H2O2-CNS and immunoglobulin are inactivated. Furthermore, heat treatment may lead to formation of stimulants for some bacteria or inhibitors for still other bacteria. All these changes greatly depend in heating intensity. The proneness to auto oxidation is affected in several ways mainly due to formation of free sulfhydryl groups which causes, for instance a drop of the redox potential (Eh), inactivation of enzymes and several changes occur in the fat globule membrane, e.g., in its Cu content. Heating of milk above 70ºC causes a noticeable decrease in the Eh due to liberation of –SH groups from whey protein and loss of O2. Compounds formed by the Maillard reaction between lactose and proteins can also influence the Eh of heated milk, particularly dried milk products. Pasteurization causes some changes in pH due to the loss of CO2 and precipitation of calcium phosphate. Higher heat treatment (above 100 ºC) results in a decrease in pH due to the degradation of lactose to various Organic acids. Pasteurization of milk has little effect on its surface tension although heating milk to sterilization temperatures causes a slight increase in surface tension, resulting from denaturation and coagulation of protein which are then less effective as surfactants. Heat treatment of buffalo milk causes reduction of curd tension.

Heat processed Dairy products and chemical quality attributes: The deteriorative processes that occur in foods after harvesting and during storage and distribution are unavoidable. If food is untreated, microbial deterioration becomes the dominant process affecting safety and quality. Even if the foods are treated to reduce or eliminate microbial contamination, chemical and physical deterioration become the dominant processes in determining storage life time and in altering product quality. Accordingly, if technological strategies are to be devised to retard such deterioration and to minimize the consequent loss of quality, it is crucial to understand the nature of physico-chemical changes (instabilities) in the constituents and the factors that control component degradation. Physico-chemical changes takes place in milk during processing directly related to the colour, flavour and texture of the final dairy products. Ultimately delivering quality dairy foods desired by consumers depends on being able either to modify the instability of major constituents or choose processing and storage conditions that minimize the chemical or physical deterioration. Some of such major changes which act as quality indices are being mentioned below.


147

Nonenzymatic browning One of the most common reactions in milk products is the non enzymatic browning reaction, the Maillard reaction. It can involve reducing sugars and amino groups on the protein, consequent changes in colour and texture of the proteins can occur under abusive storage conditions, because it’s Q-10 (the increase in the rate constant as temperature is raised by 10°C) in 3-4. The thermal processing involved in condensing and drying initiates a Maillard reaction between the reducing sugar and the amino containing molecules of foods. The Maillard reaction, other reactions following from it, continue during storage and eventually result in the development of brown colour, changes in solubility of powdered foods, loss of nutritional value (chiefly lysine availability) and stale flavours. These reactions may limit the shelf life of sterile concentrates and powders. Much of 5 hydroxy- methyl furfural produced by these reactions in sterileconcentrated skim milk occur during thermal processing but that the brown pigment is produced during storage and is protein bound. Commercial non fat powder and infant formulae stored at 30°C to 40°C for one month at aw 0.8 become dark brown and lost 29 and 45% of their available lysine respectively. At aw 0.2 or less the loss was greatly reduced. Available lysine was reduced by 12, 23 and 49% for non-fat dry milk stored at 4, 20 and 37°C at aw 0.75. At water activity 0.44 the loss of available lysine and browning increases. The greater deterioration at aw 0.44 was attributed to the crystallization of lactose and release of moisture that occurred at this aw (La Grange and Hammond, 1995). Sterilization of paneer cubes leads to browning accompanied with cooked flavour affected the organoleptic quality of paneer. Paneer cubes fried prior to sterilization spoiled earlier due to the development of oxidised flavour. Many of the sulphur-containing flavours that are produced during heating capable of further reaction, particularly with carbonyls, and this can cause abatement of the heated flavour during storage and some time the generation of new flavours. Sulphur compounds dominate the flavour produced by milk heat treatment. Reps et al., (1987) showed that autoclaving milk gave rise to glyoxal and methyl glyoxal, presumably through carboxyl amine reaction. These dicarbonyl have shown to react with methionine and cysteine to produce many of the sulphur compounds identified in milk. Reaction of these dicarbonyls with phenylalanine account for many of the aromatic compounds identified in heated milk. Methyl glyoxal can dimerise to 2, 5 dimethyl-4hydroxy3 (2H) furanone which may partly account for the caramelised flavours that are observed. Lactones and methyl ketones released from milk fat by heat treatment also may play a role in heated flavour (Scanlan et al., 1968). The stale flavour resulted primarily from reaction of free amino acids with carbonyl generated in the browning quality of protein foods due to Maillard reaction can occur during storage with minimal change in the nutritive value, it can be avoided


148

by a proper selection of ingredients, time and temperature during thermal processing and storage conditions like aw and temperature. Conversely the nutritional value of the proteins should not be a significant problem as long as the foods are acceptable to the consumer from sensory point of view. Proteolysis Proteolysis means proteolytic changes occurring in foods that have low but discernible enzymatic activity for example protein changes associated with storage in some dairy products (Barnett and Kim, 1998). Cheese manufacture begins with the use of proteolytic enzymes such as rennet to cause milk to coagulate to produce cheese curd. During aging, continued proteolysis contributes to flavour and texture development. For some cheese types residual protease activity can have an adverse effect on quality. For example, the tensile strength of Mozzarella cheese decreases logarithmically with storage time due to protease activity. Paneer is highly susceptible to chemical changes. Proteolysis and lipolysis are two major changes which affect the quality of paneer during storage. UHT processed milk eventually gel upon storage and develop off flavours even through there is no microbial growth. One of the proteases responsible for is plasmin, which probably enters the milk from blood in the forms of its precursor, plasminogen (Walstra and Jenness, 1984). In fresh milk, most of the enzyme is present as the precursor. Increased plasmin activity is observed after UHT treatment and plasminogens decrease with plasmin activity increases upon storage (Manji, 1987). Lipolysis The majority of natural lipids consist of fatty acids attached to glycerol through carboxylic ester bonds. Hydrolysis of the ester bonds catalyzed by acid, alkali, heat, moisture or lipolytic enzymes result in the liberation of per fatty acid. Enzyme may be present naturally in food or in constituents mixed with food; some could be associated with microbial contamination. Temperature, moisture and pH are among the factors control lipase activity. Off favours resulting from hydrolytic rancidity are more likely to occur in fat containing relatively short chain fatty acid i.e. C 4-10). The potential for lipolysis in milk however is minimized due to the structure of the milk emulsion, which limits physical contact between triacyl glycerol substance residing in fat glycerols and the lipase enzyme in the skim milk. Agitation during processing the native milk structure and promote enzyme substrate interaction. Although heat inactivates the lipolytic micro organisms, the lipases produced by them can survive normal pasteurization temperatures. Many typical flavours are produced where short chain fatty acids are hydrolysed by natural milk or microbial lipolytic enzymes (Nawar, 1998). Khoa has a low keeping quality at room temperature and develops rancid flavour due to hydrolysis of fat by lipase action. Due to the vigorous agitation of milk at high temperature, the fat globules are appreciably sub-divided. Considerable free fat is also Sensory and Related Techniques for Evaluation of Dairy Foods

149

produced due to the rupturing of the fat globule membrane by the vigorous scraping action of the stirrer. The vigorous agitation of hot milk has an appreciable homogenising action so that when the stage of coagulation is reached all the fat globules are entrained in the coagulum. Almost half of the globular fat is released as free fat. The extent of which depend upon fat contents of milk and manufacturing process. Oxidation Lipid oxidation is of paramount important to food quality. It may lead to the development of rancid off flavours, cause change in colour texture, reduce shelf life and/or impair nutritional quality. However a limited degree of lipid oxidation is sometimes desirable, as in the formulation of typical flavours and aromas that are associated with cheese and fried food. Lipid oxidation proceeds via a typical self propagating free radical mechanism where oxygen attaches occurs mainly at positions adjacent to the double bounds. The breakdown of hydro peroxides leading to the formation of volatile and non volatile product may also be catalysed by enzyme (i.e. hydroperoxidase). Obviously due to the greater specificity in enzyme-catalysed formation and decomposition of fatty acid; hydro peroxide and other specific oxidation and products are encountered. The various factors which influence the lipid oxidation are free fatty acids, the fatty acids positions in triacylglycerols, oxygen concentration, temperature, water content, physical conditions, prooxidants and antioxidants. Although milk fat contains relatively low concentrations of poly unsaturated fatty acid (about 3%). These play the primary role in the development of oxidized flavours-vinyl ketones such as 1-octen-3 one or octa-1 cis 5 diene- 3 one play a dominant role in the flavour of oxidized milk. The vinyl ketones themselves give milk a metallic flavour but when blended with an aldehyde give a typical oxidized flavour. Oxidation in dairy products also can be initiated by exposure to light (Korycka and Richardson, 1978; 1979 and 1980). But the irradiated flavours produced in this way are significantly different from those produced by metalcatalyzed oxidation. Riboflavin is the primary pigment involved in irradiated flavour. Light activated riboflavin is reduced by molecules such as methionine, producing sulphur compounds typical of irradiated flavour. The reduced riboflavin can react with oxygen can be quite rapid and lead to noticeable flavour in a few minutes to a few hours of exposure, depending on the intensity and wave length of the light. Typically ghee possesses a pleasant buttery, light caramelized sweet acidic aroma. Flavour development and its profile in ghee is quite complex.According to Bindal and Jain (1973), the flavour of ghee developed through the possible interaction during heating process among a protein (probably casein degradation product), a reducing sugar (lactose) and minerals. At the temperature of clarification employed during the process of manufacture, the carbonyl content increases. On prolong storage of ghee the off flavour has been found in ghee samples with three fold increase in Sensory and Related Techniques for Evaluation of Dairy Foods

150

total carbonyls. The level of lactones increased with increase in clarifying temperature. The deterioration due to oxidative rancidity of ghee depends on degree of unsaturation in fat, availability of oxygen, heat, light, moisture content, free fatty acids, oxidation catalyst and antioxidants. Heating milk and cream to 75°c - 85°c develops a cooked flavour due to release of –SH group which delays oxidation significantly. Addition of heat dried skim milk act as an antioxidant in butter or cream. Butter, cream, whole milk powder and even milk may develop a fishy flavour due to certain amines that possesses fishy flavour and odours. Lecithin is the only source of organic nitrogen in the amine form because of the presence of choline. Choline is decomposed to trimethylamine. Production of fishy flavour is related to conditions favourable for hydrolysis and oxidation of lecithin. Irradiated flavour often is the most common defect in market milk because of the wide spread sale of milk is translucent polyethylene in well lightened place. In powdered milk especially powdered whole milk, flavour deterioration can occur through fat oxidation. This can be affected by the amount of free fat on the particle surface, the water content of the powder, the sort of packaging used, storage temperature, exposure to light and the addition of antioxidants. The oxidation of cholesterol in spray dried powders may be a health concern (Hall and Linguert, 1984; and Clevelard and Harris, 1987). A number precautionary measures based mainly on the various aspects considered above can be recommended for prolonged shelf-life that is limited by oxidation and for minimizing undesirable changes in the quality of edible oil and fat containing foods:

• • • • • • • •

Select high quality raw material (e.g. seeds with minimum damage, oils with low FFA content and high resistance to oxidation. Use high quality food ingredient (e.g. milk, nuts, spices) Use techniques that reduce substrate catalyst interaction (i.e. avoid cell disruption, contact with enzyme). Minimize contact with oxygen, light and/or trace metals. Minimize exposure to elevated temperature. Use packaging that provides a reasonable gas barrier during storage and distribution. Minimize surface area in contact with air. Design and maintain proper storage tanks and pipe line (e.g. stainless steel, if possible; glass lining, free of copper and copper alloys, frequent cleaning, minimal head space, lowest practical temperatures, protection for contamination with micro organisms and regular inspection)


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• Use appropriate antioxidants. Beside non-enzymatic browning and lipid oxidation there are other physicochemical changes take places during storage of food products which affect the texture, colour, flavour and overall acceptability of foods. Viscosity, gelation and sedimentation The factors limiting the shelf life and acceptability of liquid products are change in viscosity, precipitation and gelation. These reactions are seen typically in concentrated, sterile products. The traditional process for in-can sterilization of milks, supplemented with, judicious addition of phosphates, citrates and gums, typically produces products that are reasonably stable for over a year. However holding the concentrated product in refrigerated storage before canning, results in more rapid gelation (Halwalkar et al., 1983). When ultrahigh temperature processing and aseptic packaging is used, precipitation and gelation are a more common problem. The cause of those changes is not definitely established but may cause by incomplete destruction of the milk protease plasmin which in fairly heat stable. In any event the storage of UHT-sterilized milk is often accompanied by proteolysis (Harwalker and Vreeman, 1978); Mckenna and Singh 1991), but leads to the joining of casein micelles by thin, hair like linkages and gelation (Zadow and Hardham, 1981; Koning et al., 1994). Gelation often in proceeded by precipitation and an increase in viscosity (Newstead et al., 1978; Snoren et al., 1984). These changes are affected by extent of concentration, season and lactation of milk production, extent of heat treatment, temperature of storage, pH and addition of polyphosphate and other ions.

Sedimentation of protein in UHT milk occurred if the pH was less than 6.55 (Zadow and Hardham, 1981). Sequestering calcium reduced sedimentation. Harwalker and Vreeman 1978 found that the viscosity of UHT treated skim milk was much increased in 9 weeks, while samples with added phosphate lasted 12 weeks. Both of these samples gelled by 18 weeks. Samples with added polyphosphate showed no increase in viscosity on gelation at 18 weeks. Mckenna and Singh (1991) reported that UHT processed reconstituted concentrated milk containing 0.075% Hexametaphosphate did not gel or become viscous for 6 months at 22°C. To achieve this shelf life at 30°C 0.075 to 0.15% Hexametaphosphate was needed. Crystallization of lactose The major detriment to the shelf life of dry milk products in moisture, to much moisture in processed dry milk and or moisture from the atmosphere getting into the product during storage. The dry lactose in milk powder is very hydroscopic and readily picks up moisture from the atmosphere. Amorphous lactose is formed when a solution (e.g. milk) is dried rapidly as in a spray drier or frozen. If the water content of amorphous lactose is low, say 3% crystallization may be postponed almost indefinitely; nucleation rate is negligible because of the


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extremely high viscosity of the solution. The product is however very hydroscopic, and when moisture content arises to about 8%, lactose hydrate starts to crystallize. But when crystallization of lactose caused by moisture uptake occurs in milk or whey powder, the result in caking, powder particles and concentrated together by crystalline lactose, forming large and strong lumps. (Walstra and Jenness, 1984). Controlling the moisture of milk/powder between 3.5 and 3.9% and maintaining this moisture level within package will assume a shelf life of at least one year from the date of processing and packaging (Laarange and Haurmond 1993). Lactose crystals rupture fat globule membrane and thus free fat amount is considerably increased and it leads to an oily layer formation, greasiness etc. after reconstitution and faster oxidation. Thus crystallisation of lactose affects the dispersibility, baking and sensory quality of the products. In roller dried powder about 90% of fat exists as free fat whereas in spray dried milk powder, most of the fat exists as globule with membrane intact. In spray dried milk powder, the action is similar to homogenization, fat globules subdivide, otherwise remain distributed throughout the particles in globular form. During spray, air is incorporated so fat tends to surround the air particles. The free fat is milk powders leads to oxidation. High moisture, excessive absorption of moisture by lactose resulting in lactose crystallisation leads to lumping/ caking of powder. High moisture powder is more prone to insolubility due to denaturation of protein. More moisture also favours browning reaction, auto oxidant and hydrolytic rancidity. During storage and distribution, dairy foods are exposed to a wide range of environmental conditions. Environmental factors such as temperature humidity, oxygen and light can trigger several reaction mechanisms that may lead to food degradation. As a consequence, food may be altered to such an extent that they are either rejected by consumer, or they may become harmful to the person consuming them. It is, therefore, imperative that a good understanding of different physicochemical reactions that cause deterioration is gained prior to developing specific methods for the evaluation, monitoring and predicting the quality of these dairy products.

References: Barnett R.E. and Kim. H.J. (1998) Protein instability. In Food storage stability, CRC Press, chapter 3, pp 75-87. Bindal,MP and Jain,MK(1973) Indian J.Ani. Sci.43(10),918-24 Cleveland H.Z. and Harris, N.D. (1987) J. Food Protection 50: 867-871. Fink A. and H.G. Kessler (1985) Milchwissenschaft 40, 6-7. Hall G. and Lingnert H. (1984) J. Food Quality 7:131-151.


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Harwalkar, V.R.; Backett. D.C. ; McKeller, R.C.. Emmons, D.B. and Doyle G.E. (1983) Age thickening and gelation of sterilized evaporated milk. J. Dairy Sci., 66 : 735-742. Harwalkar, V.R. and Vreeman H.D. (1978) Neth Milk Dairy J. 32 204-216. Harwalkar, V.R. and Vreeman, H.D. (1978) Neth. Milk Dairy J. 32: 204-216. Korycka, Dahl. M. and Richardson, J. (1978) J.Dairy Sci., 61: 400-407. Korycka, Dahl. M. and Richardson, J. (1979J. D. Sci. 62 : 182-183. Korycka Dahl M and Richsrdson, J. (1980J. Dairy Sci., 63 : 1181-1198. La Grange, W.S. and Hammond, E.G. (1995) The Shelf life of Dairy Products. In Shelf life Studies of Foods and Beverages, Elsevier Science publishers Chapter 1, pp 1-20. Mauji, B.S. (1987) Ph.D Dissertation University for Guelph Ont, cited from Food Storage Stability, Taub and Paul Singh, Eds. CRC Press, Chapter 3, pp 75-87. Mckenna, A.B. and Singh H. (1991) Int. J. Food Sci. and Technol., 26: 27-28. Newstead, D.F., Baldwin, A.j. and Hughes, I.R. (1978) New Zealand Dairy Sci. and Technol., 13: 65-70. Nawar, W.W. (1998) Biochemical Processes: Lipid instability, In Food storage stability, Taub and Paul Singh Ed, CRC Press, Chapter 4, pp 89-103. Repg, A., Hammond, E.G., Glatz, B.A. (1987)

J. Dairy Sci. 70: 559-562.

Scaulan, R.A., Lindsay, R.C., Libbey, L.M. and Day E.A. (1968) J. Dairy Sci., 51: 1001-1005. Szczesniak, A.S. (1998) Effect of storage on texture. In Food storage stability, Taub and Paul Singh Eds., CRC Press, Chapter 4, pp 89-103. Walstra, P. and Jennes, R. (1984) Enzymes. In Dairy Chemistry and Physics, Wiley, New York, Chapter 7, pp-133. Zadow, J.G. and Hardham, J.F. (1981) Aust. J. Dairy Techol., 36: 30-33.


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DETERMINATION OF SORPTION ISOTHERMS AND GENERATION OF SORPTION DATA R. R. B. Singh Division of Dairy Technology National Dairy Research Institute, Karnal

Introduction Water is an integral part of all food systems. It determines behavior of food products during many processing operations and significantly affects the quality of food. An understanding of the state of water in foods that is characterized by water activity aw is therefore essential to control and optimize various physical, chemical and microbial changes in food systems. Determination of sorption isotherms thus, has several applications in food science. In mixing operations and development of a new product formulation, sorption isotherm data of each component will help to predict transfer of moisture from one product to another, which is essential for controlling the deterioration of the final product. Determination of enthalpy of sorption and desorption of water at two different temperatures gives an indication of binding strength of water molecules to the solid and has definite bearing on the energy balance during drying and freezing operations. Sorption isotherm is also important in packaging operations as the knowledge of initial and maximum allowable moisture content and aw along with the surface and permeability of the packaging material will help in determining shelf life of the packaged foods under varying conditions of storage. Methods for determination of sorption isotherms Methods that have been developed for determining sorption isotherms can be broadly classified under two heads: A. Gravimetric methods; B. Manometric and Hygrometric methods. Although several innovations have been tried in both the group of methods of measurement to improve the rapidity and accuracy of measurement, the following gravimetric method has been recommended by the cost projects 90 and 90-bis on physical properties of foodstuffs. (COST = Co-operation in the field of Scientific and Technical Research in Europe) and remains by far the most widely used and reliable method of determining sorption isotherms. Principle of measurement The principle underlying the method of measurement is that food product is exposed to a controlled environment of relative humidity at defined temperature


155

condition. The weight of the sample is monitored at definite intervals till a time there is no change in weight as the food attains equilibrium with the environment. Such determinations at several relative humidity (RH) conditions will yield a sorption isotherm. 2.2

Design of the sorption apparatus The equipment which has been recommended consists of a simple arrangement comprising of glass jars as sorbostat with vapour tight lids. Sorbed source in sufficient quantity is placed in the jar to maintain large sorbate to sample ratio. The substance is placed in small weighing bottles standing on trivets directly above the sorbate source. The jars are then placed in thermostatically controlled incubators or water baths maintained at predetermined temperatures.

Fig. 1. Sorption apparatus 1. Sorption container; 3. Petridish on trivets;

2. Weighing bottle with ground in stopper; 4. Saturated salt solution

2.3

Sorbate sources for creating constant ERH

2.3.1

Sulphuric acid solutions of varying concentrations: Depending on the concentration, sulphuric acid solutions will have varying water vapour pressure and the ERH in the headspace will accordingly change. The major limitations of using H2SO4, however, remains change in the concentration due to loss or gain of moisture thereby altering the ERH conditions. The following Table gives aw of sulfuric acid solutions at different temperature.


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Table 1.

Water activity of sulfuric acid solutions at different concentrations and temperatures

H2SO4 Density at 25oC (%) (g/cm3)

Temperature (oC) 5

10

20

25

30

40

50

5

1.0300

0.9803

0.9804

0.9806

0.9807

0.9808

0.9811

0.9814

10

1.0640

0.9554

0.9555

0.9558

0.9560

0.9562

0.9565

0.9570

15

1.0994

0.9227

0.9230

0.9237

0.9241

0.9245

0.9253

0.9261

20

1.1365

0.8771

0.8779

0.8796

0.8805

0.8814

0.8831

0.8848

25

1.1750

0.8165

0.8183

0.8218

0.8235

0.8252

0.8285

0.8317

30

1.2150

0.7396

0.7429

0.7491

0.7521

0.7549

0.7604

0.7655

35

1.2563

0.6464

0.6514

0.6607

0.6651

0.6693

0.6773

0.6846

40

1.2991

0.5417

0.5480

0.5599

0.5656

0.5711

0.5816

0.5914

45

1.3437

0.4319

0.4389

0.4524

0.4589

0.4653

0.4775

0.4891

50

1.3911

0.3238

0.3307

0.3442

0.3509

0.3574

0.3702

0.3827

55

1.4412

0.2255

0.2317

0.2440

0.2502

0.2563

0.2685

0.2807

60

1.4940

0.1420

0.1471

0.1573

0.1625

0.1677

0.1781

0.1887

65

1.5490

0.0785

0.0821

0.0895

0.0933

0.0972

0.1052

0.1135

70

1.6059

0.0355

0.0377

0.0422

0.0445

0.0470

0.0521

0.0575

75

1.6644

0.0131

0.0142

0.0165

0.0177

0.0190

0.0218

0.0249

80 1.7221 0.0035 0.0039 Source: Rao and Rizvi, 1986

0.0048

0.0053

0.0059

0.0071

0.0085

2.3.2 Glycerol solutions: Glycerol solutions of varying concentrations (adjusted with water) can also be used for creating constant ERH conditions. The difficulty in using glycerol solutions, however, arises from the fact that glycerol can volatilise and absorb into the foods thereby causing error. Un like H2SO4, it is non-corrosive but gets diluted or concentrated during sorption due to loss or gain of moisture from the sample. Table 2 below gives aw of glycerol solutions.


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Table 2. Water activity of glycerol solutions at 20oC Concentration Refractive index Water activity (kg/L) 1.3463 0.98 1.3560 0.96 0.2315 1.3602 0.95 0.3789 1.3773 0.90 0.4973 1.3905 0.85 0.5923 1.4015 0.80 0.6751 1.4109 0.75 0.7474 1.4191 0.70 0.8139 1.4264 0.65 0.8739 1.4329 0.60 0.9285 1.4387 0.55 0.9760 1.4440 0.50 1.4529 0.40 Source: Rao and Rizvi, 1986 2.3.3 Salt slurries: Saturated slurries of various inorganic and organic salts produce constant ERH in the headspace of sorption container. The ERH decreases with increasing temperature due to increased solubility of salts with increasing temperatures. The Table 3 below gives aw of different salt slurries at varying temperatures. Table 3. Water activities of different salt slurries at various temperatures Salt

5 Lithium chloride 0.113 Potassium acetate Magnesium chloride 0.336 Potassium carbonate 0.431 Magnesium nitrate 0.589 Potassium iodide 0.733 Sodium chloride 0.757 Ammonium sulfate 0.824 Potassium chloride 0.877 Potassium nitrate 0.963 Potassium sulfate 0.985 Source: Rao and Rizvi, 1986

10 0.113 0.234 0.335 0.431 0.574 0.721 0.757 0.821 0.868 0.960 0.982

Temperatures (oC) 20 25 30 0.113 0.113 0.113 0.231 0.225 0.216 0.331 0.328 0.324 0.432 0.432 0.432 0.544 0.529 0.514 0.699 0.689 0.679 0.755 0.753 0.751 0.813 0.810 0.806 0.851 0.843 0.836 0.946 0.936 0.923 0.976 0.970 0.970


40 0.112 0.316 0.484 0.661 0.747 0.799 0.823 0.891 0.964

50 0.111 0.305 0.454 0.645 0.744 0.792 0.812 0.848 0.958

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Preparation of salt slurries: The Table 4 gives the proportion of different salts to water for preparing saturated slurries. Table 4. Preparation of recommended saturated salt Solutions at 25oC Salt

RH (%)

Salt (g)

Water (ml)

LiCl

11.15

150

85

CH3COOK

22.60

200

65

MgCl2

32.73

200

25

K2CO3

43.80

200

90

Mg(NO3)2

52.86

200

30

NaBr

57.70

200

80

SrCl2

70.83

200

50

NaCl

75.32

200

60

KCl

84.32

200

80

BaCl2 90.26 250 Source: Spiess and Wolf, 1987

70

The following equations (Table) can be used for predicting aw of known salt slurries at any temperature. Table 5. Regression equations of water activity of selected salt solutions at different temperatures Salt

Equation

R2

LiCl

Ln aw=(500.95/T)-3.85

0.976

KC2H3O2

Ln aw=(861.39/T)-4.33

0.965

MgCl2

Ln aw=(303.35/T)-2.13

0.995

K2CO3

Ln aw=(145.0/T)-1.3

0.967

MgNO3

Ln aw=(356.6/T)-1.82

0.987

NaNO2

Ln aw=(435.96/T)-1.88

0.974

NaCl

Ln aw=(228.92/T)-1.04

0.961

KCl

Ln aw=(367.58/T)-1.39

0.967

Temperature ‘T’ in Kelvin Source: Rao and Rizvi, 1986


159

While preparing salt slurries, the following care must be taken to improve precision of measurement: • • • • • •

• • •

Only AR grade salts should be used. Salt crystals in excess should be present at the bottom. Before the samples are placed, the containers with slurries should be maintained at required temperatures for 3-4 days for allowing equilibration. The ratio of slurry surface to sample surface should preferably be >10:1. The ratio of air volume to sample volume should be 20:1 The salt slurries should be occasionally stirred to prevent change in concentrations of top liquid layer due to loss or gain of moisture from the sample. Precautions: Some salts are caustic: potassium dichromate, potassium chloride Some salts are highly toxic: lithium chloride, sodium nitrite Alkaline solutions such as K2CO3 absorb large amounts of CO2 with time thereby decreasing aw significantly Standardization of sorption apparatus with reference materials The recommended material for this purpose is microcrystalline cellulose (MCC). This material is very stable against changes in the sorption behaviour and can be used even after 2 to 3 repeated adsorption and desoption cycles. It does not exhibit hysteresis between adsorption and desorption and require very short periods for reaching equilibrium. Preparation of samples: The test substrate should be prepared in a way that ensures homogeneity so that sample drawn for sorption studies is representative of the bulk. Sample size should normally be 1 gm and at least three replications should be used for minimizing error in the study. For adsorption isotherms, samples should be vacuum dried preferably at 30°C for 30-40 hrs. followed by freeze drying and desiccant drying to reduce the moisture level to a level lower than the corresponding lowest water activity of the saturated salt being used. Once the samples have been weighed accurately and placed in the sorption jar, weighing should follow at regular intervals till the sample reaches equilibrium and the change in weight in three subsequent weighing does not change by more than 2 mg per gm of sample. Types of moisture sorption curves The sorption isotherms are obtained by drawing a plot of moisture (g/100 g of sample, db) vs water activity. The isotherms thus obtained could be classified according to the following five general types.


160

Moisture

Type II

Type I (Langmuir)

(sigmoid)

a

Type IV Type III

Type V

Fig. 2. The five types of van der Walls adsorption isotherms Isotherm models Over the years, a large number of isotherm models have been prepared and tested for food materials. These can be categorized as two, three or four parameter models. Some of the most commonly used models are presented hereunder: Two parameter models

1. Oswin

⎧ aw ⎫ W = a⎨ ⎬ ⎩ (1 − a w ) ⎭

2. Caurie

ln

3. Halsey

4.BET Equation

b

1 1 2C 1 − a w = ln + ln W C.W0 W0 aw

aw = e

⎡ −a ⎤ ⎢ b⎥ ⎣W ⎦

W=

W0 B.aw (1 − aw)[1 + ( B − 1)aw]


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Three parameter models

1. GAB

W = W0

2. Modified Mizrahi

W=

Gka w (1 − k a w )[1 − ka w + Gka w ]

a + a w (c.a w + b) aw − 1

Where, W = Equilibrium moisture content, g/100 g solids W0 = Moisture content equivalent to the monolayer aw = water activity a, b = Constants B = Constant C = Density of sorbed water G = Guggenheim constant k = Correction factor for properties of multiplayer molecules with respect to the bulk liquid Of these, GAB model has been found to be most appropriate for describing sorption behaviour of food systems over a wide range of water activity. Both BET (application range aw=0.05-0.45) and GAB equations can be used for obtaining monolayer moisture that is critical for quality and shelf life of foods Effect of temperature on water activity

Knowledge of the temperature dependence of sorption phenomena provides valuable information about the changes related to the energetic of the system. The shift in water activity as a function of change in temperature at constant moisture constant is due to the change in water binding, dissociation of water or increase in solubility of solute in water. At constant water activity, most of the foods hold less water at higher temperature. The constant in moisture sorption isotherm equations, which represents either temperature or a function of temperature, is used to calculate the temperature dependence of water activity. The clausius-clapeyron equation is often used to predict aw at any temperature if the isosteric heat and aw values at one temperature are known. The equation for water vapour in terms of isosteric heat (Qst) is given by: a w1 Q st ⎡ 1 1⎤ = ⎢ − ⎥ a w2 R ⎣ T1 T2 ⎦ Where Qst is net isosteric heat of sorption or excess binding energy for the removal of water also called excess heat of sorption. In


162

4600

4100

3600

3100

2600

2100

1600

1100

600 10

20

30

40

50

60

70

80

90

100

M oi st ur e c ont e nt ( % db)

Figure 3. Typical diagram showing net isosteric heat of sorption Hysteresis in adsorption–desorption isotherms

When adsorption and desorption isotherms for the same food material are plotted on the same graph, usually the desorption isotherm lies above the adsorption isotherm and sorption hysteresis loop is formed. Moisture sorption hysteresis has both theoretical and practical implications. The theoretical implications include considerations of the irreversibility of the sorption process and also the question of validity of thermodynamic functions derived therefrom. The practical implications refer to the response of the effects of hysteresis on chemical and microbiological deterioration in processed foods intended for prolonged storage. The hysteresis property of foods is generally affected by the composition, temperature, storage time, drying temperature, and number of successive adsorption and desorption cycles. Several theories have been proposed to explain hysteresis phenomenon in foods. A typical diagram showing hysteresis in sorption isotherm is given below:

Moistur

Desorption Adsorption

Water activity

Figure 4. Typical diagram showing hysteresis phenomenon References:

Kapsalis, J.G. (1981) Moisture sorption hysteresis. In : water activity: influences on food quality (eds. L. B. Rockland and G. F. Stewart), Academic Press. Inc., New York, USA, pp. 143.


163

Rizvi, S.S. H. (1986) Thermodynamic properties of foods in dehydration. In : Engineering properties of foods (eds. M. A. Rao and S. S. H. Rizvi), Marcel Dekker, Inc., New York, USA, pp. 133 Spiess, W.E.L. and Wolf, W. (1978). Critical evaluation of methods to determine moisture sorption isotherms . In: Water activity: Theory and applications to foods (eds. L.B. Rockland and L.R. Beuchat.), Marcel Dekker, Inc., New York, USA, pp. 215. Wolf, W., Spiess, W.E.L. and Jung, G. (1985) Standardization of isotherm measurement (COST- Project 90 and 90-bis). In: Properties of water in foods (eds. D. Simatos and J. L. Multon), Martin Nijhoff Publishers, Dordrecht, The Netherlands, pp. 661.


164

BIOSENSOR IN CHEMICAL QUALITY ASSESSMENT OF DAIRY AND FOOD PRODUCTS

Rajan Sharma

Sr. Scientist, Dairy Chemistry Division, NDRI, Karnal A biosensor is a device incorporating a biologically derived sensing element (e.g. enzyme, antibodies, microorganisms or deoxyribose nucleic acid –DNA) either integrated with or in intimate contact with a physicochemical transducer (e.g. electrochemical, optical, thermoelectric or piezoelectric). The usual aim is to produce a continuous or semi-continuous digital electronic signal which is proportional to a specific chemical or group of chemicals. Devices may be configured as fixed or portable instruments giving qualitative or quantitative information. The modern concept of a biosensor owes much to the ideas of Clark and Lyons (1962). They proposed that enzyme could be immobilized at electrochemical detectors to form ‘enzyme electrode’ which would expand the analyte range of the base sensor. The first biosensor described in literature (Clark and Lyons, 1962; Updike and Hicks, 1967) was based on the combination of glucose oxidase with electrochemical determination of O2 and H2O2. Since then, this principal has been extended to the development of sensors for other analytes using the electroactivity of not only H2O2 and O2 but also NADH and other compounds, so called mediators, for electron transfer from enzyme to the electrode. The key part of a biosensor is the transducer which makes use of a physical change accompanying the reaction. This may be 1. the heat output (or absorbed) by the reaction (calorimetric biosensors), 2. changes in the distribution of charges causing an electrical potential to be produced (potentiometric biosensors), 3. movement of electrons produced in a redox reaction (amperometric biosensors), 4. light output during the reaction or a light absorbance difference between the reactants and products (optical biosensors), or 5. effects due to the mass of the reactants or products (piezo-electric biosensors). A comprehensive list of types of transducers, their characterization and applications is given in Table 1. There are three so-called 'generations' of biosensors; First generation biosensors where the normal product of the reaction diffuses to the transducer and causes the Sensory and Related Techniques for Evaluation of Dairy Foods

165

electrical response, second generation biosensors which involve specific 'mediators' between the reaction and the transducer in order to generate improved response, and third generation biosensors where the reaction itself causes the response and no product or mediator diffusion is directly involved. The electrical signal from the transducer is often low and superimposed upon a relatively high and noisy (i.e. containing a high frequency signal component of an apparently random nature, due to electrical interference or generated within the electronic components of the transducer) baseline. The signal processing normally involves subtracting a 'reference' baseline signal, derived from a similar transducer without any biocatalytic membrane, from the sample signal, amplifying the resultant signal difference and electronically filtering (smoothing) out the unwanted signal noise. The relatively slow nature of the biosensor response considerably eases the problem of electrical noise filtration. The analogue signal produced at this stage may be output directly but is usually converted to a digital signal and passed to a microprocessor stage where the data is processed, converted to concentration units and output to a display device or data store. Table 1. Types of transducers, their characteristics and application

Transducer

Advantages

Disadvantages

Application

Ion-selective electrode(ISE)

Simple, reliable, easy to transport.

Sluggish response, requires a stable reference electrode, susceptible to electronic noise.

Amino acids, carbohydrates, alcohols and inorganic ions

Amperometric

Simple, extensive variety of redox reaction for construction of the biosensors, facility for miniaturization

Low sensitivity, multiple membranes or enzyme can be necessary for selectivity and adequate sensitivity.

Glucose, galactose, lactate, sucrose, aspartame, acetic acid , glycerides, biological oxygen demand, cadaverine, histamine, etc

FET

Low cost, mass production, stable output, requires very small amount of biological material, monitors several analytes simultaneously.

Temperature sensitive, fabrication of different layer on the gate has not been perfected.

Carbohydrates, carboxylic acids, alcohols and herbicide.

Optical

Remote sensing, low cost, miniaturizable, multiple modes: absorbance, reflectance, fluorescence, extensive electromagnetic range can be used

Interference from ambient light, requires high-energy sources, only applicable to a narrow concentration range, miniaturization can affect the magnitude of the signal.

Carbohydrates, alcohols, pesticide, monitoring process, bacteria and other


166

Thermal

Versatility, free from optical interference such as color and turbidity.

No selectivity with the exception of when used in arrangement.

Carbohydrates, sucrose, alcohols, lipids, amines.

Piezoelectric

Fast response, simple, stable output, low cost of readout device, no special sample handling, good for gas analysis, possible to arrays sensors.

Low sensitivity in liquid, interference due to non specific binding.

Carbohydrates, vitamins, pathogenic microorganisms (e.g. E. coli, Salmonella, Listeria, Enterobacter), contaminants (e.g antibiotics, fungicides, pesticides), toxic recognition as bacterial toxins.

Biosensor technology and food analysis

The control of food quality and freshness is of growing interest for both consumer and food industry. In the food industry, the quality of a product is evaluated through periodic chemical and microbiological analysis. These procedures conventionally use techniques such as chromatography, spectrophotometry, elctrophoresis, titration and others. These methods do not allow an easily continuous monitoring, because they are expensive, slow, need well trained operators and in some cases require steps of extraction or sample pre-treatment thus increasing the time of analysis. The food and drink industries need rapid and affordable methods to determine compounds that have not previously been monitored and to replace existing ones. An alternative to ease the analysis in routine industrial products is the biosensor development. These devices represent a promising tool for food analysis due to the possibility to fulfill some demand that the classic methods of analysis do not attain. Original characteristic turns the biosensor technology into a possible methodology to be applied in real samples. Some advantages as high selectivity and specificity, relative low cost of construction and storage, potential for miniaturization, facility of automation. simple and portable equipment construction for a fast analysis and monitoring in platforms of raw material reception, quality control laboratories or some stage during the food processing. The development of biosensors is described in several fields; the majority restricted to other areas of application, as clinical, environmental, agriculture and biotechnology. Developments involving the use of this type of sensor could be employed in foods, especially applied to the determination of the composition, degree of contamination of raw materials and processed foods, and for the on line control of the fermentation process. The food industry has a very set of constrains compared with, for example, the pharmaceutical industry or medical diagnostics. It is important to consider both the limitations and benefits when selecting the target analyte and medium


167

Some of the drawbacks include -

-

-

-

The range of potential applications is enormous. Each product has its own analytical requirements. However, the market for an individual sensor is small compared to, for example, a glucose sensor for use by diabetics. Most biosensor research has been aimed at the medical diagnostics field, where the extreme specificity of a biosensor targeting one selected analyte is extremely advantageous. This is not always applicable to food industry requirement where, for example, a particular taste or smell may be a control parameter. Multisensors would be preferable in many instances due to the complexity of food process control requirement. Most existing processes have been fine-tuned over many years. Often, little process control is required due to the experience of operating the process over such a long period. The biosensor must provide an increase in productivity or quality of the product to be viable. This is not always possible. The technology available must be low cost, simple to use and above all, reliable. Long term stability, drift and calibration are problems which often prevent the introduction of biosensors to industrial processes.

There are also some factors which make the introduction of biosensors in the food industry more feasible: -

-

-

-

Experiment miniaturization is not usually required. This has implications on the fabrication process and on the size of the signal. Destructive or by-pass sampling techniques are usually tolerable. This may facilitate the use of techniques such as flow-injection analysis with biosensor detection. A great deal of work has been carried out in the medical diagnostics industry. Some of the lessons learned in this field may be transferable to food industry requirements. It may not be necessary to provide an instant or continuous measurement. An improvement from days to hours or minutes may be considered sufficiently beneficial. The influence of consumers and regulatory bodies may encourage the use of advanced technolologies such as biosensors.

Table 2 presents some of the important food biosensors, described during last 10 years in the literature. Most of the biosensors described in the literature for food analysis are electrochemical type based on amperometry. The table starts with glucose and other carbohydrates and end with complex parameters such as contaminants and additives compounds. As most works cited are prototypes, they are not fully optimized for a defined application in real samples. Some applications are synthetic


168

samples and can be applied in food samples. Some biosensors listed in the table are used to determine more than one analyte. These are either suitable for determining more than one substrate or are used in combination for simultaneous measurements. Table 2. Applications of biosensors in food analysis Analyte

Application

Biocomponent

Transducer

Detection range

Reference

Glucose

Soft drinks, Glucose juices and oxidase milk

Amperometric

50-500 mM

8, 36

Glucose

Juices Honey

Amperometric

0.5-10 mM

11

4.44 g/10 g (lactose)

18

250-4000 mg/L

19

0.03-15 mm (glucose)

22

Glucose and Milk lactose

Glucose and Yoghurt galactose milk

Glucose, Wine fructose, ethanol, Llactate, Lmalate and sulfite (simultaneou s)

& Glucose oxidase

Glucose Amperometric oxidase, βgalactosidase & mutarotase and Glucose oxidase, galactose oxidase peroxidase

Amperometric

&

Glucose Amperometric oxidase, Dfructose dehydrogenase, alcohol dehydrogenase, L-lactate dehydrogenase, L-malate dehydrogenase, sulfite oxidase & diaphorase

0.01-10 mM (fructose) 0.014-4 mM (ethanol) 0.011-1.5 mM (L-lactate) 0.015-1.5 mM (L-malate) 0.01-0.1 mM (sulfite)

Glucose

Beverages

Glucose oxidase

Glucose

Fruit juice and Glucose cola drinks oxidase

Optical

0.06-30 mmol/L

38

Thermal

0.2-30 mM

27


169

Analyte

Application

Biocomponent

Transducer

Detection range

Reference

Fructose

Honey

D-Fructose dehydrogenase

Amperometric

8.6 µm

9

L-amino acids

Milk and fruit D-amino juices oxidase

0.47-2.5 mM

29

L-glutamate

Soy sauce

L-Gultamate oxidase

Amperometric