FOOD 3007 and FOOD 7012 SENSORY ...

FOOD 3007 and FOOD 7012 SENSORY EVALUATION MANUAL

Associate Professor Richard Mason The University of Queensland and Stephen Nottingham

Sensory Evaluation ACKNOWLEDGEMENTS These notes form the basis of a practical workshop presented for personnel at Naresuan University, Phitsanulok, Thailand in July, 2002. We would like to thank Michael O’Mahony for his permission to include copies of the statistical tables from his book “Sensory Evaluation of Food: Statistical Methods and Procedures” and material supplied by the Centre for Food Technology, DPI, Brisbane.

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R L Mason and S M Nottingham

Sensory Evaluation TABLE OF CONTENTS ACKNOWLEDGEMENTS ....................................................................................................2 PROGRAM ............................................................ ERROR! BOOKMARK NOT DEFINED. INTRODUCTION....................................................................................................................5 THE HUMAN SENSES IN SENSORY EVALUATION .....................................................7 THE SENSES - AN INTRODUCTION .................................................................................7 SENSE OF SIGHT- .................................................................................................................9 THE SENSE OF SMELL......................................................................................................13 THE SENSE OF TASTE.......................................................................................................15 THE SENSE OF HEARING.................................................................................................19 THE SENSE OF TOUCH .....................................................................................................20 SENSORY INTERACTION .................................................................................................21 OPERATIONAL PRINCIPLES OF SENSORY TESTING .............................................23 DESIGN OF A SENSORY TESTING AREA.....................................................................31 STATISTICAL PRINCIPLES .............................................................................................34 SENSORY EVALUATION METHODS .............................................................................38 AFFECTIVE TESTS .............................................................................................................38 SPECIFIC TEST METHODS ..............................................................................................39 PAIRED PREFERENCE TEST.......................................................................................39 RANKING FOR PREFERENCE.....................................................................................41 RATING FOR PREFERENCE ........................................................................................44 SENSORY EVALUATION IN CONSUMER TESTING ..................................................46 ANALYTICAL SENSORY TESTS: ....................................................................................53 DIFFERENCE TESTING.....................................................................................................53 SIMPLE DIFFERENCE TEST ............................................................................................53 TRIANGLE TEST .............................................................................................................53 DUO-TRIO TEST..............................................................................................................55 TWO-OUT-OF-FIVE TEST.............................................................................................59 COPYRIGHT R L Mason and S M Nottingham 3

Sensory Evaluation “A” – “NOT A” TEST.......................................................................................................59 DIFFERENCE-FROM-CONTROL TEST (DFC) .........................................................59 DIRECTIONAL DIFFERENCE TESTS ............................................................................65 PAIRED COMPARISON TEST ......................................................................................65 RANKING TEST ...............................................................................................................67 RATING TEST ..................................................................................................................69 STATISTICS FOR SENSORY: DIFFERENCE TESTING .............................................73 DESCRIPTIVE TESTING ...................................................................................................76 STATISTICS FOR SENSORY: DESCRIPTIVE TESTING ............................................81 SELECTION, TRAINING AND MOTIVATION OF A PANEL .....................................86 REPORTING .........................................................................................................................91 SELECTED BIBLIOGRAPHY............................................................................................92 JOURNALS ............................................................................................................................94 STATISTICAL TABLES......................................................................................................95

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Sensory Evaluation INTRODUCTION Sensory evaluation - A scientific discipline used to evoke, measure, analyse and interpret reactions to those characteristics of foods and materials as they are perceived by the senses of sight, smell, taste, touch and hearing. Sensory evaluation was one of the earliest methods of quality control and it is still widely used in industry. However, the level of application depends on the situation (e.g. beer and wine tasting to operators sampling of products from production line). Four variables affect sensory evaluation: • • • •

The Food The People The Testing Environment Methods

Sensory evaluation terminology • • • • • •

Sensory evaluation Sensory Analysis Organoleptic Analysis Taste Testing Psychophysics Subjective Evaluation

Advantages • • • • •

Gives real answer regarding consumer quality Relatively cheap process (depending on how it is done) Rapid Many applications Objective methods are more reliable, accurate and reproducible. However, they must be correlated to sensory evaluation to indicate a consumer response.

Disadvantages • • • • •

Time consuming Expensive to run Method selection Analysis Interpretation

Industry applications of sensory evaluation • • •

Product development Product matching Product improvement

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Sensory Evaluation • • • • • • • • • •

Process change Cost reduction New raw materials selection Quality control Storage stability Product grading / rating Consumer acceptance Consumer preference Panel selection / training Correlation subjective / objective

Sensory Standards Aus Standard

Year

Title

AS 2542.0

1995

Sensory analysis of foods - Introduction and list of methods

AS 2542.1.1

1984

Sensory analysis of foods - General guide to methodology General requirements

AS 2542.1.2

1984

Sensory analysis of foods - General guide to methodology Types and choice of test

AS 2542.1.3

1995

Sensory analysis of foods - General guide to methodology Selection of assessors

AS 2542.2.1

1982

Sensory analysis of foods - Specific methods - Paired comparison test

AS 2542.2.2

1983

Sensory analysis of foods - Specific methods - Triangle test

AS 2542.2.3

1988

Sensory analysis of foods - Specific methods - Rating

AS 2542.2.4

1988

Sensory analysis of foods - Specific methods - Duo-trio test

AS 2542.2.5

1991

Sensory analysis of foods - Specific methods - 'A not A' test

AS 2542.2.6

1995

Sensory analysis of foods - Specific methods - Ranking

AS 2542.3

1989

Sensory analysis of foods - Glossary of terms

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Sensory Evaluation THE HUMAN SENSES IN SENSORY EVALUATION THE SENSES - AN INTRODUCTION The sensory properties of foods are related to three major attributes: • • •

Appearance - colour, size, shape; Flavour - odour, taste; and Texture - mouth feel, viscosity and hearing.

These attributes are expressed as a continuum and not as finite properties. It is impossible to rate each one individually unless special precautions are taken, e.g. blindfolds, nose clips, coloured lights, purees.

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Sensory Evaluation Humans possess about 30 different senses. However, the sensory properties of foods are perceived through the senses of: • • • • •

Sight; Smell; Taste; Touch; and Hearing.

Stimuli A stimulus is any chemical or physical activator that causes a response in a receptor, e.g. eye is receptor for light, ear is receptor for sound. An effective stimulus produces a sensation, the dimensions of which are: • • • •

Intensity/strength; Extent/separation; Duration/retention; and Hedonics/like-dislike.

Receptors Receptors are the stimuli detecting cells of the sense organ, e.g. taste buds on tongue, light receptors in retina of eye. Perception Perception is the psychological interpretation of sensations determined by comparison with past experiences, e.g. the sour taste of lemons is the perception of the sensation received by the receptors (taste buds) from a chemical stimulus (citric acid).

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Sensory Evaluation SENSE OF SIGHTThe appearance of food Stimuli = visible light Receptor= retina of the eye Perception=sight, vision, appearance The appearance of foods is a major factor governing its acceptability and can be subdivided into three main categories: • Optical properties- colour, gloss and translucency • Physical form-shape and size • Mode of presentation-lighting packaging etc Optical properties Vision Vision is a complex phenomena consisting of several basic components. A stimulus, light, from an external source interacts with the object and is brought to focus on the retina of the eye. The retina is the receptor of vision and contains two types of cells. The rods are responsible for vision in dim light and the cones are responsible for colour vision. Light incident on these cells causes a photochemical reaction that generates an electrical impulse which is transmitted to the brain via the optic nerve. Colour blindness is caused by loss or lack of colour receptor cells in the cones. Approximately 8% of the population have some defect with relation to colour; mostly males.

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Sensory Evaluation Light Visible light is that part of the electromagnetic spectrum which radiates between wavelengths of 380 - 770 nm. Different wavelengths produce different colours 380 450 500 575 590

- 450 nm - 475 nm - 575 nm — 590 nm — 770 nm

=violet =blue =green =yellow = red

[NOTE: All electromagnetic radiations are physically the same. However, the optical system of the eye is such that only the visible range of wavelengths is absorbed by the lens.] Light sources Incandescent lights consist of a tungsten filament which is heated in an inert gas. The higher the temperature, the more light produced. Light from this source tends to be harsh and tends to highlight the red end of the spectrum. Fluorescent lights operate by electrical excitation of atoms that produces spectral lines at specific wavelengths which then impinge onto fluorescent materials which convert the incident light into light at a longer wavelength. Light produced is softer but can produce colour distortion at particular wavelengths. Natural light is too variable for use in evaluating appearance of foods. Light - Object interactions Light incident on an object may be: • • • •

Absorbed; Reflected; Transmitted; and Refracted.

The relationship between and within each of these components is responsible for the colour and gloss characteristics of the food. The main light/object interactions produced are: Lightness/value; Colour/hue; Chroma/purity; and Gloss. Physical form The second class of product appearance is physical form that can be subdivided into three parts: COPYRIGHT

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Sensory Evaluation • • •

Shape; Surface texture; and Visual consistency.

Shape and size are important from a food technologist's point of view because these can be altered during the manufacture of processed products. Some examples include: • • • •

Sliced, diced, pieces whole Length of frozen French fries Cut of beans Extrusions

Surface texture can indicate product texture. Some examples include: • • •

Open dry structure of meat Wrinkling of peas Wilting of lettuce

Visual consistency can indicate product viscosity as in: • • •

Setting of a jelly Syrups of different concentrations Pastes and purees

Mode of presentation This aspect should be considered from a marketing point of view and is important because it influences sales. Mode of presentation is applicable on the supermarket shelf (at retail level) and also in terms of presentation at the table (home and restaurant). Factors to be considered are: • • • •

Product description - name, price, ingredient, etc; Packaging - shape, design, colour; Contrast - phenomena of adjacent colours; and Illumination - affects apparent product colour.

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Sensory Evaluation Summary Appearance is an important aspect of food quality as it is the first subjective evaluation made of food quality. The product has to pass the visual assessment before the consumer can or will consider the other parameters such as taste and texture. Factors that should be considered in evaluating product appearance include: • • • • • • • •

use of standard conditions: light source (type, intensity, colour); background; and style of presentation (unless tested). selection of appearance attribute(s) for inclusion on scoresheet; using appearance to reduce tasting load; should be masked to eliminate unwanted interactions when assessing parameters involving other senses; and colour charts/standards help rating.

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Sensory Evaluation THE SENSE OF SMELL (Odour/olfaction) Stimuli = volatile chemicals Receptors= olfactory cells in the nose Perception=smell, odour, aroma, flavour Smell is one of our most primate senses. influenced by smell than other senses.

Supposedly prehistoric people were more

The human nose is capable of detecting thousands of different odour substances. However, our sensitivity is much less than other animals. (Animals use smell - food, mating, territory etc). Smell is detected both before and during eating. Smell is an important aspect of flavour. There are 20x106 olfactory receptors, but only about 1000 taste receptors. Odour description requires the development of an odour/flavour memory, e.g. fishy, flowery, woody. This is the basis of flavour/odour memory development by wine judges and milk/cheese graders. Individuals vary a great deal in their sensitivity to different odours/aromas. Anatomy of olfactory system

From the diagram it can be seen that most of air misses the olfactory area. Only 5-10% of inspired air passes over olfactory receptors. However, this amount can be increased by sniffing harder; obviously the more air which passes over the receptors the better the COPYRIGHT

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Sensory Evaluation response. The large number of olfactory receptors (20x106) enable detection of : • • •

More odours than tastes; A greater variety of odours; and Odours at much lower concentration (10 molecules/mL).

In order for odour to register: • • • •

Substance needs to be volatile enough to get into air in the sensory region. Substance needs to be partially soluble in mucus covering of receptors. Minimum number of odorous molecules need to be present. Need to be in contact with receptors for minimum time.

Olfactory intensity Human nose is about 10-100 times more sensitive to odours than any physico-chemical analysis (e.g. gas chromatography). It has been demonstrated that human nose is capable of detecting ethyl mercaptan at a concentration of 0.01 mg/230m3 of air, which is equivalent to about 8 molecules/receptor. Olfactory threshold Detection threshold is the concentration where smell is detected. Recognition threshold is the concentration where the smell is recognised. Olfactory interactions Nature of the response may change with concentration (e.g. perfumes at low concentration are pleasant but at strong concentration may be unpleasant). Interaction of odours: • Additive - increase intensity; • Suppressive - decrease intensity; and • Blending - when new odour unrelated to originals. Olfactory adaptation Initial sensation maybe strong - but weakens and makes identification difficult; this is due to adaptation of olfactory receptors. In testing we therefore need to allow for this by: • Taking first impression of odour and/or • Waiting between tests to allow receptors to recover.

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Sensory Evaluation Summary •

Smell is a major component of food flavour.

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Human nose is much more sensitive than analytical instruments.

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Foods contain numerous compounds of varying volatility that can make analytical interpretation difficult (e.g. strong peaks may produce weak odour whereas weak peaks may produce a strong odour).

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Smell measures perception of a mixture; analytical testing does not.

THE SENSE OF TASTE (Gustation) Stimuli = soluble chemicals or chemicals which are solublised during chewing Receptors= taste buds in mouth Perception=taste, flavour What is commonly referred to as taste/flavour is actually a combination of: • • • •

Taste; Smell; Touch; and Temperature.

Strictly speaking taste involves only those sensations mediated by the Gustatory Nerve Fibres and these sensations have five (5) basic qualities: • • • • •

Salt; Sweet; Sour; and Bitter. Umami

Taste stimuli Taste response requires an aqueous solution of the substance (stimulus) to contact the taste buds. Therefore, saliva secretions are important in terms of ensuring contact between the product and the taste buds. Saliva production is generally stimulated by chewing, as well as the appearance and odour of the food. The tongue is important as it brings the food into contact with the taste buds and also provides a mixing action which enables an even distribution of food about the taste buds as well as preventing the development of concentration gradients.

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Sensory Evaluation Taste receptors The receptors for taste are the taste buds and these are mounted on papillae (folds in the skin of the tongue). The area of greatest response is the top of the tongue. Other areas in the mouth and throat where taste buds are situated include: palate, pharynx, larynx, tonsils, epiglottis, lips, cheeks, underside of tongue and floor of mouth.

Taste buds are mainly located at the tip, sides and rear of tongue. There is very little response in the centre of the tongue. Different areas of the tongue are most responsive to different sensations. • • • •

Tip Sides Sides Rear -

sweet salty sour bitter

Taste cells constantly degenerate and regenerate. Their life cycle is 10 days and they are easily destroyed by heat. The tongue itself is important as it brings the food into contact with the taste buds and also provides a mixing action which enables an even distribution of food about the taste buds as well as preventing the development of concentration gradients.

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Sensory Evaluation The five basic tastes A basic taste is one for which specific taste buds have been identified as being physiologically responsible for the particular taste sensation. Sourness This is the simplest taste as only acids (H+) produce sourness and as the (H+) increases the sourness increases However there are some anomalies to this: • • • • • • •

organic acids are more acidic than expected. sourness of aliphatic organic acids relates to chain length. some amino acids are sweet (aspartane) picric acid is bitter sugar may enhance/depress sourness sourness is also affected by pH and acid presence of buffers affects sourness

Sweetness The common substances that produce the sweet taste are the sugars and other hydroxy compounds such as alcohols and glycols. Other substances such as lead salts, amino acids, proteins, non-nutritive sweeteners (cyclamates, saccharin and aspartame ) also taste sweet. Saltiness Many crystalline water-soluble salts yield a salty taste, but only sodium chloride gives a pure salty taste. Other substances taste salty but also bitter, alkaline, sweet and salt in various combinations. Bitterness Many chemically different compounds have a bitter taste. However, bitterness is mainly associated with alkaloids such as caffeine, quinine, strychnine and nicotine. Originally it was thought that bitterness was an indication of danger (poison). However, many alkaloids are used as drugs (e.g. codeine) and many other bitter substances are harmless (glycosides, esters and aldehydes and tannins in wines and tea). Bitterness is generally perceived at very low concentration and a relationship appears to exist between sweet and bitter as many sweet substances produce a bitter aftertaste (saccharin). Bitterness is the taste which most people have difficulty in detecting and response level varies greatly from individual to individual.

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Sensory Evaluation Umami Umami is the taste that has been shown to be associated with substances that contain glutamate. The most notable example is mono-sodium glutamate (MSG). MSG is well known as a flavour enhancer and can cause adverse reactions in some sensitive individuals. However, there are many other compounds which contain glutamate and which are capable of producing the savoury, spicy, brothy taste associated with MSG. Many foods contain naturally high levels of glutamate. Taste interactions Having described the 5 basic tastes it is obvious that foods are a very complex system which contain many different taste compounds and therefore many different tastes. The fact that there are only 5 basic tastes and yet we are able to detect hundreds of different taste sensations is due to a series of complex taste interactions that can range from simple 2 way interactions to complex 5 way interactions Interactions between the 4 basic tastes were previously described simplistically by the taste tetrahedron. Adaptation and fatigue During exposure to a stimulus, sensitivity decreases due to adaptation and fatigue. This loss in sensitivity varies considerably with the taste (sweet, sour, salty or bitter) and also with the compound. For example, tasting a series of acids causes the sensitivity to be reduced by the preceding acids. However, recovery is usually rapid because most common organic acids are very soluble. Taste thresholds and sensitivity There is great variability between individuals in their levels of sensitivity. Sensitivity is affected by: • Temperature; • Sleep; • Hunger; • Age; and • Sex. Absolute/Detection threshold - Concentration of stimulus at which a subject can detect a difference between two samples in a paired test. Recognition threshold - Concentration at which the specific taste can be identified. Recognition threshold is generally higher than detection threshold. Both absolute threshold and recognition threshold will vary between individuals. Most people can detect taste within 0.2 - 0.6 seconds and therefore if there is no response within this time the level is sub-threshold. However, recognition times vary between the basic tastes

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Sensory Evaluation • • • • • • •

Salt = 0.3s Sweet = 0.4s Sour = 0.5s Bitter = 1.0s Vision = 0.02s Hearing = 0.01s Touch = 0.005s

Reaction times also relate to retention times for example; bitterness has the longest reaction time (1.0s) and the sensation lingers considerably after tasting. Summary •

·Five types of taste receptors - salt, sweet, sour, bitter and umami.

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·Different areas of the tongue respond to different sensations.

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·Substances must be dissolved for taste buds to detect them.

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·Flavour of the food is a complex interaction of different tastes and odours.

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·Sensitivity to taste varies between individuals and is affected by their physiological state.

THE SENSE OF HEARING (Audition) Stimuli = physical movement of sound waves in a medium (air) Receptor= ear drum Perception=sound, hearing Hearing Sound is the perception by humans of vibrations in a physical medium (air). The sound of food when it is being eaten is an important aspect in determining quality. Positive aspects: • • • •

Snap, crackle and pop; Fizz of champagne or beer; Crispiness of lettuce or celery; and Tapping a melon for quality.

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Sensory Evaluation Negative aspects: noisy environment may distract tasters or mask product sounds. THE SENSE OF TOUCH (Texture, Kinesthetics) Stimuli = physical contact between the food and body tissue Receptors= muscles and nerves in mouth and fingers Perception=touch, feel, texture, viscosity Texture usually relates to solid food while viscosity relates to homogeneous liquid foods and consistency relates to non-homogeneous liquid foods. Instrumental methods only measure one aspect of "texture" and again cannot relate the complex interactions which produce the perception of food texture. Finger feel Firmness/Softness indicates the eating quality of some food products: • • • •

Ripeness level of fruit such as avocado and mango; Crumb texture of bread; Firmness of cheese; and Spreadability of butter or spread.

Juiciness can be used as a subjective quality index (eg the “thumbnail” test for corn). Mouth feel Liquids • •

Viscosity - thin to viscous, e.g. milk, cream. Consistency - thin to thick, e.g. fruit yoghurts.

Solids Classification of textural characteristics - assessed mainly by chewing. Textural Terminology

Mechanical Characteristics

Hardness

Soft, firm, hard, e.g. fruit ripeness, cheese maturity.

Brittleness

Crumbly, crunchy, brittle, e.g. muesli bars and biscuits

Chewiness

Tender, chewy, tough, e.g. meat.

Grittiness COPYRIGHT

Gritty, grainy, coarse, e.g. stone cells in fruit, "sand" in ice-cream. R L Mason and S M Nottingham 20

Sensory Evaluation Fibrousness

Fibrous, cellular, e.g. string/fibre in vegetables.

Moistness

Dry, moist, wet, e.g. cracker biscuit, cheeses, water melon.

Oiliness/Greasiness

Oily, greasy, fatty, e.g. french fries, chips.

SENSORY INTERACTION As has been indicated previously when eating or tasting food there is a continuous relationship between the senses and unless steps are taken to separate the individual senses or stimuli, interactions may occur. It is not known whether interactions occur at the receptor site or the brain. However, the second option would appear to be more likely. Interaction between senses This is the ability of a response from one modality to influence or affect the response from another. There are two aspects of this: Positive - interactions giving clues to possible identity, e.g. pink milkshake being strawberry flavoured. Negative - If clues are not correct this may lead to confusion and a wrong judgement, e.g. pink milkshake with pineapple flavour. Types of sensory interactions Taste - odour Receptors for these two senses are very close so that interactions between these senses are highly likely and these may be important in classifying a particular taste. Taste - tactile The taste threshold for sugar, salt, caffeine have all been shown to be lower in water than in tomato sauce. This may be due to the fact that in more viscous solutions the chemicals do not react with the receptors as easily as in pure solutions. Taste - sight This is a very important aspect because vision is the first sense affected and appearance of a product will have a major influence on absolute quality. Bright colours indicate strong flavours whereas dull colours indicate mild flavours. Other interactions include: • • •

Odour - Sight Odour - Tactile Taste – Hearing

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Sensory Evaluation •

Odour - Hearing

Multiple interactions Multiple interactions between more than two modalities are also possible. Example: Tasting food pureed, blindfolded and with nose clips gives a different response than when interactions are allowed. Interactions between stimuli These interactions are more difficult to define and measure but are just as important as interactions between the senses. Some examples include: •

suppression of one flavour by another, e.g. sweetness is suppressed by acidity. This is the basis of ensuring brix/acid ratio for fruit juices are constant;

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neutralisation of one flavour by another;

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blending to produce a totally different flavour, e.g. garlic flavoured cheeses;

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partial blending producing a new flavour and the original flavours;

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no effect; original flavours are distinct and separate, e.g. fruit in cheese;

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intensification resulting in enhancement of flavours, e.g. salt and MSG on food improves the natural flavours.

Similar situations may exist for all other stimuli. Summary Interaction must be considered when designing sensory panels. If only one sense or stimulus is to be evaluated then all others must be masked. However, if interactions are required then ensure this can be achieved by means of sample preparation.

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Sensory Evaluation OPERATIONAL PRINCIPLES OF SENSORY TESTING When evaluating properties of foods using people as measuring instruments it is important to control the methods and conditions of testing as rigidly as possibly. This helps to eliminate the numerous errors or biases that can be caused by psychological and physiological factors. The mental attitude and physical condition of a taster, and the atmosphere of the testing environment all influence their judgements. There are therefore a number of basic rules which should always be applied, as stringently as circumstances allow, when running taste panels. These relate to: • • • • •

Selection of panellists; Preparing the testing environment; Designing the experiment; Preparing samples; Serving samples.

General principles that should always be followed are: Never ask anyone to taste food they do not like; Make sure that the "correct" panellists are selected (see section on panel selection and training) and that they know in advance when they will be required. Keep a strict control over all variables except those being tested (e.g. sample size and temperature). Make sure the environment gives optimum opportunity for concentration. Tasting properly is a difficult job. Train panellists to be silent while tasting. This prevents panellists from influencing one another. Make tasting interesting and desirable. Use rewards to motivate taters, vary these and choose foods that contrast with those being tasted. Motivated tasters are more efficient. Give feedback on results whenever possible. Avoid giving any unnecessary information to panellists that may influence their scores. Tasters usually find what they expect to find; e.g. in a storage test they expect to find samples deteriorating. Plan your experiment in advance. Which will be the best test to use? Consider all aspects including how you will get the information required from your results (statistics). Run preliminary tests, i.e. practise and choose the best method for: Sample size - adequate but not excessive; Serving temperature - standardise for all samples. acceptable temperature for the food; Serving vessels; Eating utensils.

It must be maintainable, and be an

Sample preparation and serving COPYRIGHT

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Sensory Evaluation Serve tasters promptly and make sure they have everything they need. Run a taste panel as you would expect a good restaurant to be run, i.e. give courteous friendly service, be efficient, and serve good food. Keep accurate records of any cooking or preparation methods used. Record temperatures and size of samples served and any special conditions (e.g. coloured lighting). It is important that panellists do not see the samples being prepared as this may indicate quality difference. Sample preparation should be uniform: • • • •

Temperature Cooking Thawing Size and shape (provided this is not a variable)

Sample should be randomly allocated to: • •

Avoid bias Overcome any non—uniformity

Sample size should be adequate: • •

30g solids 30mL liquids

Samples should be served immediately after preparation to reduce: • • •

Flavour loss Discoloration Textural changes

Sufficient samples should be prepared to allow for seconds

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Sensory Evaluation Containers for presentation Containers for presentation and tasting should be: • • • • •

Clean Identical for all samples and sessions Disposable containers or re—usable Coloured to mask product appearance (if required) Relevant to product

Serving temperature • • • •

Serve at room temperature where possible Preference tests use normal temperature Difference tests may alter temperature to accentuate flavours/odours Do not overheat:

too hot to taste drying out off flavours browning

Dilutions and Carriers Most foods should be served in the way they are normally eaten. However, some products such as spices, chillies, alcohol, onions, etc. may require dilution before testing. If dilutions are used they must be uniform in terms of diluent and concentration. Carriers are substances that are added to assist tasting of certain products. Carriers are a problem because they can be: • • • •

Expensive Time consuming Variable quality Difficult to control product/carriers ratio uniformity.

For example: developing a cake icing individually may not allow for interaction with flavour or it may be incompatible with the cake (affects texture or falls off). Number of samples Samples / Sessions The number of samples presented at any testing session will depend on: • • • •

Type of product - strong flavour —> less samples Type of test Rating scale may require fewer samples Test dictates sample number eg: triangle test = 3 samples

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Sensory Evaluation • •

Type of panel — trained / experienced -> more Experimental design

As a general rule usually not more than 6 samples/sessions. Sessions / Trials Before starting your scheduled tasting sessions run two preliminary sessions. These will familiarise your panel with the scoresheet, the products to be tested and the procedures you wish them to follow. It also gives you practice at preparing and serving the quantity of samples needed, and a last chance to iron out any unforeseen problems. In calculating the number of sessions consider the following: • • • • •

Total number of samples for tasting Statistical design Taster fatigue Motivation Type of panel (trained/untrained)

Phsiological factors in taste testing Time of Tests • • • • •

Monday and Friday are recognised as being bad days for tasting Normally taste 1 hour before meals and 1 - 2 hours after Sometimes this becomes difficult in practice due to: Unavailability of tasters Number of sessions

Smoking / Taste Affecting Substances As indicated earlier, smoking affects sensitivity to flavours —therefore should either: • • •

Not use smokers Ensure they do not smoke for at least 1 - 2 hours before tasting Chewing gum, mints and spices etc may also influence taste

Illness Sensitivity of people suffering from illness is reduced -particularly those with colds or flu (physical and psychological) Likes / Dislikes In preference testing a series of treatments within a specific product type, it is legitimate to eliminate people who dislike the product (or those who are not discriminatory). Palate Clearing COPYRIGHT

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Sensory Evaluation It is a good idea to get panellists to cleanse their palate: • • •

Before tasting to remove any lingering tastes Between samples to reduce adaptation of taste buds. Warm water, biscuits, bread, apples may be used as a palate cleaning agent.

Palate clearing can be optional but whatever is done must be constant. The time between samples should also be kept constant if possible Perfumes / Spices Ask panellists to refrain from wearing strong perfumes or breathing spicy odours wherever possible. Psychological factors Because sensory evaluation is a subjective system, it is necessary to allow for any psychological factors that may influence results and possibly lead to errors. Motivation Good results can only be obtained from a co-operative, responsive panel. Tasting becomes a chore when there are large numbers of samples/sessions involved. Motivating panellists by can reduce this problem by: • • • • • • • • •

Stressing importance of work Stimulating company expansion Greater profits More pay Ensuring panellists know what is involved with the trial ie: sessions, products, when and where tasting will be conducted Having adequate facilities Using effective methods and designs Publicising results obtained from work Rewarding panellists

Sample Coding Remove possible bias or influence from samples codes. Do not use. • • •

Single digit numbers Consecutive letters Same codes at consecutive sessions

Randomly or statistically generated three digit number codes are best. Order of Presentation Always use either a random order of presentation or a statistically balanced design to avoid: COPYRIGHT

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Sensory Evaluation • • •

Donkey vote (first is best; last is worst) Position bias - in triangle tests middle one is different Contrast effect — good after bad appears better, or bad after good appears worse.

Devise your own system for remembering orders, e.g. 3 digit numbers - put in sequence of one of digits. Keep it a secret! Always work systematically in coding, labelling, setting up, e.g. as in reading a page (1) (2)

Left to Right Top to Bottom

This provides an automatic check if something goes wrong. Balance presentation of samples whenever possible. This avoids contrast effect. ie.

2 samples A, B.

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3 samples -

Half panel taste A first, other half taste B first. Half panel receive A on the left, other half receive B on the left. 6 different orders in which they are tasted. Use every order the same number of times. Number of tasters is a multiple of six. Position of samples on plate must also be balanced.

4 samples

24 different orders: use them all if possible (see table on next page).

4 samples

Generate random order. Write out set of cards and shuffle them.

When you cannot use balance to eliminate bias, use randomisation.

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Sensory Evaluation Four sample balanced orders 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

A A A A A A B B B B B B C C C C C C D D D D D D

B B C C D D A A C C D D A A B B D D A A B B C C

C D B D B C C D A D A C B D A D A B B C A C A B

D C D B C B D C D A C A D B D A B A C B C A B A

Expectation Error Any information a panellist receives before a test will influence the results. This is called expectation error. To overcome this: • • •

Do not give detailed information about treatments Do not use people on panel who know what the treatments are Sample coding and design can prevent expectation error

Logical / Stimulus Error Tasters look for clues to get the “right” answer eg: a difference in sweetness may be associated with sample differences such as size, shape and colour. This error can be overcome by ensuring sample preparation is uniform or use masking. Halo Effect When more than one factor in a sample is evaluated at one time the result obtained may be different than if factors evaluated separately. This can be overcome by tasting each aspect separately. However, this is time consuming and would only be done if extremely accurate results were required. Testing one aspect at a time in preference does not simulate the “real COPYRIGHT R L Mason and S M Nottingham 29

Sensory Evaluation situation” ie: consumers do not taste every aspect separately. Suggestion Influence of other panellist may bias or influence results. This can be prevented by: • • •

Using booths Not allowing talking in tasting area Reducing outside distractions

Questionnaire design Questionnaire design should be simple and easy to follow in terms of design and language and make sure tasters know how to use it. You may need to include some instructions on the scoresheet itself, but it is usually better to give instructions verbally to your panel first. The questionnaire should generally not be more than one page and include: • • • • • • •

Name Date Time Product Sample codes Instructions Comments section

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Sensory Evaluation DESIGN OF A SENSORY TESTING AREA The main considerations to keep in mind when preparing an area for sensory testing concern the requirements for an atmosphere conducive to concentration, where conditions can be controlled. Sensory panellists need somewhere comfortable and free from distractions if they are to be able to "tune in" to the sensations triggered by the stimuli in the food products they are tasting. Product characteristics can be markedly affected by temperature and humidity, and appearance is affected by lighting intensity. The conditions should be controlled in order to : • Reduce bias • Improve accuracy • Improve sensitivity • (compare to the conditions used in an analytical laboratory) International standard (ISO 8589-1988) The standard looks at the design of the testing area for both new and existing buildings. It also specifies which recommendations are considered essential and which are only desirable. Important points summarised from the standard are listed below. If designing an area that is to be dedicated solely to taste panel work, these should be seriously considered. Total area should include: • • • • • •

Testing area with individual booths and a group area; Preparation area/kitchen; Office; Cloakroom; Rest room; and Toilets.

General testing area •

Easily accessible but in quiet position.

•

Location - close proximity to preparation area, but separate entrance, and with complete "close-off" capability.

•

Temperature and relative humidity - constant, controllable, and comfortable.

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Noise - keep to a minimum, soundproof area as much as possible.

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Odours - keep area free from odours (air conditioner with carbon filters, slight positive pressure).

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Use odourless materials in construction and decoration.

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Use odourless cleaning agents.

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Sensory Evaluation •

Decoration - use neutral, light colours for walls and furniture (e.g. off-white, light grey).

•

Lighting - ambient lighting must be uniform, shadow-free and controllable. For consumer testing - as close to home conditions as possible.

Booths Number - minimum three, normally five to ten - six is a useful number since it fits in well with balanced ordering of 3 samples. Space - allow sufficient space for movement of tasters and for serving samples. Set-up - permanent booths recommended. Temporary acceptable. If adjacent to preparation area include openings in the wall to pass samples through. Size and style specified. Consider space for samples, utensils, spittoons, rinsing agents, scoresheets and pens, computerised equipment. Include comfortable seats. Lighting - uniform, shadow-free, controllable, adequate intensity for assessing appearance. Devices to mask appearance (e.g. dimmers, coloured lights or filters). Group work area General Necessary for discussion and training purposes. Include large table and several chairs. "Lazy Susan" useful. Include board for discussion notes, etc. Lighting

As for general area, with coloured lighting options like booths.

Preparation area General Located close to assessment areas but no access to tasters. Design for efficient work-flow. Well ventilated. Flexible services (i.e. plumbing, gas, electricity). Equipment Depending on testing required. Include working surfaces, sinks, cooking equipment, refrigerator, freezer, dishwasher, etc. Storage space for crockery etc. Crockery, glassware etc for serving samples. Office area General Separate but close to testing area, reasonable size, desk, filing cabinet, computer, bookcase. Photocopying service needed. Additional areas Useful to include rest room, cloak room and toilets. Practical alternatives The requirements specified in the International Standard (ISO 8589) will obviously provide a suitable area, but they are not always feasible, either from the point of view of financial COPYRIGHT

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Sensory Evaluation resources or physical space available. Very few industries are able to start from scratch, designing new premises solely dedicated to sensory analysis work. I therefore would like to abbreviate the list proposed in the standard to one which I consider includes the bare essentials. Minimum of 2 areas: Preparation area and office area. If possible position these at opposite ends of the room to avoid messy paperwork! Testing area with entrance separate from preparation area. Preparation area requires • • • • • • • •

Adequate storage for utensils and equipment; Adequate working surfaces to set out samples; Washing up facilities - minimum double sink with hot and cold running water; Refrigerator - minimum 2 door with separate freezer, preferably at least auto-defrost; Cooking equipment - depending on sample requirements; Rubbish bin - large with liner bags; Source of boiling water; Hand washing facilities.

Testing area requires • • • • • •

Comfortable chairs for panellists; Minimum space - 4 panellists; Table which can be easily divided into booths if required; All equipment likely to be needed while a panellist is tasting, e.g. pencils, spittoons, toothpicks, tissues/serviettes; Well placed, efficient lighting; Waiting are with noticeboard - for tasters to wait for booths to become free and to collect rewards after tasting.

A system using collapsible booths can work quite well if it is not possible to keep an area solely for sensory work. These may be made of painted wood, heavy duty cardboard, or "corflute". They can be made specifically to fit any available benches or tables and folded and stored when not in use. The type of facility will depend on: • • • •

Finance Available space Frequency of use Tests conducted

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Sensory Evaluation STATISTICAL PRINCIPLES This section looks at the role of statistics in sensory evaluation and introduces some terms and concepts required to correctly apply statistical methods in evaluating sensory type data. Why do we need statistics in sensory evaluation? When we measure something (eg salt level in cheese) we find there is variation in what we are measuring. This variation is called natural variation or experimental error and implies that there is some true measurement but because of our limitations we cannot reproduce the correct readings every time. This is a fact of life and we have limited control over this sort of error. Because of this variation there is some risk in making decisions about changing formulations or introducing new products onto the market. Using statistics we have rules to estimate and minimise the risk and enable us to extrapolate our results from an experiment to a more general situation. What is an experiment? It is any process that generates raw data. There are many sources of error in sensory data. Some of these include. • • • • •

differences between people, (likes and dislikes) differences within a person from time to time, eg adaptation differences among samples, differences in interpretations of scales and many more.

How can we describe our data? Lets say we have collected some data from an experiment and we have 20 scores of flavour acceptability in a mango sample rated on a 9 point hedonic scale. If we plot a bar graph (histogram) using the score along the horizontal axis and the count for a particular score on the vertical axis then we have a frequency distribution. An example is shown below.

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Sensory Evaluation 6

Frequency

5 4 3 2 1 0 3

4

5

6

7

8

9

Flavour Acceptability

Looking at the graph or distribution we ask what is the best single estimate of the panels score and what is a good measure of their variability? The best or most likely single estimates are called measures of central tendency. The three most commonly used are: mean - or average (sum of all data values divided by number of observations) median - 50th percentile or middle value mode - most frequent value, good for categorical data Measures of variability include the range, standard deviation and variance. The range is simply the difference between the smallest and the largest. The standard deviation is probably the most common and is calculated by using the formula below. s=

∑

( X − M )2 ( N − 1)

where M is the mean or average of X scores and N is the number of scores. This formula calculates the deviation of each score from the mean and squares it to take into account positive and negative values and the square root is then taken to bring it back to the original units. The variance is simply the square of the standard deviation and is used in a number of statistical formulas.

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Sensory Evaluation The normal distribution Many things we measure about a group of people will be normally distributed. This means they will form a bell shaped curve described by an equation usually attributed to Gauss. How does the standard deviation relate to the normal distribution? Standard deviations describe discrete percentages of observations at certain degrees of difference from the mean. So for a normal distribution about 66% of our data will be within one standard deviation of the mean and about 95% will be within two standard deviations. For our mango flavour data with a mean of 6.0 and standard deviation of 1.89 then 66% of our data lie between 4.11 and 7.89. If the standard deviation had been 1.00 then 66% of the values would be between 5.0 and 7.0, a smaller range indicating less variability. In addition any score, X can be described in terms of a z-value, which describes how far the score is from the mean in standard deviation units. Z = X-µ/σ Since z-scores are related to percentages under the normal curve they can predict how far a score is from the mean and how likely or unlikely it is. So the z-score can be converted to a probability value or p – value. This p - value is found from the area under the curve outside the z score and is the chance with which we would see a score of that size or greater. Tables are often used to convert z - scores to p – values. An important concept When we do an experiment we are using results from a sample taken from a larger population of possible results. Since we cannot take all possible results from the population we infer from our sample results what should happen in the rest of the population. By making this generalisation we often express our results in terms of probability or p- values. This is our safety margin or level of confidence about our result. It is often quoted like this the flavour score for naturally ripened mango was significantly higher (P 100 assessors use t test or CHI squared)

Disadvantages •

Only suitable for 2 products (note – multiple Comparisons can be used but other preferences tests are more commonly used. See ASTM manual on sensory testing method, STP 434; 1968)

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No magnitude of preference is given ie they both may be disliked but one can still be preferred.

Applications • • •

Product Development Product Matching Process Change

RANKING FOR PREFERENCE (Australian Standard 2542.2.6) Principle: Judges are asked to rank two or more samples in order or preference ie: most preferred sample is ranked first. Ranking is a forced choice procedure ie no ties are allowed. Specimen Answer form for ranking for preference. PRODUCT………………….DATE…………..TIME………ASSESSOR…… …………….. Please taste the samples in the order presented, moving from left to right and rank them in order of preference. You may retaste the samples to check the ranking. Give the sample that you most prefer the a rank of 1 and the sample you prefer next a rank of 2 etc. You must give each sample a different rank. Equal ranks are not allowed. Samples Rank

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Sensory Evaluation Statistical analysis Kramer’s tables, which have been used in the past to analyses differences between rank sums, should not be used due to questions of accuracy and statistical validity. When there is no expectation of a specific rank order being made (eg when ranking preference of new product prototypes) the Friedman Test should be used (see statistical method s section for details). Example Twelve households were presented with four samples of meat seasoning to be used in cooking. They were asked to use the samples as directed and to rank them in order of preference. The results are shown below:

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Sensory Evaluation Rankings for the preference of four meat seasonings HOUSHOLD 1 2 3 4 5 6 7 8 9 10 11 12 Rank sums

Seasoning A 1 2 1 1 2 3 3 3 1 1 1 1 20

B 3 1 4 4 3 4 4 4 2 2 2 3 36

C 2 3 2 2 1 2 2 1 3 3 3 2 26

D 4 4 3 3 4 1 1 2 4 4 4 4 38

The F value is calculated as follows: 12 (20 2 + 36 2 + 26 2 + 38 2 ) − 3 × 12(4 + 1) F= 12 × 4(4 + 1) =190.8-180 =10.8 the calculated value is compared to the critical f value in table 7 (7.81 for 3 df). since 10.8 is greater than 7.81, the experimenter can conclude that there is a significant (p