Nutrition & Food Science

Nutrition & Food Science Understanding consumer requirements for fruit and vegetable texture David KilcastLaurence Fillion

Article information: To cite this document: David KilcastLaurence Fillion, (2001),"Understanding consumer requirements for fruit and vegetable texture", Nutrition & Food Science, Vol. 31 Iss 5 pp. 221 - 225 Permanent link to this document: http://dx.doi.org/10.1108/00346650110396574 Downloaded on: 30 January 2016, At: 17:07 (PT) References: this document contains references to 17 other documents. To copy this document: [email protected] The fulltext of this document has been downloaded 914 times since 2006*

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Understanding consumer requirements for fruit and vegetable texture David Kilcast and Laurence Fillion


The authors David Kilcast is Head of Sensory and Consumer Science and Laurence Fillion is Senior Consumer Scientist, both in the Sensory and Consumer Science Group at the Leatherhead Food Research Association, Leatherhead, Surrey, UK. Keywords Consumer attitudes, Taste, Fruit, Vegetables Abstract Fruit and vegetables are important components of a healthy diet, and their textural characteristics are important in determining consumer choice. The food industry needs reliable instrumental methods to measure the textural quality of fresh produce, but also needs to ensure that the instruments measure characteristics important to consumers. A study was carried out to probe consumer understanding of textural characteristics, and to relate their perceptions to sensory profiles developed by trained panels. The results were correlated with instrumental texture measurements, and included sound emitted during fracture. Consumers had a clearer understanding of the nature of crunchiness, in contrast with crispness, and good correlations were found with the instrumental parameter, fracture toughness. Electronic access The current issue and full text archive of this journal is available at http://www.emerald-library.com/ft

Nutrition & Food Science Volume 31 . Number 5 . 2001 . pp. 221±225 # MCB University Press . ISSN 0034-6659

Background Several reports have highlighted the need for dietary change as a means of improving health in the UK (Department of Health, 1992; Scottish Office Home and Health Department, 1993). Increased consumption of fruit and vegetables is central to improving the UK diet, but consumption is not increasing as hoped. A research project carried out by the Leatherhead Food RA to investigate ways to increase consumption (MAFF Project A163; see Kilcast et al., 1996) identified sensory characteristics as an important limiting factor.

Sensory needs Most studies that have investigated the importance of different sensory modalities on consumer acceptability conclude that flavour is the most important modality, followed by texture and then appearance (e.g. Moskowitz and Krieger, 1995). Such conclusions do not reflect the enormous efforts that the food industry devotes to ensuring appealing textural characteristics, and to maintaining those characteristics in long-term supply and production. Research with consumers in the USA carried out by Szczesniak and Kahn (1971) showed that awareness of texture lies at a subconscious level, and that textural properties are taken for granted. If the expectations of texture are violated, however, awareness of textural defects are accentuated, and texture becomes a focal point for criticism and rejection of the food. Expectations are being increasingly recognised as an important factor in food choice by consumers (e.g. Vickers, 1991; Cardello, 1994). Textural characteristics are of great importance in the enjoyment of fruit and vegetables, and even minor deviations from the expected textural characteristics can result in the consumer rejecting the food. Characteristics such as crispness and crunchiness are regarded as key components of desirable texture for many fruits and vegetables, but unjustified assumptions are often made when identifying the key sensory The authors would like to thank the Ministry of Agriculture, Fisheries and Food for funding this project under contract number CSA 3958.

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Understanding consumer requirements for fruit and vegetable texture

Nutrition & Food Science Volume 31 . Number 5 . 2001 . 221±225

David Kilcast and Laurence Fillion

attributes that are important to consumers. These often do not take into account the difficulties in ensuring that vocabularies used by consumers and within industry have a strong correspondence. Words to describe textural attributes cause particular difficulties, and in solid foods there are known problems in the use of words such as crispy, crunchy and hard, and the relationships between these attributes are poorly understood.


Industrial needs for texture measurement Many sensory techniques are available for defining and measuring textural characteristics. The most commonly used require a trained panel to agree on the key texture attributes and their definitions, and to quantify their intensities. However, considerable difficulties are commonly encountered in securing agreement on texture attributes, resulting in lengthy and expensive panel training. Techniques such as free choice profiling have been developed to allow panellists to generate individual vocabularies, and sophisticated statistical analysis methods have been developed to assist interpretation. It is therefore unsurprising that the food industry has expended considerable efforts in developing instrumental texture measurement methods to minimise these problems of subjectivity. Early empirical methods of texture measurement did not correlate well with consumer perception of texture, and this situation persists despite the introduction of versatile instrumental measurement systems coupled with sophisticated computer software. One potential reason for this is the limited understanding of how the behaviour of the food under instrumental test relates to the behaviour during mastication. It has increasingly been thought that poor correlations between instrumental and sensory measurements could be a result of choice of instrumental tests that are inappropriate in simulating the oral chewing processes that characterise different foods. An additional complicating issue is that trained panels used to characterise perceived textures as a necessary step in validating instrumental measurements may not necessarily use the same vocabularies to describe individual textural attributes as consumers. The distance between the ideal overlap between consumer

perception, sensory assessment and instrumental measurement and the current reality is shown schematically in Figure 1. An additional consideration in understanding the consumer perception of fruit and vegetable texture is the potential importance of the sounds emitted when fresh produce is eaten (Figure 2). It is known that both the way in which the produce behaves and fractures when it is being eaten (Vincent, 1991) and the sound emitted during eating (Szczesniak, 1988) are important in influencing consumer acceptance, but this aspect has received little attention in improving texture measurement methods.

Project objectives The purpose of this MAFF-funded project was to use input from the field of materials science to understand more fully the mechanical components of texture, and to combine this with a better understanding of the consumer's perception of texture to design instrumental tests that would be more valid and reliable measures of this perception. The project involved a collaboration of scientists from the Leatherhead Food Research Association and the University of Reading Centre for Biomimetics, together with in-kind assistance from Stable Micro Systems Limited. A unique combination of skills and techniques in consumer science, sensory analysis and materials science was used throughout the project. Aspects investigated were: consumer perception and sensory characterisation of fruit and vegetable texture; importance of sound emission in Figure 1 The relationship between consumer, sensory and instrumental measurement

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Figure 2 Map of consumer perception of fruit and vegetable textures

texture perception and measurement; and the use of the underlying principles of fracture mechanics to design improved instrumental test methods.

Probing consumer understanding of texture Six products were selected for these experiments: carrot, celery, cucumber, green pepper, Granny Smith apple, and Golden Delicious apple, all freshly purchased from a local supermarket. Preparation included peeling (except for green pepper) and cutting into 1cm slices (carrot, cucumber and celery) or segments (apples and green pepper). Following a pilot study, ten consumers were recruited to give a wide range of ages and social classes. One-to-one interviews were performed using a simplified Repertory Grid Method as an interviewing technique. Pairs of different fruits and vegetables were presented to the respondents, so that all products were seen twice in different combinations, and respondents were asked to describe similarities and differences in texture. Respondents were not restricted in the manner in which they could bite into the product. A personal vocabulary, which was specific to each respondent, was then developed and definitions were agreed. This step was followed by a scoring session, where respondents were asked to rate each product on an intensity line scale for every attribute of their own glossary. For comparison purposes, the experiments were repeated using 11 trained panellists. Generalised Procrustes analysis (GPA) is a statistical method that allows meaningful

comparisons of individual vocabularies, by calibrating assessors in terms of scale use and rotating sample spaces for comparing different uses of terms. Results from interviews were analysed using GPA, and product and attribute maps were generated. Products that were close together on the map were interpreted as being perceived as similar in terms of texture. In the same way, attributes lying close to one another on the plot were used with a similar meaning by consumers. Both consumers and panellists found it very difficult to define crispy and crunchy terms and needed constant probing. However, all insisted that they could perceive a difference between the two, but then struggled to describe this difference, which indicated that it was only slight. Common aspects included a certain resistance to the teeth when biting or chewing, the emission of a sound and finally brittleness. In brief, crispy and crunchy are used to describe products that break rather than deform, and the way they fracture under the application of a force. In the case of fruits and vegetables, ``crunchy'' seems to be more universally used than ``crispy''. Some subjects associated crispy textures only with dry foods such as crisps and wafers, as opposed to wet foods. Both sensory and consumer data showed that there was poor agreement on the understanding and the use of crispy terms, while crunchy terms were used with a more similar meaning. Definitions used are summarised in Table I. Sound attributes were present in most definitions of both crispy and crunchy textures. However, the two attributes differed from each other by the type of sound involved, namely a low-pitch sound for crunchiness, and a high-pitch sound for crispness. This was not surprising, as Vickers (1984; 1985) described a similar difference. Loudness, on the other hand, did not seem to be taken into account when deciding whether a product was crunchy or crispy. Loudness was used rather to assess the intensity of crunchiness or crispness, as indicated by Drake (1963) and Vickers and Bourne (1976). It is well-known that the soft tissues of the mouth tend to dampen sounds by absorbing high frequencies (Vickers, 1984; Lee et al., 1988). The pitch of the sound emitted when biting into a product hence depends on the

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Table I Definitions of crispy and crunchy attributes from consumer and panellist interviews


Consumers (n = 10) Crunchy Crispy Number of subjects mentioning the attribute Assessment on front teeth only Assessment on back teeth only Number of times a descriptor was given Hard, dense Sound Loud Low pitch High pitch Repetition of sound Brittle Snap, clean break Light Fresh Moist

9

5 1

1 8 8 2

Panellists (n = 11) Crunchy Crispy 11 6

3

8 10 4 8

10 6 2

9 4 8

1 3 2 3 1

mouth's configuration, and whether the mouth is closed or open. If crispness is characterised by higher-pitched sounds, it can be expected to be more intense on first bite with the mouth open than when chewing on molars with the mouth closed, and the contrary can be expected to be true for crunchiness. Some subjects specified that crunchiness was mostly assessed when chewing on the back teeth, while crispness was rather perceived when first biting into the product with the front teeth. After sound, hardness was the second most important descriptor associated with crunchiness. On the other hand, a certain number of subjects related crispness to a lighter texture. One panellist contrasted the two attributes in these terms, describing crunchy as being ``thick and heavy'', while crispy was ``light and thin''. However, most subjects also insisted that crispy products were not soft, and that some resistance to the teeth was required, but not too much. Some people even mentioned that a very hard texture could not be perceived as crispy but would rather be described as crunchy. This was the case with the carrot data sets: when hardness was very high, there was a lack of correlation between hardness and crispness (see also Mohamed et al., 1982). This seems to be in agreement with a theory stating that crispy and crunchy textures are on the same continuum of hardness, with crispy products being intermediate and crunchy ones having a more pronounced hardness, with some possible overlapping of the two (Vincent, 1998).

5 3 8 6 1

Application to improved instrumental measurement Correlation studies were carried out to investigate the relationship between sensory texture attributes measured by the trained panel using sensory profiling and instrumental measures of texture. Three types of instrumental measures were investigated: force-deformation measurements using a Stable Micro Systems TA-HD2 Texture Analyser with an incisor probe; sound intensity measurement carried out during the force-deformation measurements; and measurement of fracture toughness and fracture energy using a single-notch bend test. Different fracture patterns associated with carrot, celery, cucumber and Granny Smith apple could be accounted for on the basis of microstructure features; the smaller the flaw or defect in the product, the higher the fracture stress. Confocal microscopy images of carrot showed that it has a smaller cellular structure than celery, cucumber or Granny Smith. In addition, because the cells are in intimate contact with neighbouring cells, the degree of adhesion is probably higher, resulting in fewer flaws or inhomogeneities. These flaws can act as stress concentrations and promote premature failure. This is reflected in the higher fracture parameter values for carrot, and the presence of a small number of large breaks and sound events. For cucumber, Granny Smith and, to a lesser extent, celery, the cellular structure shows that the cells are not in intimate contact and there are many

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larger sites where the shape of the cells prevents adjacent cell walls from touching. This gives rise to lower fracture stress and, in turn, relatively lower fracture parameter values for these products. In the case of celery, and Granny Smith to a lesser extent, the presence of fibres or air pockets, which act as a stopper to crack propagation, explains the large number of small breaks observed. Sound level and fracture toughness were found to be good predictors of sensory texture overall. However, the best predictor varied depending on the sensory attribute and the produce considered. Fracture toughness was a good predictor of crispy, crunchy and hard textures for apples and celery, but predicted only hardness of carrots and not their crispness and crunchiness. On the other hand, a reverse pattern was observed with sound level, where prediction was good for apples and carrots, except for hardness of carrots. However, in terms of quality, hardness of carrots is a more relevant texture attribute than crispness or crunchiness. Measurement of fracture toughness alone would therefore be suitable to assess the quality of all produce tested.

Implications for healthy eating Improved texture measurements that are strongly related to eating quality will help growers, manufacturers and retailers to supply more consistent products with a high level of acceptability, and will help to address increasingly important issues associated with the changing population demographics in Europe. It has been estimated that, within the next 25 years, the percentage of the population over the age of 60 will be higher than 25 per cent in Europe (Dichter, 1992). For the food industry, the ability to maintain market share in this segment will depend critically on meeting the needs of ageing consumers. The EUfunded HealthSense project was launched to investigate how age-related sensory loss affects people's choice of food, and how to tailor the flavour and texture of foods to people with decreased sensitivity. The role of Leatherhead Food RA focuses on problems associated with the texture of food and eating difficulties, and how to measure people's chewing capabilities. Combining an understanding of how people perceive the texture of food with an understanding of the difficulties that are

encountered in eating foods of nutritional importance will give the food industry increased opportunities to provide food of optimum eating quality and nutritionists a wider choice of dietary components.

References Cardello, A.V. (1994), ``Consumer expectations and their role in food acceptance'', in MacFie, H.J.H and Thomson, D.M.H. (Eds), Measurement of Food Preferences, Blackie Academic and Professional, London. Department of Health (1992), The Health of the Nation. A Strategy for Health in England, HMSO, London. Dichter, C.R. (1992), ``Designing foods for the elderly: an American view'', Nutrition Reviews, Vol. 50, pp. 480-83. Drake, B. (1963), ``Food crushing sounds. An introductory study'', Journal of Food Science, Vol. 28, pp. 233-41. Kilcast, D., Cathro, J. and Morris, L. (1996), ``Practical approaches to increasing vegetable consumption'', Nutrition & Food Science, Vol. 5, pp. 48-51. Lee, W.E. III, Deibel, A.E., Gemblin, C.T. and Munday, E.G. (1988), `Ànalysis of food crushing sounds during mastication: frequency-time studies'' Journal of Texture Studies, Vol. 19, pp. 27-38. Mohamed, A.A.A., Jowitt, R. and Brennan, J.G. (1982), `Ìnstrumental and sensory evaluation of crispness. II: In high moisture foods''. Journal of Food Engineering, Vol. 1, pp. 123-47. Moskowitz, H.R. and Krieger, B. (1995), ``The contributions of sensory liking to overall liking: an analysis of six food categories'', Food Quality and Preference, Vol. 6, pp. 83-90. Scottish Office Home and Health Department (1993), The Scottish Diet, HMSO, London. Szczesniak, A.S. (1988), ``The meaning of textural characteristics ± crispness'', Journal of Texture Studies, Vol. 19, pp. 51-9. Szczesniak A.S. and Kahn E.L. (1971), ``Consumer attitudes to and awareness of food texture 1: Adults'', Journal of Texture Studies, Vol. 2, pp. 280-95. Vickers, Z.M. (1984), ``Crispness and crunchiness: a difference in pitch?'', Journal of Texture Studies, Vol. 15, pp. 157-63. Vickers, Z.M. (1985), ``The relationship of pitch, loudness and eating technique to the judgement of the crispness and crunchiness of food sounds'', Journal of Texture Studies, Vol. 16, pp. 85-95. Vickers Z.M. (1991), ``Sound perceptions and food quality'', Journal of Food Quality, Vol. 14 No. 1, pp. 87-96. Vickers, Z.M. and Bourne, M.C. (1976), `À psychoacoustical theory of crispness'', Journal of Food Science, Vol. 41 No. 5, pp. 1158-64. Vincent, J.F.V. (1991), ``Texture of plants and fruits'', in Vincent, J.F.V. and Lillford, P.J. (Eds), Feeding and the Texture of Food, Cambridge University Press, Cambridge. Vincent, J.F.V. (1998), ``The quantification of crispness'', Journal of the Sciences of Food and Agriculture, Vol. 78, pp. 162-8.

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