Sensory Measurements of Texture

1. Sensory Measurements of Texture

2. “Texture is the sensory and functional manifestation of the structural and mechanical properties of foods, detected through the senses of vision, hearing, touch, and kinesthetics.” Alina Surmacka Szczesniak (1963) “Texture is a sensory property. It is not the force needed to push a needle-like probe a certain distance into an apple, or the work necessary to disintegrate a handful of peas in a shear cell. Texture makes sense only when viewed as a sensory property or ‘how a food feels in the mouth’” Alina Surmacka Szczesniak (1998)

3. “Sensory methods are the ultimate method of calibrating instrumental methods of texture measurement . . . Sensory evaluation offers the opportunity to obtain a complete analysis of the textural properties of a food as perceived by the human senses. A number of processes occur while food is being masticated, including deformation, flow, comminution, mixing and hydration with saliva, and sometimes changes in temperature, size, shape, and surface roughness of the food particles. All of these are recorded with great sensitivity by the human senses, but many of them are difficult to measure by objective methods.” Malcom Bourne (1982) “Man is nothing but a bundle of sensations.” Protagoras (450 B. C.)

4. Importance of Sensory Measurements • Properties perceived by consumers of most importance to food quality • Objective measurements calibrated against human standards • Instruments not measure acceptability, likability, etc. • Processes in the mouth may change nature of the food (saliva, temperature, enzymes) • Mechanical actions of mouth difficult to duplicate

5. Disadvantages of Sensory Testing • Humans vary widely in sensitivity, likes and dislikes • Variables may be difficult to isolate (influence of color, taste, smell) • May be expensive, time consuming • Standards are not absolute

6. Types of Sensory Tests • Overall difference tests • Attribute difference tests • Qualitative affective tests • Quantitative affective tests • Acceptance tests

7. Sensory evaluation: using people as measuring tools • sensory evaluation panels • identify criteria; detect changes in product • consumer panels • assess product acceptability/desirability • consumer feedback • how does product match consumer demands

8. Sensory evaluation panels • highly trained • judge quality of product using internal or industry standards • untrained panels • evaluate new products for acceptability • evaluate effects of process or formula change (Are their differences?)

9. OVERALL DIFFERENCE TESTS • Designed to detect whether subjects can detect any difference amongst samples • Ex 1: Manufacturer substitutes carageenan for xanthan in yogurt. Can difference in texture be detected • Ex 2: Juice producer testing non-thermal pasteurization. Perceived differences in texture?

10. Triangle Test • Determine if overall differences between 2 products • Easy to do and analyze • 20 - 40 panelists typical; 8-12 for large differences • Similarity tests: 50 - 100 panelists

11. 3 Samples are presented, two are the same, one is different. • Random combinations of ABB, BAA, AAB, BBA, ABA, BAB are presented. • Panelists are asked to identify the odd sample. Subjects must guess if they cannot detect a difference. • The number of correct responses are tabulated and checked for significance. A B A

12. A A B B A Two Out of Five Test • Also for overall differences • Similar to triangle but more statistically efficient (smaller chance of guessing) • Can use smaller number of panelists • 5 coded samples; must select two samples that are different

13. Duo-Trio Tests • Simple, easy test, but less statitically efficient than triangle test • May need > 30 panelists • Reference sample presented, followed by two coded samples • Which sample matches reference?

14. Reference sample A B

15. Simple Difference Test • Effective when only two samples can be presented • Two samples presented • Panelists indicate whether samples are the same or not • Analysis: compare the number of “different” responses for matched pairs with the number of “different” responses for different pairs • Use 2 for analysis

16. Difference From Control Test • Determine difference between samples and a control • Good when size of difference is important • Panelists rate the size of the difference between each sample and the control

17. Control sample

18. ATTRIBUTE DIFFERENCE TESTS • Designed to detect whether a single attribute differes between, or amongst, samples • Hardness, viscosity, crispness, etc

19. Paired Comparison Test • Designed to determine in what way an attribute differs between samples (harder, less viscous, etc) • Simple, useful for screening • Often large number of panelists needed • 2 coded samples presented: which sample is harder, crisper, more cohesive, etc

20. A A A B B B D D D C C C Pairwise Ranking Test • Used to compare several samples for a single attribute (3-6 samples by inexperienced panelists) • Samples randomly presented, and in pairs Which sample is crispier? A___ B___

21. For a given pair, panelists asked which sample is more __________? • Freidman ranked sum analysis used • Results shown on a rank sum scale D C A B Not Crisp Very Crisp 40 50 60 70 80

22. D C B A Simple Ranking Tests • Several samples compared at once for a single attribute • Ranking data is ordinal • Samples presented in random order

23. Panelists rank the sample according to the attribute Rank sums are calculated and evaluated by Friedman’s test Rank the samples in order from least to most chewy. 1st__________ 2nd_________ 3rd__________ 4th__________

24. C B A Rating/ANOVA Approach • Panelists decide in what way an attribute varies over all the samples • Rate attribut on a numerical scale • Multiple samples presented in random order

25. 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 Panelists rate attribute on a cardinal scale Mark a line on the sliding scale for each sample to indicate how hard they are. B C A

26. BIB Ranking Test • Panelists determine in what way an attribute varies over all the samples • Useful when many samples exist • Samples presented in smaller groups according to a Cochran and Cox incomplete block design • Samples ranked according to attribute

27. AFFECTIVE TESTS • Used to determine consumer’s personal response to a product • Preference: does consumer like one product better than others • Acceptance: is the product one that a consumer finds acceptable, would buy, or would use • Consumers may find 2 products acceptable, but not prefer one over another. Also, panelists might prefer one product over others, yet none of them may be acceptable.

28. Some uses . . . • Product Maintenance: Does ingredient, process, or packaging changes affect the characteristics and acceptability of existing product? • Product Improvement: Are attempts to improve a product through formulation or process effective? • New Product Development: Are new products being developed acceptable to consumers? • Category Review: How does an existing product stack up against competiotive brands?

29. Conducted on group of subjects representative of larger target population • Factors • User group (e.g. sports drinks, baby foods) • Age • Gender • Household income • Geographic location • Ethnicity, education, employment

30. Qualitative Affective Tests • Measure subjective responses • Assess consumer’s initial response • Learn consumer terminology to describe products in their own words • Learn how consumers use a product

31. Focus Groups • Focus group consists of 10-12 consumers selected based on specific criteria • Subjects meet with moderator 1-2 hrs • Presents product and facilitates discussions • Responses summarized in written form • Often videotaped

32. Focus Panels • Focus group in which the panel discusses the product, is sent home to use it, then returns for further discussion

33. One-On-One Interviews • Consumers interviewed individually about their response to a product • Similar format, set of questions, etc used for each interviewee

34. QUANTITATIVE AFFECTIVE TESTS • Used to determine overall prefernce or liking for a product • Often used to determine preference or liking for broad aspects of a product, but may be used to measure particular sensory attributes • May be choice (preference) or rating (acceptance)

35. Preference Tests • Useful when one product is pitted against another • “Improved” product versus control • Do not indicate degree of liking

36. NUMBER OF TEST SAMPLES ACTION Paired Preference 2 Choose one sample over Another (A/B) Rank Preference 3 or more Rank in order of preference (B-A-C-D) Multiple Paired 3 or more Series of paired samples. One Preference sample chosen over the other for each pairing. Multiple Paired 3 or more As above, but series of samples Preference paired with selected samples.

37. Acceptance Tests • Determine how well a product is liked by consumers • Often similar to the attribute difference tests discussed previously, but the attribute is acceptance or liking • May be appropriate to infer prefence based on relative acceptance scores