FOODS 6.1 INTRODUCTION 6.2 WHAT IS SENSORY EVALUATION? Structure

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1 PRACTICAL 6 Structure SENSORY EVALUATION OF FOODS 6.1 Introduction 6.2 What is Sensory Evaluation? 6.3 Various Tests Involved in the 6.4 Techniques of Sensory Evaluation 6.5 Requirements for the Evaluation Process 6.6 Taste Sensitivity 6.7 Descriptive Analysis 6.8 Product Descriptors Activity 1: Determination of the Taste Threshold for the Different Sensations Sweet, Salty and Sour Activity 2: Conduct a Descriptive Analysis of the Given Sample of White Bread on the Basis of its Sensory Attributes. 6.1 INTRODUCTION In Unit 8, in the theory course (MFN-008), you may recall studying that when the quality of a food product is assessed by means of human sensory organs, the evaluation is said to be sensory or subjective or organoleptic. Sensory quality is a combination of different senses of perception coming into play in choosing and eating a food. This practical will focus on the sensory evaluation of foods. We will see how the individual threshold for different sensations varies from individual to individual. We suggest, before you start this practical, look up the quality attributes of foods as discussed in Unit 8 and also the description on sensory evaluation presented in Unit 14 in section 14.4 in the course MFN-008. Objectives After studying this practical and undertaking the activities included in this practical, you will be able to: perceive about the individual differences existing for taste stimulation, and recognize your own threshold and identification level for different taste stimulations. 6.2 WHAT IS SENSORY EVALUATION? have several characteristics that require evaluation by sensory methods. The various food attributes that are judged on the sensory scale are flavour, texture, aroma and appearance. Every time the food is eaten, the quality is evaluated or the judgment is made. The reaction of the consumer on the basis of the sensory perception serves as an endorsement or proof of the product acceptance. The sensory evaluation of food is carried out on a scientific basis to ascertain the product formulations or processing techniques that are anticipated to be successful in the market place. In the research and development process of a product, trained sensory panelists evaluate the samples and provide guidance in improvement of the product. This type of testing wherein the scores are determined by individual decisions based on the use of senses and do not rely on the mechanical devices, is known as sensory or subjective evaluation. Thus, sensory evaluation has been defined as a scientific method to evoke, measure, analyze and interpret those responses to products as perceived through the senses of sight, smell, touch, taste and hearing (Stone and Sidel, 1995). Sensory receptors such as olfactory receptors, taste receptors and visual receptors are used to study the following attributes of food: 1) Appearance 101

2 Principles of Food Science 2) Taste 3) Flavour 4) Texture 5) Consistency You may recall studying about these attributes in Unit 8 in the theory course. Here, let us briefly review these attributes. 1) Appearance The appearance of a food can be evaluated in terms of colour, surface characteristics such as smoothness of a surface, dry surface, glossy surface or the exterior appearance such as lump formation, thickness or thinness, layering etc. 2) Taste Individuals respond to a product on the basis of their sensory perception and judge the product quality differently. The auditory sense is the least used in appreciation of food quality, however, the senses for taste stimulation has a strong influence on the acceptability of food quality. Taste is sensed by taste buds, which you may already know by now, are located in the papillae on the tongue. Taste buds are located in the epithelium and on the parts of the tongue where the food contacts the most during chewing and swallowing. Taste sensations which the taste buds register are sweet, salt, sour and bitter. Taste buds near the tip of the tongue are more sensitive to sweet and salt, those on the sides to sour and those near the back to bitter, as illustrated in Figure ) Flavour Figure 6.1: Taste buds on tongue Flavour is composed of two subcategories, which are taste and odour. Flavour of a food is judged on the basis of the sensory message resulting from the combination of taste and aroma. The temperature at which the food is served may have a very important influence on the ability to detect taste and to evaluate flavour. The extremes, whether very hot or cold, limit the ability of people to judge food accurately. The best temperature range for flavour evaluation is C. However, some foods like ice creams should be evaluated at their serving temperature rather than at the temperature range ideal for detecting taste and odour. 4) Texture Texture indicates the characteristic of a food and would include descriptive parameters like graininess, softness, chewiness, brittleness etc. The textural qualities of a food have a relationship to the appearance of a product, as described previously and to its evaluation in the mouth as well. Mouthfeel would include the textural qualities of a food perceived in the mouth. 5) Consistency 102

3 Both texture and consistency characterize the mouthfeel of the product. As the term creamy indicates the consistency in an ice cream but is the textural attribute in the fudge. With a brief review on the different attributes of foods, we will move on to describe the various tests involved in sensory evaluation of food. 6.3 VARIOUS TESTS INVOLVED IN SENSORY EVALUATION OF FOODS Tests for sensory evaluation are of three types: Difference testing - This is the sensory testing designed to determine whether detectable differences exist between the products. Preference testing - It is the sensory testing to determine the acceptability or preference between products. Descriptive testing - It is the testing which provides information on selected characteristics of food samples. Look up Unit 14, sub-section in Course MFN-008 to get more details about these tests. We shall focus on techniques of sensory evaluation next. 6.4 TECHNIQUES OF SENSORY EVALUATION The various techniques used in the above mentioned tests for evaluation of food samples are given in Table 6.1. Table 6.1: Techniques of sensory evaluation Techniques Single sample Paired comparison Duo-trio test Triangle test Rank order Descriptive test Profiling Test characteristic This type of test is used to test acceptability and to aid in the decision on future development of the product. It is the difference test in which a specific characteristic is to be evaluated in two samples, and the sample with the greater level of that characteristic is to be identified. Difference test in which two samples are judged against a control to determine which of the two samples is different from the control. Difference test in which three samples (of which two are same), and the odd sample is to be identified. Preference or difference test in which all samples are ranked in order of intensity of a specific characteristic. Use of key or descriptive words in sensory evaluation to characterize food samples. It is a very detailed word description like texture profiling or flavour profiling or characteristics such as chewiness, adhesiveness, hardness. Descriptive scale It uses array of words describing a range of intensity of a single characteristic such as surface colour of a cake can be described as pale, slightly brown, pleasing golden brown, dark brown, burned etc. The scales can be designed with an odd number of points usually 5 or 9 point scales. The above example is that of a 5- point rating scale. Hedonic scale Hedonic rating range from unacceptable to very acceptable is relatively easy to construct and is effective when the desirable and undesirable characteristics of a few samples are taken into account. The 9 point 103

4 Principles of Food Science hedonic scale can be described as: 1= like extremely, 2= like very much, 3= like moderately, 4= like slightly, 5= neither like or dislike, 6= dislike slightly, 7= dislike moderately, 8= dislike very much, 9= dislike extremely Smiley scale This is a sequential series of very happy and continuing through to very unhappy faces used in evaluating food products when respondents are unable to use the language easily. The evaluation of food requires a careful analysis of the ways of assessing food, the properties of food, and the techniques for measuring these characteristics. Sensory evaluation gives guidelines for the preparation and serving of samples under controlled conditions so that the biasing factors are minimized. We will learn about the requirements for the evaluation process next. 6.5 REQUIREMENTS FOR THE EVALUATION PROCESS Some of the requirements to be kept in mind for the evaluation of the products are listed herewith: People in a sensory test are often placed in individual test booths so that the judgments they give are their own and do not reflect the opinions of those around them. Samples are labeled with random numbers so that the people they do not form judgments based on the labels but rather on their sensory experiences. Products may be given in different orders to each participant to help measure and counterbalance for the sequential effects of seeing one product after another. Standard procedures may be established for sample temperature, volume and spacing in time, as needed to control unwanted variation and improve test precision. Clear instructions should be provided to the panelists before the evaluation process as enumerated in Table 6.2. These instructions should be pretested by having someone unfamiliar with sensory testing. Instructions regarding the filling of the evaluation sheet should also be provided to the panelists. Table 6.2 : Instructions to the panelists S.No. Instructions 1. Please rinse your mouth with water before starting. 2. Different codes have been provided for sensory evaluation. 3. Taste each of the coded sample in the sequence presented. 4. Rinse your mouth with water and proceed to the next code. 5. You have to fill the evaluation performa code wise. In any evaluation process, the individual sensitivity to different taste sensations varies. Let us study more about this in our next section. 6.6 TASTE SENSITIVITY The concentration of a substance (in saliva) required to trigger the sensation of taste is much higher than the concentration of a substance (in air) required to provoke the sensation of odour. 104

5 The four primary tastes are not sensed equally. They are affected by time and concentration. For example, salt on the tongue is sensed in a fraction of a second, while bitter substance require a full second after it comes in contact with the tongue, however, these bitter sensations tend to linger for a longer duration than any other sensation. The concentration needed to bring about a sensation varies from one individual to another. The concentration required for identification is known as threshold. Individuals differ in their sensitivity to the four sensations, and the threshold for each of the four primary tastes is usually not at the same level in any of the individual. In the following activities we will see how the individual threshold for different sensations is varying. 6.7 DESCRIPTIVE ANALYSIS Sensory methods may be used to quantify the perceived intensities of the sensory attributes of a product. The quantification can be in terms of scaling of a product for different perceived sensations. This procedure of quantification is known as descriptive analysis. Descriptive analysis is generally used in situations where a detailed specification of the sensory attribute of a single product is required. These are frequently used in product development to measure how close a new variation is to the desired product. However, such testing requires trained panelist so that the results are consistent and reproducible. As descriptive analysis is very helpful in defining the quality attributes of a product and is required in the evaluation of variations during product development, thus, for your understanding we will conduct one activity to assess the sensory attribute of a product. Before we go into the details of product evaluation through descriptive analysis, we must be familiar with various descriptors or selecting terms used to describe the sensory attributes of the products. Let us get to know them. 6.8 PRODUCT DESCRIPTORS Descriptors are selected terms used to describe the sensory attributes of products and vary from one product to the other. The chosen descriptors should be non redundant with other terms and should have no overlap with other terms used. Descriptors should have certain desirable characteristics of being discriminating, representative of the product quality, precise and reliable, unambiguous and should easily relate to consumer acceptance or rejection. Descriptive analysis technique involves judging a product on the basis of its appearance, texture, taste, flavour and mouthfeel. It is a very helpful technique as the key words used are made to describe the product for a producible and consistent analysis. Although this technique involves both quantitative and qualitative analysis of food by using various methods as flavour profile technique/method, texture profile technique and so on. However, these type of descriptive analysis would require trained panelists for the purpose of evaluation. Thus, for our learning we would conduct a qualitative descriptive analysis of a product. For example, a slice of white bread in our activity 2 to understand the concept of food analysis. Before we start with the activity, let us list down various descriptors we would be using for a slice of white bread. 105

6 Principles of Food Science Example: A Slice of White Bread A slice of white bread should be evaluated on the basis of its appearance, taste, flavour, texture and mouthfeel. Let us take these attributes one by one to describe the product characteristics. Appearance As studied earlier in section 6.2 of this practical, the appearance of a product would involve colour (colour at the center and the colour of the crust), smoothness of the surface, and uniformity of pores, glossiness or shine. A slice of bread can be having white/creamy white colour at the center and the brown colour on the crust. The intensity of the colour can vary both in the center and the crust. A very light brown colour of the crust indicates inappropriate baking and a darker shade of brown will indicate over baking of the product. Smoothness/glossiness is the property of reflection of light from the surface and the scattering of light by the surface over different angles which indicates smoothness or roughness. Uniformity of pores indicate the moulding and fermentation of the bread dough. The smooth surface of the slice can also be related to uniformity of the surface. More the uniformity in the surface, more smooth it will appear and would reflect more light. The surface may seem quite shiny but would not have the mirrorlike reflection. Taste Senses for taste stimulation have a strong influence on the acceptability of food quality. The four primary tastes (sweet, salt, sour and bitter) are not sensed equally. They are affected by time and concentration. The concentration needed to bring about a sensation varies from one individual to another. Thus, the perception of each taste sensation varies from one individual to another. A product may be rated as sweet, less sweet, very sweet, depending on the individual s sensitivity to the sweet sensation. However, it is very important to characterize a product on the basis of the attributes it should have and then the product can be rated by various individuals. A slice of bread should be having a pleasant sweet taste. A sourish taste would indicate the over fermentation or spoilage of breads whereas, slightly bitter taste would indicate over baking of the product. Thus, the slice of bread can be evaluated in terms of intensity of sweetness, sourness and bitterness it is having. Texture Texture can be divided into oral texture which involves the mouthfeel characteristics, phase changes in the oral cavity and the tactile texture perceived when manipulating the object by hand. The overall texture of this slice of bread both by the sensation of eyes and taste can be included in the texture profile analysis. Before we go into the details of the texture profile, we must understand a few textural attributes and their definitions as indicated in the Table 6.3. Table 6.3 : Various texture attributes used in the process of evaluation S.No. Texture Attribute Definition 1. Adhesiveness Force required to separate individual pieces adhering to each other. 2. Wetness Amount of moisture perceived on the surface of the product, when in contact with the upper lip. 3. Roughness Degree of abrasiveness of the product s surface as perceived by the tongue. 4. Springiness Force with which sample returns to its original size and shape, after partial compression. 5. Cohesiveness Amount of deformation undergone by the material before rupture when biting completely through sample with molars. 6. Denseness Compactness of the cross section of the sample after biting completely through with molars. 7. Fracturability Force with which the sample ruptures when placed between 106

7 molars and bitten completely down at a fast rate. 8. Hardness Force required to bite completely through sample placed between molars. 9. Adhesiveness to teeth Amount of product adhering on/in the teeth after mastication of the product. Flavour Bread has its own characteristic baked flavour. This flavour diminishes with shelflife. A freshly baked bread would have intense baked flavour than the bread which is even one day old. With age, the flavour of bread changes from the baked flavour to sourish flavour, which is indicative of spoilage or ripening. Even a fresh slice of bread with over fermentation can have ripened flavour. Thus, the flavour can be assessed on the scale of pleasant baked aroma to sourish aroma. A key descriptor sheet is provided for your reference in the activity 2 wherein you would be conducting the sensory evaluation using this. Now, as you are familiar with the concept of sensory evaluation, let us get started with our first activity, which is determination of individual taste threshold. 107

8 Principles of Food Science ACTIVITY 1 Date:. DETERMINATION OF THE TASTE THRESHOLD FOR THE DIFFERENT SENSATIONS SWEET, SALTY, SOUR Aim: To determine the taste threshold for the three different sensations sweet, salty and sour. Objectives After conducting the activity included in this practical, you will be able to: perceive the individual differences existing for taste stimulation, and identify your own threshold and identification level for different taste stimulations. Principle Sensitivity threshold test: Sensitivity tests are used to assess the ability of an individual to detect the different tastes, odour and feel the presence of specific factors e.g. astringency tests are used to select and train panel members for evaluating the quality of products containing spices, salt, acid and sugar. For this purpose, threshold tests for the recognition of basic tastes or odours are employed for selecting the panel members. The threshold value is expressed numerically as: Intensity score key 0 Name or taste of pure water 1 Different from material but quality not identifiable 2 Threshold very weak (taste identification) 3 Weak taste 4 Medium 5 Strong 6 Very strong 7 Extremely strong These are two different taste thresholds. These include: 1) Stimulation threshold: In this state, the panel member recognizes the taste to be different from pure water but is unable to identify the taste due to dilution. 2) Identifiable threshold: Here the panel member is able to identify the taste quality as the taste is pronounced. The panel members are supplied with a series of beakers containing the increasing concentration of substances with 1 of 4 primary tastes. The member will start with beaker no. 1 and continue to taste the solution in other beakers in the increasing numerical order. Materials Required Salt solution (%) -0.5, 0.8, 1.0, 1.2, 1.5 Sugar solution (%) , 0.5, 0.7, 1.0, 1.2. Citric acid (%) , 0.04, 0.1, 0.5, 1.0 Spoons Bowls Beakers Plain distilled water Take a group of at least 10 subjects to carry out the process of sensory evaluation. 108

9 Procedure Now carry out the activity step-by-step as enumerated herewith: 1) Prepare different concentration of sugar (sweet), salt (salty) and citric acid (sour) as mentioned in the materials required. 2) The beakers should be placed in the increasing order of concentration. 3) The individual members tasting different concentrations should be having plain distilled water after each tasting. 4) The individual should mark their stimulation threshold and identifiable threshold in the observation table. Results and Observations Now note down your readings in the format given herewith. Under stimulation and identifiable threshold column in the heading, indicate the total subject participating in the exercise. Under different concertrations of stimulants, indicate the number of subjects (out of the total) able to recognize each of the solution concentration: S. No. Concentration (%) Stimulation threshold (by number of subjects) 1. Salt 0.5 Identifiable threshold (by number of subjects) Your Intensity score* Sugar Citric acid * Intensity score should be based on the 7-point scale given above under the principle. Inference 109

10 Principles of Food Science.. number of people were able to recognize the sweet taste at % sugar solution. number of people were able to recognize the salty taste at % salt solution. number of people were able to recognize the sour taste at % citric acid solution. Conclusion (Comment regarding your threshold and identification level) Submit the activity for evaluation. Counsellor Signature 110 ACTIV 2

11 CONDUCT A DESCRIPTIVE ANALYSIS OF A GIVEN SAMPLE OF WHITE BREAD ON THE BASIS OF ITS SENSORY ATTRIBUTES Aim: To sensory evaluate the slice of white bread on the basis of appearance, taste, texture and flavour. Objectives After conducting this activity, you will be able to: judge the product quality through sensory evaluation, and get familiarized with the use of various descriptors used in the evaluation process. Principle Refer section 6.7 and explain what do you understand by descriptive analysis in the space provided herewith. Date:. Refer to section 6.8 and describe what are descriptors in the space provided herewith: Materials Two different samples of white bread slices coded 001 and 002 Sheet for analysis Any instructions Glass of water Napkins Sample disposal arrangements Procedure Carry out the activity according to the steps enumerated herewith: 1) Read out the instructions carefully (provided in Table 6.2 given earlier in section 6.5). 2) Write the name and code of the sample provided at the top. 3) Fill in the descriptive evaluation proforma for each code separately. 4) Carry out your own individual sensory analysis for the given sample. 5) Take precautions while filling in the proforma for unbiased results. 6) Analyze the data for the product characteristics and report. 111

12 Principles of Food Science Observation Descriptive evaluation Proforma Sample identified as :.. Code of the sample provided :.. Sample size :.. Serving temperature :.. Tick mark the most closely describing anchor word for the listed attributes of the given sample: Evaluation criteria Attributes Anchor words Appearance Colour of the center of the slice white- creamy white Colour of the crust light brown-golden browndark brown Uniformity of pores uniform- non uniform Surface area smooth-rough Glossiness shiny-dull Feel hard-soft-sticky Taste Taste during chewing sweet-bland-sour After taste sour-bitter-sweet-none Texture Tissue adhesiveness sticky-tacky-gooey Brittleness crumbly- crunchy- brittle Chewiness tender- chewy- tough Elasticity/springiness spongy- elastic Hardness soft- firm- hard (dry) Flavour Flavour before and after biting pleasant baked flavour-sour -ripened flavour As you have conducted descriptive evaluation of code 001, next carry out the descriptive analysis for the code 002. Sample identified as :.. Code of the sample provided :.. Sample size :.. Serving temperature :.. Tick mark the most closely describing anchor word for the listed attributes of the given sample: Evaluation criteria Attributes Anchor words Appearance Colour of the center of the slice white- creamy white Colour of the crust light brown-golden browndark brown Uniformity of pores uniform- non uniform Surface area smooth-rough Glossiness shiny-dull Feel hard-soft-sticky Taste Taste during chewing sweet-bland-sour After taste sour-bitter-sweet-none Texture Tissue adhesiveness sticky-tacky-gooey Brittleness crumbly- crunchy- brittle Chewiness tender- chewy- tough Elasticity/springiness spongy- elastic Hardness soft- firm- hard (dry) Flavour Flavour before and after biting pleasant baked flavour-sour -ripened flavour 112

13 Now, when you have carried out the descriptive analysis for both the samples, study their product characteristics in detail. Report your findings in the table given below. S.No. Evaluation criteria Attributes Code 001 Code Appearance Colour of the center of the slice Colour of the crust Uniformity of pores Surface area Glossiness Feel 2. Taste Taste during chewing After taste 3. Texture Tissue adhesiveness Brittleness Chewiness Elasticity/springiness Hardness 4. Flavour Flavour before and after biting Interpretation: Code 001 Code 002 Conclusion Submit the activity for evaluation... Counsellor Signature 113