Sensory Methods

Generally following sensory tests are adopted under different conditions.

•  Difference or discriminative tests
•  Scoring
•  Ranking
•  Hedonic scale
•  Descriptive analysis
•  Acceptance and preference test

 i. Difference or Discriminative Testing

Difference test is one of the most useful sensory tests. It is generally used for selection and training of sensory panelists. Difference test is designed to discriminate difference between two or more samples. Within this general class are a variety of specific methods, viz., paired comparison, duo-trio, triangle and multiple sample tests. The main features of these difference tests are discussed here.

a) Paired Comparison Test: It is a two products (e.g. A & B) test, and the panelist’s job is to compare these and identify whether the samples are similar of different. If different, which attribute, such as sweetness, acidity, hardness, colour etc. is responsible for this difference. This part of the test is called as directional difference test. The test can be further extended and the preference component of the panelist can be included. The paired comparison test is relatively easy to organize and implement. The two coded samples in order of AA, BB, AB, BA (4 pairs) are served simultaneously, and panelist has to decide if there is any difference or not. Paired comparison is typically used in comparing new and old processing techniques, change of ingredients in a product, preference testing at the consumer level, etc.

b) Duo-trio Test: This test is a modified paired comparison test. One sample identified as the reference (R) is first given to the panelists for evaluation.

Subsequently two coded samples, one of which is identical to reference, are presented. The panelist is asked to indicate, which of the two samples is the same as ‘R’. The test is suitable for products that have relatively intense odour, taste and/or kinesthetic effects such that sensitivity of evaluator is significantly reduced. It is used for quality control and for selection of panelists.

c) Triangle Test: Triangle test is most well known and more frequently used out of the three difference tests. As its name implies, it is a three product test in which all the samples are coded and the panelist’s task is to determine which two are most similar or which one is most different from the other two.Triangle test is more difficult test because the panelist must recall the sensory characteristics of two products before evaluating the third and then make a decision. It should, therefore, preferably be used by trained panel for quality control work, and also for further training of panelists.

d) Multiple Sample Test: Test involving more than 3 stimuli are classified as multiple sample tests. They may have equal (symmetrical) or unequal (asymmetrical) numbers of each stimulus. When they are applied as true difference tests, the judge is required to separate the sample into two groups of like samples. When they are applied as directional tests, the judge is asked to identify the groups of higher or lower intensity of a given criterion. Difference test designs involving more than three stimuli have only limited use. The limitation is due to the increase in psychological complexity and physiological fatigue, which accompanies an increase in number of stimuli. In addition, large quantities of samples are required and more time is needed. Multiple sample test is more applicable to visual differentiation and also to odour evaluation.

ii. Scoring

Certain weightage or score is given to each sensory attribute arranged in logical order on a score sheet in this method. The weightage is given on the basis of importance of the attribute. For example, flavour is considered to be most important and highest score is allotted to this attribute. The scoring method is most extensively used by the dairy industry (score cards of many dairy products will be given in Unit 3). Score cards wherein 10 to 100 total points have been allotted to different quality attributes are in use for dairy and food products. Scoring method is most frequently used amongst all sensory methods because of its diversity, simplicity and ease of statistical analysis. The most attractive feature of this method is that rigorous training is not required for panelists as information on defects and scoring guide is also provided on the scorecard.

iii. Ranking

In ranking method two or more samples are provided to the panelists who are asked to arrange them in an ascending or descending order of intensity of a specific attribute, e.g. sweetness. Ranking is often used for screening inferior from superior samples in product development. This method is also suited for comparison of market samples of different brands and ranking them first, second and so on. Samples may be ranked in order of degree of acceptability or in order of general quality or by a specific attribute. Example of ranking 5 samples of spongy Rasogolla is given below.

Sample codes, 237, 255, 287, 291 and 296

So, using ranking test, Rasogolla with desired (optimum) sponginess can be selected.The ranking test is most effective if only one or two attributes are compared and the difference between samples is too large.

iv. Hedonic Rating

Hedonic relates to the psychology of pleasurable and non pleasant states of consciousness. In hedonic method, psychological states of like and dislike are measured on a rating scale. Normally rating scale has been categorized into five forms, viz. numerical, graphic, standard, cumulated points and forced choice forms. The Nine points numerical scale as given below has been most extensively used for new product development and consumer studies.

Like extremely                      9

Like very much                     8

Like moderately                    7

Like slightly                           6

Neither like nor dislike           5

Dislike slightly                        4

Dislike moderately                 3

Dislike very much                  2

Dislike extremely                    1

The above scale can be modified by assigning a numerical value of 0 to the indifferent category, with positive integers above and negative integers below this point. The use of positive and negative type of scoring can be effectively used by only trained panel. The hedonic scale provides following advantages:

• evaluators can respond to the queries without previous experience 
• data can be handled statistically, and 
• indicates general level of preference or liking for the samples

 The only requirement for use of hedonic method is that large number of evaluators are needed to provide reliable responses or results.

v. Descriptive Analysis

Descriptive method of sensory evaluation provides quantitative descriptions of a product based on the perception of a group of qualified judges. It is a total sensory description of a product taking into account all sensation that are perceived: visual, auditory, olfactory, gustatory, kinesthetic and so on. A descriptive method enables us to relate specific process variables to specific changes in some of the sensory attributes of a product, for example, the flavour changes in milk at high temperature processing. From the view point of product development, a descriptive information is essential in finding out those product variables that are different and from which one can establish the cause and effect relationships.

A descriptive test involves relatively few judges, who have been screened, selected and trained for the particular product category. Training of this group is primarily focused on development of descriptive language, which is used as a basis for scoring a new product, developing a definition of each attribute and familiarizing the judges with scoring procedures. There are numerous applications for descriptive analysis including monitoring competitions, storage stability/shelf life, product development, quality control, establishing physical/chemical and sensory correlation.Some of the popularly used descriptive method are Flavour profile, Texture profile, Quantitative descriptive analysis, etc.

vi. Acceptance/Preference Testing

Affective or acceptance testing is a valuable sensory technique, usually performed at consumer’s levels. It refers to measuring liking or preference for a product. Preference can be measured directly by comparison of two or more products with each other. Indirect measurement of preference is achieved by determining which product has scored significantly higher rating than another product in a multi product test. The two methods most frequently used to directly measure preference and acceptance are the paired comparison test and a 9-points hedonic scale.Both these methods have been discussed earlier.