Sensory analysis of dairy foods.

Is sensory analysis a valuable tool to the dairy product manufacturer? M.A. Drake was invited by the American Dairy Science Association to review the work done on sensory appraisal. The title of his Review which was published in the Journal of Dairy Science, Volume 90 of 2007, page 4925 to 4937, was appropriately: Sensory Analysis of Dairy Foods.

Sensory perception in terms of at least texture, aroma, flavour and taste is an integral part of the success of dairy products in the market and therefore the use of just the best ingredients in this context is emphasized by the manufacturer. To that effect sensory measurement or appraisal is often the final step in evaluation, whether during the experimental phase of development or the final product that leaves the premises. It is, however, of concern that some manufacturers in modern times are still sceptical about the value of sensory analysis, and rather stick to their out-dated and poor discriminating (tasting) tests of a perceived experienced individual(s) or grader on the floor. It may also be a case of ignorance of what is available. Thus, it is probably of value to review the different sensory analysis techniques.

Dr Drake distinguishes between three basic categories or groups of tests. The first group includes traditional tools using grading and scorecard judging developed in the early 1900s. A product with the aid of these tools is assigned an overall quality score or grade based on a designated list of defects. Clearly, this is extremely qualitative but valuable in trouble shooting because it can be done quickly. The second group of tests are analytical sensory tests, consisting of the difference or discrimination test, the threshold test and the so-called descriptive analysis. In the difference test the sole objective is to determine if there is a difference between two or more products. Here a panel of 25 to 50 individuals is used, depending on the number of products to be tested. It is important to realize that this test is used when the nature of the difference is known (e.g. chocolate milks in which the sweetener concentration is the only difference). This test therefore cannot be used to determine consumer preference; for that purpose more sophisticated tests are required. The function of the threshold test is clear from the definition of threshold: it is the lowest concentration at which a sensory response is detectable. Threshold tests are most often applied to undesirable (e.g. off-flavour) or desirable components in foods. A typical example of undesirable is: at what concentration is dimethyl trisulfide an off-flavour in whey protein isolate? In general, threshold tests are a powerful tool to relate sensory perception to chemical analysis of volatile and non-volatile compounds. In descriptive analysis a group of 6 to 12 individuals are trained to identify and quantify specific sensory attributes or all sensory attributes of a food. The panellists are trained to operate in unison, with each panellist serving a function analogous to an individual sensor on an instrument to ensure that the results are as precise and reproducible as possible. A question that a descriptive panel for example can address is: should cheese firmness be measured by compression with fingers, bite force with incisors, bite force with molars, or compression between the tongue and the hard palate?

The third group of sensory tests is affective or consumer tests, in which a large array of specific and sensitive tools fit in. The uninformed would perceive this as simply measuring preference and liking, but the tests are actually far more expansive, diverse and complex. As implied, consumers are used and not trained panellists and their function is to convey to the manufacturer what consumers like or dislike. Obviously the number of consumers that are required to do the testing must be fairly large (50 plus) to be representative of the target consumer. To choose them is a science on its own because factors such as age, gender, product usage rate, income, ethnicity and product perceptions/attitudes need to be taken into account. Preference and acceptance tests are the most widely known group of quantitative consumer tests, In preference testing, consumers are presented with two or more samples and asked to indicate which sample they prefer. If more than two samples are presented, they can be requested to rank their preference. This is effective, but the test cannot distinguish the degree of liking. For that purpose acceptance testing is required, where consumers are asked to indicate their degree of liking on a scale, usually a 9-point hedonic scale. There are also other scales depending on the complexity of the question. Another group of quantitative consumer tests are conjoint analysis, the difference with preference and acceptance tests being that actual products are not required. Conjoint or trade-off analysis takes into account that consumers make choices or trade-offs between independent (yet conjoint) attributes in a product when making a purchase decision. The goal is to determine which product attributes are most important to the consumer, without having to manufacture prototypes. The final group of consumer research tools is qualitative tests. This is done with focus groups and interviews and the goal is to get insights into consumer perceptions, needs and desires which are important for product development.

Bottom line: The review showed that appropriate sensory techniques can be used to enhance product understanding, establish relationships between sensory and chemical measurements and enhance understanding of the consumer. The tests available are much more accurate and comprehensive than what can be identified by industry graders.