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5 - Laboratory methods for sensory analysis of food notes

5 - Laboratory methods for sensory analysis of food notes -...

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LABORATORY METHODS FOR SENSORY ANALYSIS OF FOOD ___________________________________________________________________ FACTORS INFLUENCING SENSORY MEASUREMENTS (pg 2) Standard procedures for planning and conducting sensory panels have been developed in an effort to minimize or control the effect that psychological errors and physical conditions can have on human judgement. The need for standardized procedures can perhaps be emphasized by describing some of the factors that affect human judgement and by outlining ways in which to minimize or eliminate them. Expectation error Any info that panellists receive about the test can influence the results. Panellists usually find what they expect to find. Therefore, give panellists only enough info for them to conduct the test. Do not include on the panel those persons who are directly involved with the experiment. Code the samples so that the panellists cannot ID them, as the code itself should introduce no bias. Because people generally associate “1” or “A” with “best”, we recommend the use of three-digit random numbers. Stimulus error In a desire to be right, the judgement of the panel members may be influenced by irrelevant characteristics of the samples. For example, when asked if there is a difference in the sweetness of two samples of peach halves, a panellist may look for help in every possible way such as the following: Are the pieces of uniform size? Is there a difference in colour? Is one firmer than the other? Because of this stimulus error, make all samples as uniform as possible. If unwanted differences occur between samples, mask them whenever possible. Logical error Closely associated with stimulus error is logical error, which can cause the panellist to assign ratings to particular characteristics b/c they appear to be logically associated with other characteristics. A slight yellow colour in dehydrated potatoes, for example, might indicate oxidation to the panellist who could logically find a different flavour in the sample. Control this error by keeping the samples uniform and masking differences. Leniency error This error occurs when panellists rate products based on their feelings about the researcher, in effect ignoring product differences. Therefore, conduct tests in a controlled, professional manner. Halo effect (pg 3) Evaluating more than one factor in a sample may produce a halo effect. The panellist often forms a general impression of a product and if asked to evaluate it for odour, texture, colour, and taste at the same time, the results may differ from those when each factor is rated individually. In effect, the rating of one factor influences the rating of another. For example, in meat evaluations, often panellists will rate a dry sample tougher than it would be if tenderness alone were being assessed. When resources allow, eliminate this effect by evaluating only one characteristic at a time.
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