SENSORY EVALUATION
variables, and succeeds in discarding laboratory trials which have evident defaults and reduces the number of variables on which the following tests must focus.
The consumer’s evaluation This testing instrument is generally very reliable, provided that questions are posed in the right way, but its limits are also very clear. First is the cost, as a minimum of 150 people are required for significant results. The second is the simplicity of the answers, as the type of questions that can be posed to standard consumers cannot be very complicated. For instance, we cannot ask: “How emollient is this cream?”, as the concept of emolliency is variable for each consumer. The same applies to: “How moisturising is this cream?”, as the consumer will perceive softness and smoothness of his skin, but not moisturisation.
These tests are very useful for testing concepts, packaging colours and shapes, and for getting general information regarding a product’s acceptance (hedonistic/liking variables).
Internal panels
Usually this is made up by a group of workers in the factory. They detect acceptability and application performances quite well, but here again their reference products are variable. They certainly know the products well and use them, but have a poor knowledge of the market. This is because people involved in the testing probably belong to a homogeneous social class, and are therefore unable to represent the consumers’ requirements in their entirety. The internal panels are used to avoid costly consumer tests but their reliability, even when a fairly high number of people are involved, is very poor and the judgment could be misleading. The lack of normalisation of responses leads to poor statistical significance.
Objective sensorial techniques From what has been described, the sensorial evaluation of the performances of cosmetics requires more sophisticated instruments. One instrument is a trained sensorial panel. It is composed by a group of people, specifically trained for a long period (6 months to one year) to detect, qualify and quantify perceptions developed during standard conditions of use of specific cosmetic products.
Selection and training of panellists is expensive and time consuming, but their reliability, reproducibility and precision of the evaluation almost always gives satisfactory answers to all aspects of perception. The lack of ability of the
108 PERSONAL CARE April 2012
Discriminative sensory techniques
These are very simple forms of sensorial tests, also used during the training phase of the panel. Panellists are requested to select from three products, one of which is used as reference, the sample which exactly matches the reference (duo-trio test).
sensorial trained panel to foresee the market acceptance of a product is the only limit, which should be well known when employing such an instrument. The selection of panellists must be carried out from a large pool of candidates, on the basis of their sensitivity to sensorial stimuli, their familiarity with the product category to be analysed, and on their ability to express concepts verbally. Panellists are also trained to detect the intensive variety of the stimuli, and to translate this intensity into marks over a linear scale. Following this, the group coordinator will transform these marks into numbers. Training requires continuous exercise, using the so-called reference products. During this period all the panel participants are trained to position on a scale, for a specific attribute, the reference samples, to repeat several times the right positioning, and introduce new references in the scales.
The panel is considered ready when repeated tests give the same results, with no statistical difference among the panellists. As reference products, common objects or food ingredients may be used (e.g. glass, paper, rubber, olive oil, flour, etc.).
During this phase the panellists develop also the so-called ‘common language’. They analyse all the sensorial variables related to the normal use of a finished product, they express them verbally and find a general agreement on the verbal terms which define independent variables. Avoiding overlapping of terms or misleading expressions is the task of the panel coordinator. He acts as ‘friendly controller’ leading the group without overbearing it, checking its results, deciding if and when further training is required, solving competition problems. When the panel is ready, it is possible to begin the analysis work.
The test becomes slightly more complex if the three samples are given without identifying the reference product (triangle test). Another is the Paired Comparison Test, in which each subject is given a product pair combination randomly. He or she is required to indicate the product in which an established sensorial feature shows the greater intensity. This can be repeated for many product pairs, so providing a ‘ranking test’. These tests are very useful:
For determining the panellists’ (or your marketing boss’) sensorial skill.
For controlling the storage stability of sensorial attributes (colour, spreadability) of a new product.
For controlling the perception of different percentages of perfume.
For detecting differences between industrial and laboratory batch.
For controlling if changes of some raw materials can perceivably affect the product feel.
For comparing qualitatively products having unknown differences in sensorial features.
These groups of tests are very interesting but, in some cases, incomplete. The typical answer given is that the products are different in some attributes (when they are so perceived) but the reason for such differences is not analysed in depth and the amount of the difference is also not known. For investigating these details more in depth, we need a more advanced instrument: the Quantitative Descriptive Analysis (QDA).
The QDA With this methodology, the sensory analysis enables, like any analytical science, to investigate in a quantitative, precise way the sensorial response to a specific stimulus. It is therefore possible to carry out a full analysis of all the sensorial attributes of a product.
Descriptive tests enable the evaluation of the sensorial features of a given sample, both from a qualitative (identification of the attributes) and quantitative point of view (intensity evaluation). They are quite complex tests, involving a group of panellists specifically trained to quantify and describe the sensorial perceptions induced by the product during an accurate
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