EVALUATION OF FLAVOURS IN DENTAL CREAMS 279 Thresholds for the four basic tastes are quite independent. Sensitivity to one particular taste does not necessarily imply sensitivity for any other taste. This effect is well known (10). As the four tastes are perceived by four totally separate systems of taste buds this is only to be expected. Tests designed to show whether phenylthiourea was perceived as bitter or tasteless and whether sodium benzoate was tasted as sour, sweet, salty or bitter gave the results shown in Fig. 7. These are what would be expected of an average population and the responses to the two compounds are again completely independent. Perception of phenylthiourea as bitter did not mean that sodium benzoate would also taste bitter to the same person. Sodium benzoate Sweet Sour Salt Bitter Total Phenylthiourea Bitter 9 2 3 14 28 Tasteless 4 2 1 4 11 Total 13 4 4 18 39 Figure 7 Having chosen the panel it is then necessary to train it. Training takes the form of running practice sessions on specially prepared toothpastes consisting of unflavoured bases of various types to which flavour com- ponents are added singly and in increasingly complicated combinations. In this way the panel builds up a vocabulary of flavour notes and gains practice in describing events in the mouth in terms of these notes. Sessions are best held in the hour before lunch and panel members should refrain from drinking, eating or smoking for at least 30 min before a tasting session. Hands should be washed before a session using water only and no soap. The session itself is composed of two parts. Aroma is evaluated first and flavour second. In both parts the odours, flavours and other sensations are identified and described as accurately as possible. An intensity rating from the scale 0 1 2 3 4 Not present Just noticeable Slight Moderate Strong is then awarded to each sensation. The order in which the sensations occurred is recorded and finally, aftertaste and after effects are noted. In the first session with any flavour a considerable amount of time will be spent on discussion within the panel to settle on an agreed nomenclature

280 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS for the observed sensations. At this point an independent supervisor for the panel is essential since forceful personalities on a panel can influence this stage considerably. With a trained panel, however, this problem can be avoided by using a version of the Delphi technique developed by the Rand Corporation (11). Each panel member carries out his evaluation in private, noting down sensations, time order and intensities on a blank form. After the first tasting the forms are collected and a questionnaire for the second tasting compiled which shows the order of sensations with their mean intensities as scored on the previous session and the ranges within which the panel rated the intensities. The panel member carries out his second tasting with all this information in front of him and modifies his evaluation in the light of this. Questionnaires for the third tasting are based on the results of the second in a similar fashion and the process repeated until the panel reaches a reasonable consensus. Three or four repetitions are usually enough to produce a satisfactorily tight range of evaluations from the panel. Peppermint Figure 8. Odour profile. Presentation of the results of flavour profile analysis traditionally made graphically in the form of profiles are shown in Figs. 8 and 9. The sensations are arranged from left to right around the circumference of a semicircle in the order in which they were recorded. Intensity is indicated by the length of sensation segment above the semicircle. An alternative form of presentation is merely to plot intensity against time and add descriptions of the sensations at appropriate points as shown in Fig. 10. Results can be depicted equally effectively as histograms.