EVALUATION OF FLAVOURS IN DENTAL CREAMS 275 finding that concentration at which each taste is first detected. Thresholds vary considerably over the population and typical distributions found during the screening of candidates for a flavour profile panel are shown in Figs. 3, 4, 5 and 6. The distribution for bitterness is fairly flat and that for sweetness highly peaked. Adaptation and fatigue to flavours limit the number of and interval between tastings that any single panel member can be expected to carry out. Recovery from sour taste is usually very rapid because of the high solubility of hydrogen ion and the ease with which it is washed from the vicinity of the taste buds. Saltiness and sweetness present few problems as 12- I0- 8- 6- 4- 2- O- 0.04 0.09 0'18 0.:55 0.70 1.40 % citric ocid Figure 3. Sourness. 14- 12- I0- 8- 6- 4-- 2- O• I o,13 0,25 0.50 I.OO 2.00 4,00 % sodium chloride Figure 4. Saltiness.

276 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 0.1:5 0.25 0.50 1.00 2.00 •,'00 % sucrose Figure 5. Sweetness. 12- I0- 8- 6- 4 2 0 0.156 0.313 0'625 I.:50 :'500 5.000 % quinine sulphate (xlO -3} Figure 6. Bitterness. recovery from these sensations is also fairly quick. Bitterness can linger in the mouth for a minute or more, probably because bitter compounds tend also to be substantive to the skin and disappear more slowly from the site where they are tasted (6). The odour component of flavours presents the least problem from this point of view, recovery from odour sensation being quick. It has been reported that more than 70 odours can be evaluated in 1 h, provided that interest is maintained (7). Tactile and temperature, not to mention pain, stimuli present the greatest obstacle to carrying out many flavour evaluations in a short time. The cooling and tingling effects of menthol considerably slow the rates at which toothpastes can be tasted.