Department of Surgery, Yale University School of Medicine, P.O. Box 208041, 333 Cedar Street, New Haven, Connecticut 06520-8041, USA
Taste blindness to phenylthiocarbamide (PTC) and its chemical
relative 6-
n-propylthiouracil (PROP) was discovered in the 1930s.
Family studies showed that those who could not taste PTC/PROP
(nontasters) carried two recessive alleles. In recent years,
we have classified tasters into two groups: medium (PROP is
moderately bitter) and supertasters (PROP is intensely bitter).
With our classification,
25% of Americans are nontasters, 50%,
medium tasters, and 25%, supertasters. Studies showed that supertasters
form a cohesive group. Anatomical studies showed that supertasters
have the most fungiform papillae. Psychophysical studies showed
that supertasters perceive the most intense bitterness and sweetness
from a variety of compounds, the most intense burn from oral
irritants, and the most intense tactile sensations from viscous
solutions. Oral burn and touch are presumably perceived to be
the most intense to supertasters because taste buds in fungiform
papillae are innervated by the trigeminal nerve (pain, touch)
as well as the chorda tympani nerve (taste).
The psychophysical scaling method used was magnitude matching with NaCl as the control modality. With this method, subjects rated the intensities of a series of NaCl and PROP solutions. The assumption that the taste of NaCl did not vary with PROP status allowed comparisons of the bitterness of PROP across subjects. Early magnitude matching studies, using sound as the control, had suggested that this assumption was reasonable. However, recent studies challenged that conclusion. Larger samples with more diverse populations, using sound as the control, showed that the taste of NaCl varied with PROP bitterness; supertasters perceived the strongest taste and nontasters, the weakest. Thus our earlier conclusions were conservative because differences between nontasters, medium tasters, and supertasters were concealed by using NaCl as a standard. Using magnitude matching with sound as the standard, or using the Green scale, which employs intensity labels, we found that the differences between PROP groups are larger. Note that the association between PROP status and salt taste is interesting in itself, since variability in salt taste may have important nutritional consequences.
