The genetically inherited trait defines the ability to taste the bitter compounds: 6-n-propylthiouracil (PROP) and phenylthiocarbamide (PTC)8
. PROP is a compound containing the N-C=S group7
. It is odorless and less poisonous than PTC. Due to those characteristics of PROP, it has been substituted for the use of PTC based on the suggestion of R. Fisher in 19632
. The structure of PROP is shown in Figure 1.
Figure 1. Chemical structure of PROP7
Genetic variation in PROP sensitivity can be assessed by the taste of bitterness of PROP and the density of fungiform papillae. The fungiform papillae can be visualized by applying a vital stain (methylene blue) to the anterior portion of the tongue4
. Figure 2 compares the density of fungiform papillae between supertasters and non-tasters.
Figure 2. Difference of number of fungiform papillae between supertasters and non-tasters6
The fungiform papillae densities are different among three taster groups: non-tasters, medium tasters, and supertasters, and are highest in the supertasters8
. The density of fungiform papillae or the number of taste buds is directly correlated with the sensitivity of taste perception5
. A relationship between PROP taster status and number of fungiform papillae on the tongue were found4,5
. The fungiform papillae density has a significant correlation with perceived bitterness of PROP4,5
, sweetness of sucrose, and saltiness of NaCl5
Non-tasters are individuals with two homozygous recessive alleles (tt) and tasters are individuals with either heterozygous (one dominant allele and one recessive allele) or homozygous dominant allele (Tt, tT or TT)2,3,7
. Among the U.S. population, approximately 70% of the population are PROP tasters, while the remaining 30% are non-tasters8
. The medium tasters account for 50% and the supertasters account for 25% among the population2
. Females are more likely to be the supertasters than males because they have more fungiform papillae and have more taste pores than males1,2
. The percentage of taster status is varied among other ethnic populations. About 10% of Asians and 5% of Africans are PTC non-tasters9
. Supertasters are more sensitive to a wide range of oral stimuli including the bitter taste of caffeine and quinine, the sweet taste of sucrose and saccharin, and to the oral burn of capsaicin2,8
1 Bartoshuk, LM, Duffy, VB, and Miller, I.J. 1994. PTC/PROP tasting: anatomy, psychophysics and sex effects. Physiology and Behavior, 56, 1165-1171.
2 Bartoshuk, LM. 2000. Comparing sensory experiences across individuals: recent psychophysical advances illuminate genetic variation in taste perception. Chemical Senses, 25, 447-460.
3 Blakeslee, AF., and Salmon, MR. 1931. Odor and taste blindness. Eugenical News, 16, 105-110.
4 Duffy, VB, and Bartoshuk, LM. 2000. Food acceptance and genetic variation in taste. Journal of the American Dietetic Association, 100, 647-655.
5 Miller, IJ, and Reedy, FE. 1990. Variations in human taste bud density and taste intensity perception. Physiology and Behavior, 47, 1213-1219.
6 Murray, JA. 2004. Taste intensity and fungiform papillae. available online at http://faculty.uca.edu/~jmurray/baw2004/taste.pdf
7 Prescott, J, and Tepper, BJ. 2004. Genetic variation in taste sensitivity. New York: Marcel Dekker, Inc.
8 Tepper, BJ. 1999. Does genetic taste sensitivity to PROP influence food preferences and body weight? Appetite, 32, 422.
9 Yackinous, C., and Guinard, JX. 2001. Relation between PROP taster status and fat perception, touch, and olfaction. Physiology and Behavior, 72, 427-437.