The relationship between phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP) taster status and taste thresholds for sucrose and quinine
Introduction
Phenylthiocarbamide (PTC) and its chemically related compound, 6-n-propylthiouracil (PROP), provide an extremely bitter taste to some subjects (tasters) but are tasteless or only slightly bitter to others (nontasters).1, 2, 3, 4 Although approximately 15–30% of people are known to be nontasters genetically,5, 6 the taster/nontaster frequency differs among ethnic groups.7, 8, 9, 10 Noting that the taster group showed much variability in taste threshold, it was proposed that sub-populations of ‘supertasters’ and ‘medium-tasters’ might exist. Supertasters were distinguished from medium-tasters by their elevated ratio of perceived bitterness of above-threshold PROP solutions relative to the perceived saltiness of NaCl solutions.11 Tasters, especially supertasters, may have a reduced dietary exposure to bitter but beneficial phytonutrients found in vegetables and fruits.12, 13 Therefore, screening for PTC and/or PROP (PTC/PROP) taster status may have a public health importance.14, 15
The PTC/PROP perception has been known to correlate with the taste perception of various primary taste qualities,16, 17 especially bitter and sweet tastes.18, 19, 20, 21 However, these previous results on the relationship of PTC/PROP perception with perception of taste quality were based on food aversions and taste intensities, not on threshold tests, which are the most widely used quantitative taste tests. Of the available quantitative threshold tests, a taste detection threshold test establishes the lowest concentration at which a substance can be distinguished from water. In contrast, a taste recognition threshold test determines the lowest concentration at which the taste quality of a substance can be identified.22
The aim of this study was to investigate whether or not the PTC/PROP taster status is related to the taste detection and recognition thresholds for sucrose and quinine in the young adult population.
Section snippets
Participants
Sixty-nine subjects (35 men and 34 women; mean age, 23.9 ± 1.2 years), who were students of the School of Dentistry at Seoul National University, were enrolled in the study. All of them were nonsmokers. A questionnaire, which included questions regarding chronic sinusitis, chronic obstructive pulmonary disease, diabetes, psychological disorders, loss of olfactory sense, history of ear surgery or tonsillectomy and dry mouth, was used to select the subjects. The subjects did not show any positive
Results
As shown in Table 1 and Fig. 1, the percentages of nontasters, medium-tasters and supertasters were 13, 70 and 17%, respectively. Taster/nontaster status determined using the PTC was exactly in accordance with that found using the PROP (data not shown).
The detection and recognition thresholds for sucrose and quinine HCl in all subjects are shown in Table 2. Although each detection and recognition threshold was higher in men than in women, there was no significant difference.
As shown in Table 3,
Discussion
The percentage of nontasters among Korean young adults was found to be 13% in this investigation and 20% in a previous study.10 These numbers are higher than those found in American Indians, and lower than those observed in European and American Caucasians.7, 9 The percentage of supertasters was 17% in this study, which was lower than the results of previous studies reporting 21–30% of supertasters.11, 13, 31, 32, 33, 34, 35 This is likely explained by a combination of factors, such as ethnic
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