Taste Perception of Sweet, Sour, Salty, Bitter, and Umami and Changes Due to l-Arginine Supplementation, as a Function of Genetic Ability to Taste 6-n-Propylthiouracil

Abstract

Behavioral reaction to different taste qualities affects nutritional status and health. 6-n-Propylthiouracil (PROP) tasting has been reported to be a marker of variation in taste perception, food preferences, and eating behavior, but results have been inconsistent. We showed that l-Arg can enhance the bitterness intensity of PROP, whilst others have demonstrated a suppression of the bitterness of quinine. Here, we analyze the taste perception of sweet, sour, salty, bitter, and umami and the modifications caused by l-Arg supplementation, as a function of PROP-taster status. Taste perception was assessed by testing the ability to recognize, and the responsiveness to, representative solutions of the five primary taste qualities, also when supplemented with l-Arg, in subjects classified as PROP-tasting. Super-tasters, who showed high papilla density, gave higher ratings to sucrose, citric acid, caffeine, and monosodium l-glutamate than non-tasters. l-Arg supplementation mainly modified sucrose perception, enhanced the umami taste, increased NaCl saltiness and caffeine bitterness only in tasters, and decreased citric acid sourness. Our findings confirm the role of PROP phenotype in the taste perception of sweet, sour, and bitter and show its role in umami. The results suggest that l-Arg could be used as a strategic tool to specifically modify taste responses related to eating behaviors.

Keywords: ">l-arginine; PROP taste status; taste perception.

Figure 1

Mean values ± SEM of the taste intensity evoked by stimulation with two concentrations (low, L and high, H) of each stimulus (sucrose, 20 and 146 mmol/L; NaCl, 20 and 85 mmol/L; citric acid, 1.3 and 5.2 mmol/L; caffeine, 1.5 and 6.7 mmol/L; MSG, 10 and 80 mmol/L) (a). n = 64. The same data shown according to PROP-taster status of subjects (b), which was determined by the three-solution test [71] and the impregnated paper screening test [72]. Super-taster (n = 9, all with PAV/PAV genotype of TAS2R38 locus), medium-taster (n = 35 of which 31 had PAV/AVI and four AVI/AVI genotype), non-taster (n = 20, all with AVI/AVI genotype). * Significant difference with respect to the corresponding value of the stimulus at low concentration (p < 0.00011; Fisher’s LSD test, subsequent repeated-measures ANOVA). For each solution, different letters on top of bars (a, b or c) indicate significant difference (p ≤ 0.05; Fisher’s LSD test; subsequent one-way ANOVA).

Figure 2

The number of subjects who perceived no taste, correctly recognized the taste, or described an incorrect taste response (Other) for the stimulus representative of each primary taste quality, presented at low concentration or supplemented with l-Arg (1:1 molar ratio l-Arg). n = 64. (a) Sucrose 20 mmol/L; (b) NaCl 20 mmol/L; (c) Citric acid 1.3 mmol/L; (d) Caffeine 1.5 mmol/L; and (e) MSG 10 mmol/L. * Significant difference (p < 0.00001; Fisher’s exact).

Figure 3

Mean values (± SEM) of taste intensity evoked by stimulation with the sucrose (20 mmol/L), NaCl (20 mmol/L), citric acid (1.3 mmol/L), caffeine (1.5 mmol/L) and MSG (10 mmol/L) and those evoked by stimulation with the same solutions supplemented with l-Arg (1:1 molar ratio) according to PROP-taster status of subjects, which was determined by the three-solution test [71] and the impregnated paper screening test [72]. (a) Sucrose: n = 21; (b) NaCl: n = 37; (c) Citric Acid: n = 46; (d) Caffeine: n = 59; and (e) MSG: n = 60. * Significant difference (p < 0.037; Fisher’s LSD test, subsequent repeated-measures ANOVA). ^§ Significant difference with respect to the corresponding value of each PROP-taster group in response to each stimulus without l-Arg supplementation (p < 0.037; Fisher’s LSD test, subsequent repeated measures ANOVA).

Figure 4

Mean values ± SEM of density of fungiform papillae (n/cm²) on the anterior part of the tongue in super-tasters (n = 9, all with PAV/PAV genotype of TAS2R38 locus), medium-tasters (n = 35 of which 31 had PAV/AVI and 4 AVI/AVI genotype), and non-tasters (n = 20, all with AVI/AVI genotype). Different letters indicate significant difference (p ≤ 0.0006; Fisher’s LSD test; subsequent one-way ANOVA).