6 n propyl 2 thiouracil

PROP taster status was assessed using a 3.2 mm PROP solution, prepared by dissolving 0.545 g/L of 6-n-propyl-2-thiouracil (Sigma-Aldrich, Burlington, MA, USA) into deionized water. Subjects rated the intensity of bitterness of two identical samples by using the generalized labelled magnitude scale (gLMS) [51 (link)]. Sample presentation and evaluation procedure were reported in Bartoshuk et al. [55 (link)]. PROP taster status of each subject was defined based on the average rating of the two replicates. Subjects were classified for responsiveness to PROP bitterness into three classes, applying previously used cut-off values [45 (link)], as follows: no-taster = NT (ratings on gLMS ≤ moderate, 17), medium-taster = MT (17 < ratings on gLMS < 53), and super-taster = ST (ratings on gLMS ≥ very strong, 53).

Flutamide (2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]-propanamide), glucose oxidase from Aspergillus niger (type II, 15,000–50,000 units/g solid), peroxidase from horseradish (type II, 150–250 units/mg solid), 6-N-propyl-2-thiouracil (PTU), N-acetyl-L-cysteine (NAC), (±)-6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox), 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPOL), N,N′-diphenyl-p-phenylenediamine (DPPD), resveratrol (3,5,4′-trihydroxy-trans-stilbene), and all other chemicals were purchased from Sigma-Aldrich Corp. (Oakville, ON, Canada). Type II collagenase (from Clostridium histolyticum) was purchased from Worthington Biochemical Corp. (Lakewood, NJ, USA). 4-(2-Hydroxyethyl) piperazine-1-ethanesulfonic acid (HEPES) was purchased from Boehringer-Mannheim Ltd. (Montreal, QC, Canada).

To assess individual responsiveness to chemosensory stimulation, seven aqueous solutions containing only one stimulus at a time were included in the study. The stimuli corresponded to the basic tastes (i.e., bitterness, sourness, sweetness, saltiness, and umami), the chemesthetic sensation of pungency, and the tactile sensation of astringency. The aqueous solutions were prepared to elicit an expected moderate/strong sensation on a general Labeled Magnitude Scale (gLMS) presented in vertical position [51 (link)]. The concentrations of the chemical reagents (European Pharmacopoeia Reference Standard Sigma-Aldrich, Milano, Italy) were as follows: citric acid, 4 g/kg (sourness); caffeine, 3 g/kg (bitterness); sucrose, 200 g/kg (sweetness); sodium chloride, 15 g/kg (saltiness); monosodium glutamate, 10 g/kg (umami); capsaicin, 1.5 mg/kg (pungent); and aluminium sulphate, 0.8 g/kg (astringency).
To assess participants’ PROP taster status, supra-threshold 3.2 mM PROP solution was prepared by dissolving 0.5447 g/L of 6-n-propyl-2-thiouracil (European Pharmacopoeia Reference Standard, Sigma-Aldrich, Milano, Italy) in deionized water in accordance with the PROP status assessment procedure described in [52 (link)].