PROP Non-tasters Research Articles

Evaluation of the Long-Lasting Flavour Perception after the Consumption of Wines Treated with Different Types of Oenological Additives Considering Individual 6-n-Propylthiouracil Taster Status.

Due to the limited scientific knowledge on the impact of commercial oenological additives on flavour perception, the aim of this work was to evaluate the effect of different types of oenological additives on the long-lasting flavour perception (flavour persistence) during wine tasting, also considering the effect of the individual PROP (6-n-propylthiouracil) taster status (PTS). To do so, white and red wines with two oenotannins (ellagitannin and gallotannin) and a commercial yeast mannoprotein were prepared. A control wine of each type was also made without additives. All the wines were spiked with a mixture of aromatic compounds responsible for the "fruity" and "woody" notes. Retronasal aroma and astringency were evaluated at the same time using time-intensity (TI) methodology and a trained panel (n = 40), including PROP non-tasters (NTs) and tasters (Ts). The results showed a significant effect of PTS on the long-lasting perception of astringency, being Ts who showed higher values than NTs for most TI parameters. However, PTS did not affect aroma persistence. In addition, the three oenological additives had an effect on astringency and retronasal aroma perception. They significantly increased the long-lasting perception of astringency compared to the control, while gallotannin also increased the persistence of the woody aroma.

The influence of PROP taster status on habitual sweet food consumption and dietary intake amongst obese and non-obese adults

Introduction: Ability to taste 6-n-propylthiouracil (PROP) predicts both taste sensitivity and food preferences, with PROP tasters being more sensitive to sweet taste in foods, which may lead to less intake of sugary foods. However, when obesity progresses, the individual’s sense of taste and eating patterns may change. The aim of this study was to evaluate if PROP taster status affected habitual sweet food consumption and nutritional intake in obese and non-obese people. Methods: A total of 88 obese and 92 non-obese Malay male and female participants aged 20-45 years were classified into PROP non-tasters, medium tasters, or supertasters by using PROP filter paper screening procedure. Sweet food consumption was assessed using food frequency questionnaire (FFQ), while dietary intake was measured by using 3-day food diary. Data were analysed using General Linear Model (GLM) Analysis of Covariance (ANCOVA) to compare for differences and associations among variables. Results: Overall, there was no significant association between body mass index groups and PROP taster status (p>0.05). No significant differences were found on any habitual sweet food intake and dietary intake according to PROP taster status in both obese and non-obese participants (p>0.05). However, there was a significant difference (p<0.05) in fruit intake according to PROP taster status among obese participants. Conclusion: The findings suggest that PROP taster status does not play a role in nutrient intakes among obese and non-obese individuals

Self-Rated Aversion to Taste Qualities and the PROP Taster Phenotype Associate with Alcoholic Beverage Intake and Preference

Consumers often identify “taste” as an important factor when selecting alcoholic beverages. Although it is assumed that reduced alcohol consumption in PROP super-tasters is due to a greater dislike of the nominally aversive sensations that they experience more intensely (e.g., bitterness) when compared to PROP non-tasters, this question has not been specifically asked to them. Therefore, we examined consumers’ self-reported aversion towards specific sensory attributes (bitter, hot/burn, dry, sour, sweet, carbonation) for four alcoholic beverage types (white wine, red wine, beer, spirits) using a convenience sample of U.S. wine consumers (n = 925). Participants rated 18 statements describing different combinations of sensory attributes and alcoholic beverages on a 5-point Likert scale (e.g., Beer tastes too bitter for me). Individuals who tended to agree more strongly with the statements (i.e., they were more averse; p(F) < 0.05) tended to (i) consume less of all beverage types, (ii) consume a higher proportion of white wine (p(r) < 0.05), and (iii) were more likely to be female or PROP super-tasters. The results suggest that self-reported aversion to specific sensory attributes is associated with not only lower overall intake of alcoholic beverages, but also a shift in the relative proportions of beverage type consumed; a key finding for studies investigating how taste perception impacts alcohol consumption.

Role of taste perception in white spot lesion formation during orthodontic treatment.

To investigate the role of individual's taste sensitivity using 6-n-propylthiouracil (PROP) in the development of white spot lesions (WSLs) in adolescent orthodontic patients. 44 healthy adolescents, aged 12 to 16 years old, who were in fixed-appliance orthodontic treatment for at least 6 months, consented to participate in this cross-sectional study. Data regarding participants' demographic information, oral hygiene practices, and dietary habits were obtained by a questionnaire. An oral clinical examination was performed to determine the oral hygiene status, the presence of WSLs and dental caries experience. The taste phenotype of the participants was evaluated through PROP test and they were accordingly divided into PROP nontasters and PROP tasters. The sample consisted of 24 subjects in the WSL group and 20 subjects in the WSL-free group. The WSL group demonstrated higher mean plaque score (48.2), mean decayed, missing, and filled surfaces (2.38), and mean decayed, missing, and filled teeth (1.96) scores compared to the WSL-free group (38.7, 0.85, and 0.55, respectively), but no significant differences were found. Most subjects in the WSL group were PROP nontasters (66.6%) whereas most subjects in the WSL-free group were PROP tasters (75%); a significant difference was observed between the groups (P = .006). The prevalence of white spot lesions was significantly higher in adolescent orthodontic patients who were PROP nontasters compared to PROP tasters. A PROP taste perception could be a potential risk factor for the formation of WSLs during fixed orthodontic treatment that warrants further attention.

A bitter taste in the mouth: The role of 6-n-propylthiouracil taster status and sex in food disgust sensitivity

We investigated the relationship between perceived bitterness, food disgust sensitivity, and sex. Participants completed the 8-item Food Disgust Scale and a 6-n-propylthiouracil (PROP) taster test and were categorised as PROP non-tasters, medium-tasters, or supertasters. An analysis of variance of between-subject factors sex and PROP taster status was conducted with disgust sensitivity as the dependent variable. We found a significant interaction of sex and PROP taster status on disgust sensitivity and an association between disgust sensitivity and PROP taster status in males but not in females. Our study provided new evidence on sex differences in food disgust and PROP taste sensitivity.

Perception and liking of soups flavored with chipotle chili and ginger extracts: Effects of PROP taster status, personality traits and emotions

Individual differences in perception and liking of spicy foods are well known, but poorly understood. Most studies have investigated this phenomenon using chili pepper (capsaicin), while neglecting other pungent spices. This study examined the role of PROP taster status (a genetic marker for oral sensations), personality factors, and emotions in perception and liking of tomato and butternut squash soups flavored with chipotle chili and ginger extracts, respectively. Each extract was added at three concentrations: low, medium and high. Overall, the chili extract had a greater influence on the sensory profile and emotional ratings of the tomato soup than the ginger extract on the squash soup. Specifically, PROP non-tasters liked the burn of the tomato soup at the high chili extract concentration more than the other taster groups, high sensation seekers liked the burn from the low and high chili extract concentrations more than low sensation seekers, and emotional ratings for ‘disgust’, ‘mouthwatering’, and ‘relaxed’ were altered after soup tastings. Predictors of overall liking also differed between the soups; burn intensity, ‘disgust’ and the PROP x ‘disgust’ interaction predicted liking of the chili tomato soup, whereas ginger flavor, overall flavor, ‘disgust’ and ‘wellbeing’ predicted overall liking of the ginger squash soup. These data suggest that: 1) PROP status and sensation seeking influenced responses to chili pepper but not ginger flavored soups and 2) different emotions predicted overall liking of the soups, though ‘disgust’ was a negative predictor for both. Further exploration into the role of emotions on preferences for pungent spices is warranted.

An automated system for the objective evaluation of human gustatory sensitivity using tongue biopotential recordings.

The goal of this work is to develop an automatic system for the evaluation of the gustatory sensitivity of patients using an electrophysiological recording of the response of bud cells to taste stimuli. In particular, the study aims to evaluate the effectiveness and limitations of supervised classifiers in the discrimination between subjects belonging to the three 6-n-propylthiouracil (PROP) taster categories (supertasters, medium tasters, and non-tasters), exploiting features extracted from electrophysiological recordings of the tongue. Thirty-nine subjects (equally divided into the three PROP status classes by standard non-objective scaling methods) underwent a non-invasive, differential, biopotential recording of their tongues during stimulation with PROP by using a custom-made, flexible, silver electrode. Two different classifiers were trained to recognize up to seven different features extracted from the recorded depolarization signal. The classification results indicate that the identified set of features allows to distinguish between PROP tasters and non-tasters (average accuracy of 80% ± 18% and up to 94% ± 15% when only supertasters and non-tasters are considered), but medium tasters were difficult to identify. However, these apparent classification errors are related to uncertainty in the labeling procedures, which are based on non-objective tests, in which the subjects provided borderline evaluations. Thus, using the proposed method, it is possible, for the first time, to automatically achieve objective PROP taster status identification with high accuracy. The simplicity of the recording technique allows for easy reproduction of the experimental setting; thus the technique can be used in future studies to evaluate other gustatory stimuli. The proposed approach represents the first objective and automatic method to directly measure human gustatory responses and a milestone for physiological taste studies, with applications ranging from basic science to food tasting evaluations.

Understanding the role of personality and alexithymia in food preferences and PROP taste perception

Taste perception and food preferences are influenced by a variety of factors, including personality characteristics. The aims of this study were to examine the role of personality characteristics, such as alexithymia (a personality construct characterized by inability to identify, describe, and work with one's own feelings), in: 1) taste responses to the bitter genetic taste-marker PROP and 2) food liking. We studied 649 healthy subjects residing in six genetically-isolated villages of Northeast Italy. Data on PROP taste responsiveness, food liking, personality characteristics and TAS2R28 genotypes were collected.Results showed that PROP non-tasters had higher alexithymia scores than PROP tasters. Moreover, the presence of alexithymia in heterozygous individuals for the rs1726886 polymorphism of the TAS2R38 gene was associated with a reduction in the perceived intensity of PROP.Finally, higher alexithymia scores were associated with liking of alcohol, sweets and fats/meats whereas lower alexithymia scores were related to liking of vegetables, condiments and strong cheeses, Measures of temperament, character, anxiety and depression were also related to food liking.Our findings suggest that: 1) alexithymia, in addition to the TAS2R38 polymorphism, may play a role in responsiveness to the aversive and bitter taste of PROP; and 2) alexithymia, in combination with other personality traits, may provide important insights for better understanding food liking.

Relationship of 6‐n‐Propylthiouracil (PROP) Taste Sensitivity to Alcohol and Caffeine Intakes among Ethnically Diverse College Students

BackgroundIt has been suggested that greater taste sensitivity to 6‐n‐propylthiouracil (PROP) influences the oral sensation of alcohol and caffeine and serves as a deterrent to alcohol and caffeine consumption.ObjectiveThis study was conducted to examine the relationship of PROP taste sensitivity to alcohol and caffeine intakes among ethnically diverse college students.MethodsThe sample included 360 college students (164 males; 72 African Americans, 80 Caucasians, 73 Hispanics, 135 Asians; Age: Mean±SE=23.4±0.3yr) living in the New York City area. Subjects were classified as PROP non‐tasters and tasters using the PROP filter paper method and the general Labeled Magnitude scale. Their daily alcohol and caffeine intakes were assessed using a Food Frequency Questionnaire.ResultsThe proportion of PROP non‐tasters in this study was 29%. PROP non‐tasters had significantly higher daily alcohol intake (Mean±SE, 3.8±0.6 vs. 2.2±0.2 [g]; P=0.007) and caffeine intake(116.5±9.9 vs. 83.1±5.4 [mg];P=0.002) than did PROP non‐tasters. Male subjects had significantly higher alcohol (P=0.05) and caffeine intakes (P=0.03) compared with female subjects. Finally, Caucasian subjects had significantly higher alcohol (P<0.001) and caffeine intakes (P=0.002) than did any other ethnic groups. The multiple regression results showed that ethnicity, PROP status, and caffeine intake significantly predicted alcohol intake.ConclusionThis study suggests that PROP status is significantly associated with alcohol and caffeine intakes. Future studies should examine how cultural norms interact with PROP status. FundingThis study was supported by PSC‐CUNY grant (#65362‐00‐43) from the Research Foundation of the City University of New York.

Relationships of PROP Taste Phenotype, Taste Receptor Genotype, and Oral Nicotine Replacement Use.

Recommended dosage of oral nicotine replacement therapy (NRT) product is often not achieved in smoking cessation attempts. n-6-propylthiouracil (PROP) bitter taste phenotype may be a potential risk factor for non-adherence to oral NRT products due to their bitter taste. There is limited literature on this phenotype in the context of smoking and none in relation to oral NRT pharmacotherapy. The association of PROP taste phenotype with NRT usage and sensory response to products was examined. In a cross-over experimental design, 120 participants received a 1 week supply of nicotine inhalers and 1 week of nicotine lozenges with random assignment to order. Mixed effects linear model analyses were conducted. PROP taste phenotype and taste receptor genotype were not associated with NRT usage or sensory response to NRT, after adjusting for other factors. However, PROP non-tasters used a higher number of lozenges per day (continuous exposure) than nicotine cartridges (intermittent exposure). Unexpectedly, half of baseline PROP non-tasters shifted to taster phenotype 2 weeks after smoking cessation or reduction. Menthol cigarette smokers identified higher NRT strength of sensation scores than nonmenthol smokers. Taste receptor genotype was related to PROP taste phenotype (Kendall τ = .591, p = .0001). A nonsignificant relationship of PROP phenotype and NRT usage may be associated with NRT under-dosing and limited variance in the outcome variable. PROP non-tasters' greater use of lozenges is consistent with nicotine exposure being less aversive to non-tasters. Further research of this and other factors impacting NRT usage are warranted to effectively inform smoking cessation pharmacotherapy.

Relationship among prop phenotype, body mass index, waist circumference, total body fat and food intake

The PROP phenotype (6-n-propylthiouracil) has been proposed as indicator of body mass index, adiposity and food intake. This relationship among variables is contradictory. No correlation has been found among the PROP phenotype, body indicators and energy consumption in some studies. The aim of this study was to determine the relationship among PROP taster status, body mass index (BMI), waist circumference (WC), total body fat (TBF) and food intake. The PROP taster status was established using two scales: the nine-point scale and the general labeled magnitude scale. Dietary habits of participants were recorded online during 35 days. The classification by PROP phenotype varied according to the scale. No significant differences were observed between PROP tasters and PROP non-tasters, with both scales, in body mass index, waist circumference, total body fat and energy and macronutrient intake. The PROP phenotype was not an indicator factor of body weight, adiposity and energy and macronutrients consumption in young adults.

Taste sensitivity to 6-n-propylthiouracil is associated with endocannabinoid plasma levels in normal-weight individuals

ObjectiveA decreased sensitivity to 6-n-propylthiouracil (PROP) has been shown to be associated with increased energy intake and therefore an increased body mass index, although other studies have not confirmed this association, suggesting the involvement of other factors. We investigated whether the endocannabinoid system, which also modulates hunger/satiety and energy balance, plays a role in modulating eating behavior influenced by a sensitivity to PROP. MethodsThe plasma profile of the endocannabinoids 2-arachidonoylglycerol (2-AG), anandamide (AEA), and congeners of AEA, palmitoylethanolamide and oleylethanolamide (OEA), was determined in normal-weight PROP supertasters (STs) and PROP non-tasters (NTs). A cognitive eating behavior disorder was assessed by the Three-Factor Eating Questionnaire, which estimates dietary restraint, disinhibition, and perceived hunger. ResultsThe disinhibition score of NTs was higher than those of STs (P = 0.02). Moreover, in NTs, OEA was inversely correlated to the perceived hunger score (r = −0.7, P = 0.002), and AEA was positively correlated to the restraint score (r = 0.5, P = 0.04) and negatively to the perceived hunger score, although the latter correlation was at the limit of statistical significance (r = −0.47, P = 0.05). In addition, we found lower concentrations of AEA and 2-AG in the plasma of NT compared with ST subjects (AEA, P = 0.034; 2-AG, P = 0.003). ConclusionsOur data suggest that a higher disinhibition behavior in NTs may be compensated in part, in normal-weight subjects, by the decrease of peripheral endocannabinoids to downregulate the hunger–energy intake circuitry.

PROP taster status interacts with the built environment to influence children's food acceptance and body weight status

Eating behaviors and obesity are complex phenotypes influenced by genes and access to foods in the environment, but few studies have investigated the interaction of these two variables. The purpose of this study was to use a gene-environment interaction model to test for differences in children's food acceptance and body weights. Inherited ability to taste 6-n-propylthiouracil (PROP) was assessed as a marker of oral taste responsiveness. Food environment was classified as “healthy” or “unhealthy” based on proximity to outlets that sell fruits/vegetables and fast foods using Geographic Information Systems (GIS). The cohort consisted of 120 children, ages 4–6 years, recruited from New York City over 2005–2010. Home address and other demographic variables were reported by parents and PROP status, food acceptance, and anthropometrics were assessed in the laboratory. Based on a screening test, children were classified as PROP tasters or non-tasters. Hierarchical linear models analysis of variance was performed to examine differences in food acceptance and body mass index (BMI) z-scores as a function of PROP status, the food environment (“healthy” vs. “unhealthy”), and their interaction. Results showed an interaction between taster status and the food environment on BMI z-score and food acceptance. Non-taster children living in healthy food environments had greater acceptance of vegetables than taster children living in healthy food environments (p≤0.005). Moreover, non-tasters from unhealthy food environments had higher BMI z-scores than all other groups (p≤0.005). Incorporating genetic markers of taste into studies that assess the built environment may improve the ability of these measures to predict risk for obesity and eating behaviors.

The examination of fatty acid taste with edible strips

The objective of this study was to determine whether humans could detect long-chain fatty acids when these lipid molecules are delivered to the oral cavity by edible taste strips. For suprathreshold studies, up to 1.7μmol of stearic acid or linoleic acid was incorporated into 0.03mm thick, one-inch square taste strips. Normalized taste intensity values for stearic acid were in the barely detectable range, with values equal to, or slightly above control strips. One-third of test subjects described the taste quality as oily/fatty/waxy. Approximately 75% of test subjects could detect the presence of linoleic acid when this fatty acid was incorporated into dissolvable strips. Normalized taste intensity values for linoleic acid were in the weak to moderate range. The most commonly reported taste quality responses for linoleic acid were fatty/oily/waxy, or bitter. When nasal airflow was obstructed, the perceived taste intensity of linoleic acid decreased by approximately 40%. Taste intensity values and taste quality responses for linoleic acid were then compared among tasters and non-tasters of 6-n-propylthiouracil (PROP). Individuals who could detect the bitter taste of PROP reported higher taste intensity values for linoleic acid compared with PROP non-tasters. However, taste quality responses for linoleic acid were similar among both PROP tasters and PROP non-tasters. These results indicate that humans can detect long-chain fatty acids by both olfactory and non-olfactory pathways when these hydrophobic molecules are delivered to the oral cavity by means of edible taste strips. These studies further show that genetic variation in taste sensitivity to PROP affects chemosensory responses to the cis-unsaturated fatty acid (linoleic acid) in the oral cavity.

The Relation between 6-n-Propylthiouracil Sensitivity and Caries Activity in Schoolchildren

Caries activity tests are being used to assess caries risk in children. In recent years the purpose of most studies has been to develop practical, quick, reliable and economic tests. Clinical studies showed that the difference in sensitivity to the bitter taste of 6-n-propylthiouracil (PROP) is a heritable trait and may influence children’s nutritional habits and caries development. The aim of this study was to investigate the relation between PROP sensitivity and caries activity in schoolchildren, in comparison with different caries activity tests. One hundred and twenty children aged between 7 and 12 years (mean age 9.97 ± 1.59) were investigated to determine socioeconomic status and oral hygiene habits, fluoride consumption, DMFT, DMFS, df, dfs, plaque indexes, and nutritional habits. Children were divided into three groups according to their caries risk status based on the Cariogram. The solution test and the PROP-impregnated filter paper test were used together to determine PROP sensitivity. After all associated factors had been controlled, stepwise regression analyses revealed that DMFT and dfs scores were important determinants of PROP. According to dfs, the sensitivity of the Cariogram and of PROP tests was 0.85 and 0.70, respectively, and specificity was 0.32 and 0.33, respectively. There was an inverse significant relationship between PROP sensitivity and DMFT, DMFS, and dfs results (p < 0.01). In conclusion, PROP nontasters were significantly more likely to have high caries risk than PROP tasters (p < 0.01).

Relationship of intake of plant-based foods with 6-n-propylthiouracil sensitivity and food neophobia in Japanese preschool children

Diets rich in plant-based foods such as vegetables, fruits and soy foods have been suggested to have beneficial effects on health. However, phytochemicals contained in plant-based foods are generally bitter and acrid. We investigated whether intake of vegetables, fruits and soy foods is associated with sensitivity to bitterness and reluctance to eat new foods (food neophobia) in Japanese preschool children. Subjects of this cross-sectional study were healthy Japanese, 167 boys and 156 girls, aged 4-6 years. Intake of vegetables, fruits and soy foods was estimated from 3-day dietary records. Subjects were classified as either tasters or non-tasters of 6-n-propylthiouracil (PROP) based on their ability to taste 0.56 mmol/l PROP. Information on each child's age, height, weight, food neophobia status and food variety, as well as maternal diet and parental control over the child's eating, was obtained by a parent-administered questionnaire. Food neophobia was assessed using the Child Food Neophobia Scale (CFNS). A high intake of vegetables was significantly associated with a low CFNS score in boys after controlling for covariates (P=0.0008). Among the boys, soy food intake was significantly higher in PROP non-tasters than in tasters, except those with low CFNS scores (P=0.0019). High intake of soy foods was significantly associated with a low neophobia score in PROP tasters but not in non-tasters (P=0.0024). These data suggest that sensitivity to bitter taste and food neophobia may influence the consumption of vegetables and soy foods among Japanese preschool boys.

Polymorphisms in TAS2R38 and the taste bud trophic factor, gustin gene co-operate in modulating PROP taste phenotype

The PROP taste phenotype varies greatly among individuals, influencing eating behavior and therefore may play a role in body composition. This variation is associated with polymorphisms in the bitter receptor gene TAS2R38 and the taste-bud trophic factor gustin gene. The aim of this study was to examine the relationship between TAS2R38 haplotypes and the gustin gene polymorphism rs2274333 in modulating PROP taste phenotype. PROP phenotype was determined in seventy-six volunteers (29 males, 47 females, age 25±3y) by scaling methods and threshold measurements. TAS2R38 and gustin gene genotyping was performed using PCR techniques. The lowest responsiveness in PROP nontasters is strongly associated with the AVI nontasting TAS2R38 variant and the highest responsiveness in supertasters is strongly associated to allele A and genotype AA of the gustin gene. These data support the hypothesis that the greater sensitivity of supertasters could be mediated by a greater taste-bud density. Polymorphisms in TAS2R38 and gustin gene, together, accounted for up to 60% of the phenotypic variance in PROP bitterness and to 40% in threshold values. These data, suggest that other unidentified factors may be more relevant for detecting low concentrations of PROP. Moreover, the presence of the PAV variant receptor may be important for detecting high concentrations of PROP, whereas the presence of allele A in gustin polymorphism may be relevant for perceiving low concentrations. These data show how the combination of the TAS2R38 and gustin gene genotypes modulate PROP phenotype, providing an additional tool for the evaluation of human eating behavior and nutritional status.

Validation of edible taste strips for identifying PROP taste recognition thresholds

The purpose of this study was to validate the use of edible taste strips for measuring taste recognition thresholds for the bitter-tasting compound 6-n-propylthiouracil (PROP). Taste recognition thresholds for PROP were obtained by two separate methods. Thresholds were also identified in subjects whose airflow through the nose was blocked. Threshold values were then compared to genotype analysis of the TAS2R38 taste receptor, which is the major determinant for the detection of PROP. Edible taste strips were used to examine taste recognition thresholds for PROP. Thresholds were determined by the method of ascending limits and by the method of reversals. Single nucleotide polymorphism analysis of the TAS2R38 gene was used to identify PROP taster status. Taste recognition thresholds for PROP formed two distributions. Thresholds for one group varied from 4 to 219 nmol and represented PROP tasters. The second group could not detect the bitter taste of PROP at ≤800 nmol and represented PROP nontasters. The method of ascending limits and the method of reversals yielded similar threshold results. The expression of a PAV allele permitted detection of PROP, but AVI homozygotes could not detect the bitter taste of PROP. Edible taste strips were successfully used to detect PROP thresholds at values equal to or lower than those obtained in previous studies using PROP solutions or PROP-impregnated filter papers. This study provides validity evidence for the use of edible taste strips for identifying PROP in the human population.

Sensitivity to 6-n-propylthiouracil is associated with gustin (carbonic anhydrase VI) gene polymorphism, salivary zinc, and body mass index in humans

The individual ability to taste 6-n-propylthiouracil (PROP) may be correlated with body mass index (BMI) and differences in the salivary proteins involved in taste function, such as the zinc-dependent enzyme gustin, which is a trophic factor of taste buds. We investigated the possible association of PROP taste responsiveness with gustin gene polymorphism rs2274333 (A/G), salivary ionic zinc concentrations, and BMI. We measured cognitive eating behaviors and BMI in 75 volunteers (28 men and 47 women; mean plusmn SEM age: 25 plusmn 3 y). The intensity of taste perception evoked by PROP and sodium chloride solutions was estimated to evaluate PROP taster status. Salivary ionic zinc concentrations were measured, and molecular analyses of the gustin gene polymorphism were performed in individuals classified by PROP status by using polymerase chain reaction techniques. We classified subjects as PROP supertasters (n = 27), medium tasters (n = 28), or nontasters (n = 20). Salivary ionic zinc concentrations and BMI were greater in nontasters than in supertasters (P = 0.003 and P = 0.042, respectively). Molecular analyses of gustin DNA showed that allele A and genotype AA were significantly more frequent in supertasters, whereas allele G and genotype GG were significantly more frequent in nontasters (P lt 0.001). These data showed that responsiveness to PROP is inversely related to BMI and salivary ionic zinc concentrations. The gustin gene dimorphism rs2274333 observed in supertaster and nontaster subjects may influence the protein conformation and, thereby, affect zinc ion binding. Our data showed a direct association between PROP sensitivity and a polymorphism in the gustin gene that is hypothesized to affect its function. This trial was registered at clinicaltrials.gov as UNICADBSITB-1.

Individual Differences in Prefrontal Cortex Activity during Perception of Bitter Taste Using fNIRS Methodology

Although bitter taste has a crucial role in nutrition by preventing the ingestion of toxic foods, there are few studies on bitter taste neuroimaging. To identify cortical areas involved in bitter taste perception and to determine if individual differences in taste sensitivity to 6-n-propylthiouracil (PROP) are represented in the brain by different cortical activation patterns, we examined 48 healthy volunteers using functional near-infrared spectroscopy. Participants rated the perceived intensity of filter paper disks impregnated with PROP and NaCl during the imaging procedure and were then classified as PROP tasters and nontasters. We monitored cortical activity in both the anterior and posterior regions of the dorsolateral prefrontal cortex (DLPFC) and in the ventrolateral prefrontal cortex (VLPFC). No activity was detected in the anterior DLPFC in any of the participants. However, during the administration of PROP, significant cortical activation was detected in the more posterior regions of the left DLPFC and in the left and right VLPFC but only in PROP tasters. PROP nontasters showed no cortical activity in these areas. These data suggest that the prefrontal cortex is involved in the conscious perception of the bitter taste of PROP and that the pattern of activity is consistent with individual differences in the ability to taste this compound. Thus, the PROP phenotype is associated with fundamental differences in cortical taste processing.