Exploring associations between taste perception, oral anatomy and polymorphisms in the carbonic anhydrase (gustin) gene CA6

The gustin gene variation at rs2274333 and PROP taster status affect dietary fat perception: a stepwise multiple regression model study

Gustin, a trophic factor for taste bud development, and its polymorphism at rs2274333 influence taste perception of 6-n-propylthiouracil (PROP) and fungiform papillae (FP) density. The PROP taster status affects dietary fat sensing and body composition. However, there is a paucity of research on the gustin genotype with dietary fat perception, PROP tasting ability, and body mass index (BMI). Thus, taste sensitivity to fat and bitterness was evaluated in 178 healthy individuals. The general labeled magnitude scale was used to determine suprathreshold taste intensity ratings, whereas the alternative forced choice approach was used to estimate the taste-sensing ability. The FP density was assessed by applying blue-colored food dye over the anterior region of the tongue. Restriction fragment length polymorphism was used to detect the genetic polymorphism (rs2274333) in the carbonic anhydrase VI (CA-VI) gene. Fisher's chi-square analysis showed that the CA-VI genotype and allelic frequencies significantly correlated (p<0.001) with the PROP taster status and BMI. Healthy individuals with AA genotypes of the CA-VI polymorphism and PROP super-tasters demonstrated stronger gustatory sensitivity for linoleic acid (LA) with greater FP density in comparison to individuals with AG/GG genotypes and other PROP taster groups. Stepwise forward multiple regression analysis indicates that BMI and PROP taster status significantly influence the LA sensing ability. The suprathreshold intensity rating for LA was also significantly impacted by PROP taster status and CA-VI genotypes, with a variation of 73.3%. Overall, our findings show a relationship between the taste papillae environment and the CA-VI genetic mutation at rs2274333, which influenced the gustatory preference for dietary fat and bitter taste.

Association of the bitter taste genes TAS2R38 and CA6 and breast cancer risk; a case-control study of Polish women in Poland and Polish immigrants in USA

It is known that the perception of bitterness is mediated by type 2 bitter taste receptors (TAS2Rs). However, recent reports have suggested that the carbonic anhydrase 6 (CA6) gene may also influence bitterness sensing. Genetic variants in these genes could influence dietary intake of brassica vegetables, whose increased consumption has been observed in the literature, though inconsistently, to decrease breast cancer (BC) risk. We hypothesized that the estimated odds ratios (ORs) for the association between BC and taster diplotype (PAV/PAV) and/or genotype A/A, will be in the direction of increased BC risk, potentially due to reduced consumption of brassica vegetables. Using a case-control study of BC in Polish women in Poland (210 cases and 262 controls) and Polish immigrant women to USA (78 cases and 170 controls) we evaluated the association of the taster diplotypes in TAS2R38 gene and genotypes in the CA6 gene and BC risk in these two populations individually and jointly. No significant increase in risk was observed for the TAS2R38 PAV/PAV diplotype (tasters) in each population individually or in the joint population. For the CA6 gene, in the joint population, we observed an increased BC risk for the combined G/A and G/G genotypes (non-tasters) vs A/A (tasters), OR = 1.41 (95% CI 1.04-1.90, p = 0.026) which after adjustment for False Discovery Rate (FDR), was not significant at p≤0.05 level. However, for the joint population and for the combined genotype of the two genes AVI/AVI+G* (non-tasters) vs. PAV/*+A/A (tasters), we observed a significant increase in BC risk, OR = 1.77 (95%CI 1.47-2.74, p = 0.01), for the non-tasters, which remained significant after FDR adjustment. In conclusion for the joint population and the joint effect for the two bitter sensing genes, we observed an increase in BC risk for the bitterness non-tasters, association which is in the opposite direction to our original hypothesis.

Gene Methylation Affects Salivary Levels of the Taste Buds' Trophic Factor, Gustin Protein

The salivary protein, Gustin/carbonic anhydrase VI, has been described as a trophic factor responsible for the growth of taste buds. We found, in a genetically homogeneous population, that the polymorphism rs2274333 (A/G) of the Gustin gene is crucial for the full functionality of the protein and is associated with taste sensitivity. However, other studies have failed to find this evidence. Here, we verified if Gustin gene methylation can affect the salivary levels of the protein, also concerning the polymorphism rs2274333 and PROP bitter responsiveness. The Gustin gene methylation profiling and the quantification of the Gustin salivary levels were determined in sixty-six volunteers genotyped for the polymorphism rs2274333 (A/G) (Ser90Gly in the protein sequence). The fungiform papillae density was also determined. The results confirm our earlier observations by showing that AA genotypes had a greater density of fungiform taste papillae, whereas the GG genotypes showed a lower density. We also found variations in the protein levels in the three genotype groups and an inverse relationship between Gustin gene methylation and the salivary levels of the protein, mostly evident in AA and ST volunteers, i.e., in volunteers who would be carriers of the functional isoform of the protein. These findings could justify the conflicting data in the literature.

A systematic review of the biological mediators of fat taste and smell

Taste and smell play a key role in our ability to perceive foods. Overconsumption of highly palatable energy-dense foods can lead to increased caloric intake and obesity. Thus there is growing interest in the study of the biological mediators of fat taste and associated olfaction as potential targets for pharmacologic and nutritional interventions in the context of obesity and health. The number of studies examining mechanisms underlying fat taste and smell has grown rapidly in the last 5 years. Therefore, the purpose of this systematic review is to summarize emerging evidence examining the biological mechanisms of fat taste and smell. A literature search was conducted of studies published in English between 2014 and 2021 in adult humans and animal models. Database searches were conducted using PubMed, EMBASE, Scopus, and Web of Science for key terms including fat/lipid, taste, and olfaction. Initially, 4,062 articles were identified through database searches, and a total of 84 relevant articles met inclusion and exclusion criteria and are included in this review. Existing literature suggests that there are several proteins integral to fat chemosensation, including cluster of differentiation 36 (CD36) and G protein-coupled receptor 120 (GPR120). This systematic review will discuss these proteins and the signal transduction pathways involved in fat detection. We also review neural circuits, key brain regions, ingestive cues, postingestive signals, and genetic polymorphism that play a role in fat perception and consumption. Finally, we discuss the role of fat taste and smell in the context of eating behavior and obesity.

The Impact of Taste Preference-Related Gene Polymorphisms on Alcohol Consumption Behavior: A Systematic Review

Unhealthy alcohol consumption is recognized as a leading contributory factor to mortality and disability. In addition to other factors, taste sensation also mediates alcohol intake. The orosensation provoked by alcoholic drinks may vary across individuals and may be responsible for differences in preference for alcoholic beverages. Thus, individual genetic variability of taste preference may have an impact on alcohol consumption practices. The present review aimed to explore the associations between different taste preference polymorphisms and alcohol consumption behavior. Based on the PRISMA statement, the three databases PubMed, Web of Science and ProQuest Central were searched to identify articles and the Q-Genie tool was used to assess the quality of the included studies. Among the 17 studies included in this review, 5 and 12 were of good and moderate quality, respectively. Most of the studies analyzed TAS2R38 (taste 2 receptor member 38) rs713598, rs1726866, rs10246939 polymorphisms. Due to the inconclusive findings on these variants and the very limited number of studies on other polymorphisms, additional extensive research is recommended to replicate the existing findings, to generate new knowledge to enhance our understanding of the complexity of alcohol consumption behavior and to aid the development of personalized recommendations on unhealthy alcohol use.

Exploring the association between oral tactile sensitivity measures and phenotypic markers of oral responsiveness

This study investigated the individual variability in oral tactile sensitivity considering touch, by means of Von Frey Hair monofilaments (VFH) and spatial resolution, using the grating orientation test (GOT). The relationships of the two measures with 6-n-propylthiouracil (PROP) responsiveness and fungiform papillae density and size were investigated. One hundred and forty-four subjects (48.6% women, aged 18-30) participated in the study. VFH and GOT thresholds were assessed by three-down/one-up staircase method. Responsiveness to 3.2mM PROP was assessed on the general Labelled Magnitude Scale. Fungiform papillae density (FPD) and size were determined from automated counting. VFH thresholds appeared unsuitable to reveal individual variation in responsiveness to point-pressure on the tongue. The frequency of GOT thresholds approximated a normal distribution and covered the whole range of variation, thus indicating an ability to measure individual variation in oral tactile sensitivity. No significant linear correlations were found between any of the oral tactile sensitivity measures and PROP responsiveness, FPD total and size class. VFH and GOT thresholds were not significantly associated. Agglomerative hierarchical clustering was used to classify participants for their PROP responsiveness, total FPD and GOT threshold. Three clusters were identified, C1 (n=67), Cl2 (n=42) and Cl3 (n=35), differing for PROP responsiveness and FPD only. Results encourage future studies to explore association between GOT and both perception and preference for different food texture. Furthermore, deeper investigation of individual variability in sensitivity to different types of oral tactile stimuli would be helpful to capture differences in tactile sensitivity among the most sensitive individuals.

Carbonic Anhydrases in Metazoan Model Organisms: Molecules, Mechanisms, and Physiology

During the past three decades, mice, zebrafish, fruit flies, and Caenorhabditis elegans have been the primary model organisms used for the study of various biological phenomena. These models have also been adopted and developed to investigate the physiological roles of carbonic anhydrases (CAs) and carbonic anhydrase-related proteins (CARPs). These proteins belong to eight CA families and are identified by Greek letters: α, β, γ, δ, ζ, η, θ, and ι. Studies using model organisms have focused on two CA families, α-CAs and β-CAs, which are expressed in both prokaryotic and eukaryotic organisms with species-specific distribution patterns and unique functions. This review covers the biological roles of CAs and CARPs in light of investigations performed in model organisms. Functional studies demonstrate that CAs are not only linked to the regulation of pH homeostasis, the classical role of CAs but also contribute to a plethora of previously undescribed functions.

Automated Classification of 6-n-Propylthiouracil Taster Status with Machine Learning

Several studies have used taste sensitivity to 6-n-propylthiouracil (PROP) to evaluate interindividual taste variability and its impact on food preferences, nutrition, and health. We used a supervised learning (SL) approach for the automatic identification of the PROP taster categories (super taster (ST); medium taster (MT); and non-taster (NT)) of 84 subjects (aged 18-40 years). Biological features determined from subjects were included for the training system. Results showed that SL enables the automatic identification of objective PROP taster status, with high precision (97%). The biological features were classified in order of importance in facilitating learning and as prediction factors. The ratings of perceived taste intensity for PROP paper disks (50 mM) and PROP solution (3.2 mM), along with fungiform papilla density, were the most important features, and high estimated values pushed toward ST prediction, while low values leaned toward NT prediction. Furthermore, TAS2R38 genotypes were significant features (AVI/AVI, PAV/PAV, and PAV/AVI to classify NTs, STs, and MTs, respectively). These results, in showing that the SL approach enables an automatic, immediate, scalable, and high-precision classification of PROP taster status, suggest that it may represent an objective and reliable tool in taste physiology studies, with applications ranging from basic science and medicine to food sciences.

Worldwide diversity, association potential, and natural selection in the superimposed taste genes, CD36 and GNAT3

CD36 and GNAT3 mediate taste responses, with CD36 acting as a lipid detector and GNAT3 acting as the α subunit of gustducin, a G protein governing sweet, savory, and bitter transduction. Strikingly, the genes encoding CD36 and GNAT3 are genomically superimposed, with CD36 completely encompassing GNAT3. To characterize genetic variation across the CD36-GNAT3 region, its implications for phenotypic diversity, and its recent evolution, we analyzed from ~2,500 worldwide subjects sequenced by the 1000 Genomes Project (1000GP). CD36-GNAT3 harbored extensive diversity including 8,688 single-nucleotide polymorphisms (SNPs), 414 indels, and other complex variants. Sliding window analyses revealed that nucleotide diversity and population differentiation across CD36-GNAT3 were consistent with genome-wide trends in the 1000GP (π = 0.10%, P = 0.64; FST = 9.0%, P = 0.57). In addition, functional predictions using SIFT and PolyPhen-2 identified 60 variants likely to alter protein function, and they were in weak linkage disequilibrium (r2 < 0.17), suggesting their effects are largely independent. However, the frequencies of predicted functional variants were low (P¯ = 0.0013), indicating their contributions to phenotypic variance on population scales are limited. Tests using Tajima's D statistic revealed that pressures from natural selection have been relaxed across most of CD36-GNAT3 during its recent history (0.39 < P < 0.67). However, CD36 exons showed signs of local adaptation consistent with prior reports (P < 0.035). Thus, CD36 and GNAT3 harbor numerous variants predicted to affect taste sensitivity, but most are rare and phenotypic variance on a population level is likely mediated by a small number of sites.

Association study of taste preference: Analysis in the Lithuanian population

Taste has strong evolutionary basis in the sense of survival by influencing our behavior to obtain food/medicine or avoid poisoning. It is a complex trait and varies among individuals and distinct populations. We aimed to investigate the association between known genetic factors (673 SNPs) and taste preference in the Lithuanian population, as well as to determine a reasonable method for qualitative evaluation of a specific taste phenotype for further genetic analysis. Study group included individuals representing six ethnolinguistic regions of Lithuania. Case and control groups for each taste were determined according to the answers selected to the taste-specific and frequency of specific food consumption questions. Sample sizes (case/control) for each taste are as follows: sweetness (55/179), bitterness (82/208), sourness (32/259), saltiness (42/249), and umami (96/190). Genotypes were extracted from the Illumina HumanOmniExpress-12v1.1 arrays' genotyping data. Analysis was performed using PLINK v1.9. We found associations between the main known genetic factors and four taste preferences in the Lithuanian population: sweetness-genes TAS1R3, TAS1R2, and GNAT3 (three SNPs); bitterness-genes CA6 and TAS2R38 (six SNPs); sourness-genes PKD2L1, ACCN2, PKD1L3, and ACCN1 (48 SNPs); and saltiness-genes SCNN1B and TRPV1 (five SNPs). We found our questionnaire as a beneficial aid for qualitative evaluation of taste preference. This was the first initiative to analyze genetic factors related to taste preference in the Lithuanian population. Besides, this study reproduces, supports, and complements results of previous limited taste genetic studies or ones that lack comprehensive results concerning distinct (ethnic) human populations.

Predominant Qualities Evoked by Quinine, Sucrose, and Capsaicin Associate With PROP Bitterness, but not TAS2R38 Genotype

Genetic variability in the ability to taste thiourea compounds has been studied for 80+ years. Over the last 3 decades, many studies have reported perceived intensity of concentrated propylthiouracil (PROP) associates with greater intensity from a broad range of stimuli, including nonbitter tastants, irritants, and retronasally delivered odorants. Thus, PROP phenotype has become a common measure of individual differences in orosensation. Much, but not all, of the phenotypic variation in PROP bitterness is explained by TAS2R38 polymorphisms. While differences in PROP bitterness are clearly due to genetic variation, mechanistically it is challenging to envision how this receptor (narrowly tuned to the N-C=S moiety) relates to overall orosensory response. Here, we report data for 200+ individuals who had been genotyped for TAS2R38 and phenotyped for PROP in a laboratory setting. Participants also reported the intensity of quinine, capsaicin, and sucrose on a general Labeled Magnitude Scale. Our data recapitulate earlier reports associating PROP bitterness with the intensity of the predominant qualities of sucrose, quinine, and capsaicin; however, we also find correlations between the intensities of sucrose, quinine, and capsaicin were much stronger with each other than with PROP. As expected, TAS2R38 diplotype did not associate with the intensity of sucrose, quinine, or capsaicin. The strength of PROP-capsaicin and PROP-sucrose relationships increased after grouping participants by TAS2R38 diplotype, with the greatest increases in association observed within homozygotes. Collectively, this suggests the suprathreshold intensity of PROP is a confounded phenotype that captures both genetic variation specific to N-C=S compounds and overall orosensation.

Association of single nucleotide polymorphisms with taste and food preferences of the Hungarian general and Roma populations

It is reasonable to suppose that poor diet underlies the unfavorable health status of the Roma population of Europe. Previously in the framework of a complex health survey, fruit and vegetable consumption, quantity of sugar added, salting frequency; bitter, salty, sweet and fat taste preferences were evaluated of Hungarian (HG, n = 410) and Roma (HR, n = 387) populations. In the present study the associations of taste and food preferences with TAS1R3, CD36, SCNN1B, TRPV1, TAS2R38, TAS2R19 and CA6 polymorphisms were tested in the same samples. Genotype frequencies did not differ significantly between the two populations. Although we initially observed associations between certain genetic polymorphisms and taste and food preferences in our study samples, none of the p values remained significant after the multiple test correction. However, some of our results could be considered promising (0.05<corrected p < 0.20), which showed potential ethnicity-specific effects (CA6 rs2274333 with salty taste and raw kohlrabi preference, CD36 rs1527483 with fat taste preference, TAS2R19 rs10772420 with grapefruit preference, and TAS2R38 rs713598 with quantity of sugar added). Our results may suggest that genetics may mediate food preferences, and individuals with different ethnic background may require personalized interventions to modify diet. Further investigations with greater sample sizes are essential to explore the effect of these genetic variants on taste and food preferences.

Addition of chocolate milk to diet corresponds to protein concentration changes in human saliva

Salivary proteins have the potential to alter oral sensory perception of foods. In rodents, dietary polyphenol exposure increases salivary concentrations of polyphenol-binding proteins and several cystatins, which correlate with less aversion to polyphenol-rich solutions. If similar salivary shifts occur in humans, then increasing dietary polyphenols may improve orosensory experience of polyphenol-rich foods. We hypothesized that small dietary changes, focused on polyphenols, would increase expression of salivary binding proteins for polyphenols and thus suppress unpleasant polyphenol sensations. However, analogs of salivary polyphenol-binding proteins are found in foods. Thus, we also hypothesized that food-sourced analogs of these salivary proteins would mitigate changes in saliva and sensation. Human subjects (N=55) alternated weeks of consuming a low polyphenol diet and then a regular diet plus a polyphenol-rich chocolate milk (almond, containing no polyphenol-binding proteins, or bovine, containing polyphenol-binding proteins). Statistical analyses revealed both chocolate milk interventions corresponded to changes in relative expression of 96 proteins and calculated concentration of 146 proteins (both after correction for false discovery rate), out of 1,176 proteins identified through proteomics. Of the proteins that changed, proline-rich proteins and cystatins were noticeable, which reflects prior work in animal studies. Subjects rated all chocolate milks as less flavorful after the bovine chocolate milk intervention week compared to low polyphenol weeks, but generally sensory changes were minimal. However, the results confirm that dietary changes coincide with salivary changes, and that some of those changes occur in proteins that have potential to influence oral sensations.

Time Course of Salivary Protein Responses to Cranberry-Derived Polyphenol Exposure as a Function of PROP Taster Status

Astringency is a complex oral sensation, commonly experienced when dietary polyphenols interact with salivary proteins. Most astringent stimuli alter protein levels, which then require time to be replenished. Although it is standard practice in astringency research to provide breaks in between stimuli, there is limited consensus over the amount of time needed to restore the oral environment to baseline levels. Here we examined salivary protein levels after exposure to 20 mL of a model stimulus (cranberry polyphenol extract, 0.75 g/L CPE) or unsweetened cranberry juice (CJ), over a 10 min period. Whole saliva from healthy subjects (n = 60) was collected at baseline and after 5 and 10 min following either stimulus. Five families of proteins: basic proline-rich proteins (bPRPs); acidic proline-rich proteins (aPRPs); histatins; statherin; and S-type cystatins, were analyzed in whole saliva via HPLC-low resolution-ESI-IT-MS, using the area of the extracted ion current (XIC) peaks. Amylase was quantified via immunoblotting. In comparison to baseline (resting), both stimuli led to a rise in levels of aPRPs (p < 0.000) at 5 min which remained elevated at 10 min after stimulation. Additionally, an interaction of PROP taster status and time was observed, wherein super-tasters had higher levels of amylase in comparison to non-tasters after stimulation with CJ at both timepoints (p = 0.014–0.000). Further, male super-tasters had higher levels of bPRPs at 5 min after stimulation with both CJ and CPE (p = 0.015–0.007) in comparison to baseline. These data provide novel findings of interindividual differences in the salivary proteome that may influence the development of astringency and that help inform the design of sensory experiments of astringency.

Factors affecting flavor perception in space: Does the spacecraft environment influence food intake by astronauts?

The intention to send a crewed mission to Mars involves a huge amount of planning to ensure a safe and successful mission. Providing adequate amounts of food for the crew is a major task, but 20 years of feeding astronauts on the International Space Station (ISS) have resulted in a good knowledge base. A crucial observation from the ISS is that astronauts typically consume only 80% of their daily calorie requirements when in space. This is despite daily exercise regimes that keep energy usage at very similar levels to those found on Earth. This calorie deficit seems to have little effect on astronauts who spend up to 12 months on the ISS, but given that a mission to Mars would take 30 to 36 months to complete, there is concern that a calorie deficit over this period may lead to adverse effects in crew members. The key question is why astronauts undereat when they have a supply of food designed to fully deliver their nutritional needs. This review focuses on evidence from astronauts that foods taste different in space, compared to on Earth. The underlying hypothesis is that conditions in space may change the perceived flavor of the food, and this flavor change may, in turn, lead to underconsumption by astronauts. The key areas investigated in this review for their potential impact on food intake are the effects of food shelf life, physiological changes, noise, air and water quality on the perception of food flavor, as well as the link between food flavor and food intake.

Almli V. Investigating the Relationships between Basic Tastes Sensitivities, Fattiness Sensitivity, and Food Liking in 11-Year-Old Children

This study investigates the relationships between basic tastes and fattiness sensitivity and food liking in 11-year-old children. The basic taste sensitivity of 106 children was measured using different methods, namely detection (DT) and recognition (RT) thresholds, and taste responsiveness. Caffeine and quinine (bitter), sucrose (sweet), citric acid (sour), sodium chloride (salty), and monosodium glutamate (umami) were investigated for DT and RT at five concentrations in water solutions. In addition, taste responsiveness and liking were collected for the high-intensity concentrations. PROP (6-n-propylthiouracil) responsiveness was tested on paper strips. Fattiness sensitivity was measured by a paired comparison method using milk samples with varying fat content. Liking for 30 food items was recorded using a food-list questionnaire. The test was completed in a gamified “taste detective” approach. The results show that DT correlates with RT for all tastes while responsiveness to PROP correlates with overall taste responsiveness. Caffeine and quinine differ in bitterness responsiveness and liking. Girls have significantly lower DTs than boys for bitterness and sweetness. Food liking is driven by taste and fattiness properties, while fatty food liking is significantly influenced by fattiness sensitivity. These results contribute to a better holistic understanding of taste and fattiness sensitivity in connection to food liking in preadolescents.

Salivary proteome of a Neotropical primate: potential roles in host defense and oral food perception

BACKGROUND

Saliva contains a very complex mixture of proteins for defense against microbiological pathogens and for oral food perception. Howler monkeys are Neotropical primates that can consume a mostly leaf diet. They are well known to thrive in highly disturbed habitats where they may cope with a diversity of dietary challenges and infection risks. We aimed to describe the salivary proteome of howlers to contribute to better understanding of their physiology.

METHODS

We analyzed the salivary proteins of wild black howler monkeys (Alouatta pigra), by SDS-PAGE-1-D and Nano LC-MS/MS and categorized them by their function involved in host defense and oral food perception.

RESULTS

Our proteomic analysis identified 156 proteins in howler saliva including a number of host defense peptides that are the first line of defense in mammals, such as defensin, cathelicidin, dermcidin, and lactotransferrin, and proteins with anti-bacterial, anti-fungal, and anti-viral capacity, such as IgA, IgG, IgM, BPI, salivary heat shock 70 kDa protein, beta-2-microbulin, and protein S-100. We also identified key proteins necessary for taste perception, including salivary carbonic anhydrase VI, cystatin D, IgA, and fatty acid-binding protein. Proteins to detect astringent foods were identifying, including four members of cystatins (A, B, C and D), lactoperoxidase, and histidine-rich proteins. No chitinase and amylase were identified as would be expected because howlers do not eat insects and little starch. These findings provide basic information to future studies in oral biology, ingestive physiology, and physiological ecology of mammals and non-human primates.

Taste Changes in Patients with Inflammatory Bowel Disease: Associations with PROP Phenotypes and polymorphisms in the salivary protein, Gustin and CD36 Receptor Genes

Inflammatory bowel disease (IBD) is a chronic inflammatory condition of the gastrointestinal tract resulting from interactions among various factors with diet being one of the most significant. IBD-related dietary behaviors are not clearly related to taste dysfunctions. We analyzed body mass index (BMI) and perception of six taste qualities and assessed effects of specific taste genes in IBD patients and healthy subjects (HC). BMI in IBD patients was higher than in HC subjects. Taste sensitivity to taste qualities was reduced in IBD patients, except for sour taste, which was higher than in HC subjects. Genetic variations were related to some taste responses in HC subjects, but not in IBD patients. Frequencies of genotype AA and allele A in CD36 polymorphism (rs1761667) were significantly higher in IBD patients than in HC subjects. The taste changes observed could be explained by the oral pathologies and microbiome variations known for IBD patients and can justify their typical dietary behaviors. The lack of genetic effects on taste in IBD patients indicates that IBD might compromise taste so severely that gene effects cannot be observed. However, the high frequency of the non-tasting form of CD36 substantiates the fact that IBD-associated fat taste impairment may represent a risk factor for IBD.

Genetic Background of Taste Perception, Taste Preferences, and Its Nutritional Implications: A Systematic Review

Background: The rise in nutrition-related morbidity and mortality requires public health intervention programs targeting nutritional behavior. In addition to socio-economical, socio-cultural, psychological determinants, taste is one of the main factors that influence food choices. Differences in taste perception and sensitivity may be explained by genetic variations, therefore the knowledge of the extent to which genetic factors influence the development of individual taste preferences and eating patterns is important for public policy actions addressing nutritional behaviors. Our aim was to review genetic polymorphisms accounting for variability in taste and food preferences to contribute to an improved understanding of development of taste and food preferences.

Methods: The electronic databases PubMed, Scopus, and Web of Science were searched using MeSH in PubMed and free text terms for articles published between January 1, 2000 and April 13, 2018. The search strategy was conducted following the PRISMA statement. The quality of the included studies was assessed by the validated Q-Genie tool.

Results: Following the PRISMA flowchart, finally 103 articles were included in the review. Among the reviewed studies, 43 were rated to have good quality, 47 were rated to have moderate quality, and 13 were rated to have low quality. The majority of the studies assessed the association of genetic variants with the bitter taste modality, followed by articles analyzing the impact of polymorphisms on sweet and fat preferences. The number of studies investigating the association between umami, salty, and sour taste qualities and genetic polymorphisms was limited.

Conclusions: Our findings suggest that a significant association exists between TAS2R38 variants (rs713598, rs1726866, rs10246939) and bitter and sweet taste preference. Other confirmed results are related to rs1761667 (CD36) and fat taste responsiveness. Otherwise further research is essential to confirm results of studies related to genetic variants and individual taste sensitivity. This knowledge may enhance our understanding of the development of individual taste and related food preferences and food choices that will aid the development of tailored public health strategy to reduce nutrition-related disease and morbidity.

New insights into the relationship between taste perception and oral microbiota composition

Fairly poor data are available on the relationship between taste perception, food preferences and oral microbiota. In the present study, we investigated the hypothesis that subjects with higher responsiveness to 6-n-propylthiuracil (PROP) might be characterized by a different taste sensitivity and tongue microbiota composition. Indeed, the bacterial metabolism may modulate/enhance the concentration of tastants near the taste receptors, modifying taste perception through a sensorial adaptation mechanism or by a broad range of microbial metabolic pathways. The detection thresholds of sweet, sour, salty and bitter, the Fungiform Papillae Density (FPD) and the composition of bacteria lining the tongue were determined in Supertasters (high PROP responsiveness, ST) and Non-tasters (low PROP responsiveness, NT). An important inter-individual variability was found for all taste stimuli and FPD between the two groups, with NT subjects showing significant higher threshold values and a lower FPD than with STs. We found five bacterial genera whose relative abundances were significantly higher in STs than NTs. This study opens new avenues of research by highlighting associations between parameters usually studied independently.

Carbonic Anhydrase 6 Gene Variation influences Oral Microbiota Composition and Caries Risk in Swedish adolescents

Carbonic anhydrase VI (CA6) catalyses the reversible hydration of carbon dioxide in saliva with possible pH regulation, taste perception, and tooth formation effects. This study assessed effects of variation in the CA6 gene on oral microbiota and specifically the acidophilic and caries-associated Streptococcus mutans in 17-year old Swedish adolescents (n = 154). Associations with caries status and secreted CA6 protein were also evaluated. Single Nucleotide Polymorphisms (27 SNPs in 5 haploblocks) and saliva and tooth biofilm microbiota from Illumina MiSeq 16S rDNA (V3-V4) sequencing and culturing were analysed. Haploblock 4 (rs10864376, rs3737665, rs12138897) CCC associated with low prevalence of S. mutans (OR (95% CI): 0.5 (0.3, 0.8)), and caries (OR 0.6 (0.3, 0.9)), whereas haploblock 4 TTG associated with high prevalence of S. mutans (OR: 2.7 (1.2, 5.9)) and caries (OR: 2.3 (1.2, 4.4)). The TTG-haploblock 4 (represented by rs12138897(G)) was characterized by S. mutans, Scardovia wiggsiae, Treponema sp. HOT268, Tannerella sp. HOT286, Veillonella gp.1 compared with the CCC-haploblock 4 (represented by rs12138897(C)). Secreted CA6 in saliva was weakly linked to CA6 gene variation. In conclusion, the results indicate that CA6 gene polymorphisms influence S. mutans colonization, tooth biofilm microbiota composition and risk of dental caries in Swedish adolescents.

Comparison of salivary proteome of children with different sensitivities for bitter and sweet tastes: association with body mass index

BACKGROUND/OBJECTIVES

Oral sensorial perception is a key aspect in food choices and knowing the mechanisms modulating such perception is of major importance in the context of child obesity, which is reaching high rates in Mediterranean countries. Salivary proteome has been linked to taste sensitivity in adults. The aim of this study was to search for differences in salivary proteomes of children with different bitter or sweet taste sensitivities and to assess if these potential differences are associated with their body mass index percentile (BMI percentile).

SUBJECTS/METHODS

387 children aged 8-9 years old were assessed for BMI percentile and classified according to their sensitivity to bitter and sweet tastes, according to their caffeine and sucrose detection thresholds, respectively. Saliva protein composition was compared among taste sensitivity groups, taking into account BMI percentile and gender, using gel-based proteomics approaches, coupled to mass spectrometry for protein identification.

RESULTS

Among the salivary proteins related to bitter taste sensitivity, higher levels of cystatins were observed in bitter-sensitive children, in the case of those of normal weight, and in bitter low-sensitive, in the case of overweight children. For sweetness, the relationship between saliva and taste perception was also dependent on BMI percentile, with several proteins (including salivary cystatins) differing between taste sensitivity groups, with disparities arising between normal-weight and overweight children. Cystatin isoforms A, B and SA were observed to be considerably increased in saliva from obese children.

CONCLUSIONS

Salivary proteome is related with sensitivities to bitter and sweet tastes in children, but the association is dependent on BMI percentile and gender.

Carbonic Anhydrases: Role in pH Control and Cancer

The pH of the tumor microenvironment drives the metastatic phenotype and chemotherapeutic resistance of tumors. Understanding the mechanisms underlying this pH-dependent phenomenon will lead to improved drug delivery and allow the identification of new therapeutic targets. This includes an understanding of the role pH plays in primary tumor cells, and the regulatory factors that permit cancer cells to thrive. Over the last decade, carbonic anhydrases (CAs) have been shown to be important mediators of tumor cell pH by modulating the bicarbonate and proton concentrations for cell survival and proliferation. This has prompted an effort to inhibit specific CA isoforms, as an anti-cancer therapeutic strategy. Of the 12 active CA isoforms, two, CA IX and XII, have been considered anti-cancer targets. However, other CA isoforms also show similar activity and tissue distribution in cancers and have not been considered as therapeutic targets for cancer treatment. In this review, we consider all the CA isoforms and their possible role in tumors and their potential as targets for cancer therapy.

Factors Influencing the Phenotypic Characterization of the Oral Marker, PROP

In the last several decades, the genetic ability to taste the bitter compound, 6-n-propyltiouracil (PROP) has attracted considerable attention as a model for understanding individual differences in taste perception, and as an oral marker for food preferences and eating behavior that ultimately impacts nutritional status and health. However, some studies do not support this role. This review describes common factors that can influence the characterization of this phenotype including: (1) changes in taste sensitivity with increasing age; (2) gender differences in taste perception; and (3) effects of smoking and obesity. We suggest that attention to these factors during PROP screening could strengthen the associations between this phenotype and a variety of health outcomes ranging from variation in body composition to oral health and cancer risk.

Salivary proteome and glucose levels are related with sweet taste sensitivity in young adults

Sweet taste plays a critical role in determining food preferences and choices. Similar to what happens for other oral sensations, individuals differ in their sensitivity for sweet taste and these inter-individual differences may be responsible for variations in food acceptance. Despite evidence that saliva plays a role in taste perception, this fluid has been mainly studied in the context of bitterness or astringency. We investigated the possible relationship between sweet taste sensitivity and salivary composition in subjects with different sucrose detection thresholds. Saliva collected from 159 young adults was evaluated for pH, total protein concentration and glucose. One- and bi-dimensional electrophoresis (2-DE) were performed and protein profiles compared between sweet sensitivity groups, with proteins that were differently expressed being identified by MALDI-FTICR-MS. Moreover, Western blotting was performed for salivary carbonic anhydrase VI (CA-VI) and cystatins and salivary amylase enzymatic activity was assessed in order to compare groups. Females with low sensitivity to sweet taste had higher salivary concentrations of glucose compared to those with sensitivity. For protein profiles, some differences were sex-dependent, with higher levels of α-amylase and CA-VI in low-sensitivity individuals and higher levels of cystatins in sensitive ones for both sexes. Body mass index was not observed to affect the association between salivary proteome and taste sensitivity. To our knowledge, these are the first data showing an association between sweet taste and saliva proteome.

Association of tongue brushing with the number of fungiform taste buds and taste perception: A preliminary study using confocal laser scanning microscopy in combination with a filter-paper disc method

OBJECTIVE

The aim of this study was to investigate the association of tongue brushing with the number of fungiform taste buds and taste perception using a confocal laser scanning microscopy in combination with a filter-paper disc method (FPDM).

METHODS

Twenty-four subjects with or without a habit of tongue brushing (11 males and 13 females, 20-46 years old) participated in this study. Nine of the 24 subjects had no habit of tongue brushing (Group 1, n=9). Fifteen subjects had a habit of tongue brushing, and the brushing regions of the tongue were as follows: central region (Group 2, n=7), or entire region (Group 3, n=8) of the tongue dorsum. Using confocal laser scanning microscopy, the average number of taste buds per fungiform papilla (FP) was counted. Taste perception was evaluated using an FPDM. These observations were performed in the midlateral region of the tongue since the distribution of fungiform papillae is large in the midlateral region compared to that in the central region.

RESULTS

The subjects in Group 3 showed a significantly decreased number of fungiform taste buds compared to Group 1 and Group 2. Group 3 also showed significantly higher FPDM scores than the other two groups.

CONCLUSIONS

Excessive tongue brushing of the entire tongue dorsum, including the midlateral region, may have an association with the decreased number of FP and taste buds and decreased taste sensation. To avoid these conditions, instituting proper tongue brushing methods, such as limiting it to the central region of the tongue and using a light touch, is suggested and is important for the subjects who are eager to participate in tongue brushing.

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.

Past exposure to fruit and vegetable variety moderates the link between fungiform papillae density and current variety of FV consumed by children

Higher fungiform papillae density (FPD) has been associated with lower taste sensitivity thresholds and greater perceived taste intensity along with consumption of fewer fruit and vegetables (FV). Children exposed to greater variety of FV tend to habitually consume more FV, however, it is unknown whether exposure effects are attenuated by individual differences in FPD or whether these effects vary according to sensory properties of FV. This study examined the links between children's FPD, current variety of FV consumed, and past experiences with variety of fruit and vegetables. FPD counts were obtained from 61 children between 5 and 9years old, in schools from affluent areas of Birmingham (UK). Parents completed food frequency questionnaires indicating the variety of FV consumed by children in the last 7days. Parents also indicated the number of different FV types the children had tasted in their lifetime. FV were subdivided to reflect differences in their sensory properties. The results showed that children with higher FPD who in their lifetime had tasted a greater variety of FV ate a larger variety of FV compared to children with higher FPD, but with lower past exposure. When examining effects within specific subcategories of fruits and vegetables, this pattern held for non-astringent fruit and showed a trend for non-bitter vegetables. Children with lower FPD consumed similar variety of FV irrespective of past experiences with variety of FV. The results suggest that when strong or irritant sensory food properties are not a barrier to intake, higher FPD in the presence of supportive home food environment may be beneficial for FV intake. Individual phenotypic differences may affect responsiveness to environmental factors in children's intake of FV.

Sensory perception of and salivary protein response to astringency as a function of the 6-n-propylthioural (PROP) bitter-taste phenotype

Individual differences in astringency perception are poorly understood. Astringency from tannins stimulates the release of specific classes of salivary proteins. These proteins form complexes with tannins, altering their perceived astringency and reducing their bioavailability. We studied the bitter compound, 6-n-propylthioural (PROP), as a phenotypic marker for variation in astringency perception and salivary protein responses. Seventy-nine subjects classified by PROP taster status rated cranberry juice cocktail (CJC; with added sugar) supplemented with 0, 1.5 or 2.0g/L tannic acid (TA). Saliva for protein analyses was collected at rest, or after stimulation with TA or cranberry juice (CJ; without added sugar). CJC with 1.5g/L tannic acid was found to be less astringent, and was liked more by PROP non-taster males than PROP taster males, consistent with the expectation that non-tasters are less sensitive to astringency. Levels of acidic Proline Rich Proteins (aPRPs) and basic Proline Rich Proteins (bPRPs) decreased after TA, while levels of aPRPs, bPRPs and Cystatins unexpectedly rose after CJ. Increases in bPRPs and Cystatins were only observed in PROP tasters. The PROP phenotype plays a gender-specific, but somewhat limited role in the perceived astringency of tannic-acid supplemented, cranberry juice cocktail. The PROP phenotype (regardless of gender) may also be involved in the release of salivary proteins previously implicated in oral health.

Caries risk in children of Udaipur City, India using genetic taste sensitivity to 6-n-propylthiouracil

Aims and Objectives:

Dental caries still remains the single most common disease of childhood. The present study was conducted to test the hypothesis that a higher prevalence of dental caries would be observed among nontaster children compared to medium tasters or supertasters of 6n propylthiouracil impregnated filter papers.

Materials and Methods:

The present study was conducted on a random sample of 600 school children aged 6–12 years in Udaipur city. 6-n-propylthiouracil strips were prepared. The food preference questionnaire was filled by the participants, and their decayed missing filled status as well as taste sensitivity to the propylthiouracil impregnated filter papers were noted. The data obtained was then used for statistical analysis using chi square, analysis of variance, and Students t-tests with the consult of a statistician using the Statistical Package for the Social Sciences version 17 software.

Results:

Nontasters had a greater caries experience than the supertasters and medium tasters. Females were found to be more tasters than nontasters. It was also found that nontasters belonged to caries active group more than the tasters.

Conclusion:

The caries status was higher among the nontaster children with more sweet preference than in taster children and they belonged more to the caries active group.

Oral sensory nerve damage: Causes and consequences

Oral sensations (i.e., taste, oral somatosensation, retronasal olfaction) are integrated into a composite sense of flavor, which guides dietary choices with long-term health impact. The nerves carrying this input are vulnerable to peripheral damage from multiple sources (e.g., otitis media, tonsillectomy, head injury), and this regional damage can boost sensations elsewhere in the mouth because of central interactions among nerve targets. Mutual inhibition governs this compensatory process, but individual differences lead to variation in whole-mouth outcomes: some individuals are unaffected, others experience severe loss, and some encounter sensory increases that may (if experienced early in life) elevate sweet-fat palatability and body mass. Phantom taste, touch, or pain sensations (e.g., burning mouth syndrome) may also occur, particularly in those expressing the most taste buds. To identify and treat these conditions effectively, emerging clinical tests measure regional vs. whole-mouth sensation, stimulated vs. phantom cues, and oral anatomy. Scaling methods allowing valid group comparisons have strongly aided these efforts. Overall, advances in measuring oral sensory function in health and disease show promise for understanding the varied clinical consequences of nerve damage.

Variation in the Ability to Taste Bitter Thiourea Compounds: Implications for Food Acceptance, Dietary Intake, and Obesity Risk in Children

The ability to taste bitter thiourea compounds, such as phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP), is inherited. Polymorphisms in the bitter-taste receptor TAS2R38 explain the majority of phenotypic variation in the PROP phenotype. It has been hypothesized that the PROP phenotype is a marker for perception of a variety of chemosensory experiences. In this review, we discuss studies that have investigated the relationship between bitter-taste response and dietary behaviors and chronic health in children. Investigators have hypothesized that children who are PROP tasters have lower liking and consumption of bitter foods, such as cruciferous vegetables. Additionally, several studies suggest that children who are unable to taste PROP (i.e., nontasters) like and consume more dietary fat and are prone to obesity. The relationship between the PROP phenotype and obesity is influenced by multiple confounders, including sex, food access, ethnicity, and socioeconomic status. Future studies that adjust for these variables are needed.

Differential bitterness in capsaicin, piperine, and ethanol associates with polymorphisms in multiple bitter taste receptor genes

To date, the majority of research exploring associations with genetic variability in bitter taste receptors has understandably focused on compounds and foods that are predominantly or solely perceived as bitter. However, other chemosensory stimuli are also known to elicit bitterness as a secondary sensation. Here we investigated whether TAS2R variation explains individual differences in bitterness elicited by chemesthetic stimuli, including capsaicin, piperine and ethanol. We confirmed that capsaicin, piperine and ethanol elicit bitterness in addition to burning/stinging sensations. Variability in perceived bitterness of capsaicin and ethanol were significantly associated with TAS2R38 and TAS2R3/4/5 diplotypes. For TAS2R38, PAV homozygotes perceived greater bitterness from capsaicin and ethanol presented on circumvallate papillae, compared to heterozygotes and AVI homozygotes. For TAS2R3/4/5, CCCAGT homozygotes rated the greatest bitterness, compared to heterozygotes and TTGGAG homozygotes, for both ethanol and capsaicin when presented on circumvallate papillae. Additional work is needed to determine how these and other chemesthetic stimuli differ in bitterness perception across concentrations and presentation methods. Furthermore, it would be beneficial to determine which TAS2R receptors are activated in vitro by chemesthetic compounds.

TongueSim: Development of an Automated Method for Rapid Assessment of Fungiform Papillae Density for Taste Research

Taste buds are found on the tongue in 3 types of structures: the fungiform papillae, the foliate papillae, and the circumvallate papillae. Of these, the fungiform papillae (FP) are present in the greatest numbers on the tongue, and are thought to be correlated to the overall number of taste buds. For this reason, FP density on the tongue is often used to infer taste function, although this has been controversial. Historically, videomicroscopy techniques were used to assess FP. More recently, advances in digital still photography and in software have allowed the development of rapid methods for obtaining high quality images in situ. However, these can be subject to inter-researcher variation in FP identification, and are somewhat limited in the parameters that can be measured. Here, we describe the development of a novel, automated method to count the FP, using the TongueSim suite of software. Advantages include the reduction in time required for image analysis, elimination of researcher bias, and the added potential to measure characteristics such as the degree of roundness of each papilla. We envisage that such software has a wide variety of novel research applications.

Development of a molecular method for the rapid screening and identification of the three functionally relevant polymorphisms in the human TAS2R38 receptor gene in studies of sensitivity to the bitter taste of PROP

The objective of this work was to develop a rapid screening method to identify the three single nucleotide polymorphisms (SNPs) in the TAS2R38 gene, with the aim of providing a significant contribution to studies designed to assess sensitivity to the bitter taste of 6-n-propylthiouracil (PROP). Specifically, the objective of this study was to characterize the TAS2R38 gene haplotypes in a group of 60 subjects with variable sensitivity to PROP and preliminarily genotyped for the rs2274333 allele (A/G) of carbonic anhydrase isoform VI gene (CA6). The molecular characterization of the TAS2R38 gene was conducted using the PCR-restriction fragment length polymorphism technique after creating artificial restriction sites upstream or downstream of the SNPs, as none of the three polymorphisms contributes to the formation of a restriction site for a specific endonuclease. The results indicate that the method described in this paper could be a valid and simple experimental strategy to identify genetic differences related to taste sensitivity to bitter taste, and could be applied as a nutrigenetics test in studies aimed at understanding people’s eating behaviors.

Changes in the salivary protein profile of morbidly obese women either previously subjected to bariatric surgery or not

Saliva is a non-invasive source of biomarkers useful in the study of physiological mechanisms. Moreover, this fluid has diverse functions, among which food perception and ingestion, making it particularly suitable for the study of obesity. The aims of this study were to assess changes in salivary proteome among morbidly obese women, with a view to provide information about mechanisms potentially related to the development of obesity, and to evaluate whether these changes persist after weight loss. Mixed saliva samples from morbidly obese women (N = 18) who had been either subjected (group O-BS) or not (group O) to bariatric surgery and women with normal weight (N = 14; group C) were compared for protein profiles, alpha-amylase abundance and enzymatic activity, and carbonic anhydrase (CA) VI abundance. Differences in salivary obese profiles were observed for 23 different spots. Zinc-alpha-2 glycoprotein-containing spots showed higher abundance in group O only, whereas cystatin S-containing spots presented higher abundance in the two groups of obese subjects. Most of the spots identified as salivary amylase were present at lower levels in group O-BS. With regard to the amylase enzymatic activity, increases were observed for group O and decreases for group O-BS. One interesting finding was the high correlation between levels of CA VI and body mass index in group O, which was not observed for groups O-BS or C. The differences between groups, mainly regarding salivary proteins involved in taste sensitivity and metabolism, point to the potential of using saliva in the study of obesity development.

Salivary Composition Is Associated with Liking and Usual Nutrient Intake

Salivary flow and composition have an impact on flavor perception. However, very few studies have explored the relationship between saliva, individual liking and usual dietary intake. The aim of our study was to evaluate the association of salivary flow and composition with both a liking for fat, saltiness and sweetness and the usual nutrient intake in an adult French population. Liking for fat, saltiness, and sweetness were inferred from liking scores obtained during hedonic tests on 32 food products among 282 French adults participating in the Nutrinet-Santé Study. Before assessing liking, resting saliva was collected. Standard biochemical analyses were performed to assess specific component concentrations and enzymatic activities. Dietary data were collected using three web-based 24h records. Relationships between salivary flow and composition, sensory liking and nutrient intake were assessed using linear regression. Total antioxidant capacity was positively associated with simple carbohydrate intake (β = 31.3, 95% CI = 1.58; 60.99) and inversely related to complex carbohydrate consumption (β = -52.4, 95% CI = -87.51; -19.71). Amylolysis was positively associated with both total (β = 0.20, 95% CI = 0.01; 0.38) and simple carbohydrate intake (β = 0.21, 95% CI = 0.01; 0.39). Salivary flow was positively associated with liking for fat (β = 0.14, 95% CI = 0.03; 0.25). Proteolysis was positively associated with liking for saltiness and for fat (β = 0.31, 95% CI = 0.02; 0.59; β = 0.28, 95% CI = 0.01; 0.56, respectively). Amylolysis was inversely associated with liking for sweetness (β = -10.13, 95% CI = -19.51; -0.75). Carbonic anhydrase 6 was inversely associated with liking for saltiness (β = -46.77, 95% CI = -86.24; -7.30). Saliva does not substantially vary according to a usual diet, except for carbohydrate intake, whereas the specific association between salivary flow/composition and sensory liking suggests the influence of saliva characteristics in food acceptance.

Dose-Dependent Effects of L-Arginine on PROP Bitterness Intensity and Latency and Characteristics of the Chemical Interaction between PROP and L-Arginine

Genetic variation in the ability to taste the bitterness of 6-n-propylthiouracil (PROP) is a complex trait that has been used to predict food preferences and eating habits. PROP tasting is primarily controlled by polymorphisms in the TAS2R38 gene. However, a variety of factors are known to modify the phenotype. Principle among them is the salivary protein Ps-1 belonging to the basic proline-rich protein family (bPRP). Recently, we showed that oral supplementation with Ps-1 as well as its related free amino acids (L-Arg and L-Lys) enhances PROP bitterness perception, especially for PROP non-tasters who have low salivary levels of Ps-1. Here, we show that salivary L-Arg levels are higher in PROP super-tasters compared to medium tasters and non-tasters, and that oral supplementation with free L-Arg enhances PROP bitterness intensity as well as reduces bitterness latency in a dose-dependent manner, particularly in individuals with low salivary levels of both free L-Arg and Ps-1 protein. Supplementation with L-Arg also enhanced the bitterness of caffeine. We also used 1H-NMR spectroscopy and quantum-mechanical calculations carried out by Density Functional Theory (DFT) to characterize the chemical interaction between free L-Arg and the PROP molecule. Results showed that the -NH2 terminal group of the L-ArgH+ side chain interacts with the carbonyl or thiocarbonyl groups of PROP by forming two hydrogen bonds with the resulting charged adduct. The formation of this PROP•ArgH+ hydrogen-bonded adduct could enhance bitterness intensity by increasing the solubility of PROP in saliva and its availability to receptor sites. Our data suggest that L-Arg could act as a 'carrier' of various bitter molecules in saliva.