Bitterness of the non-nutritive sweetener acesulfame potassium varies with polymorphisms in TAS2R9 and TAS2R31

Secondary Analysis of Sweetness Liking from Pilot Study Replacing Sugar Sweetened Soda with Flavored, Unsweetened Sparkling Water

OBJECTIVE

This study aimed to evaluate changes in sensory ratings (liking, sweetness intensity, "just about right" (JAR) level of sweetness) of 0-10.7% w/w sugar in soda after 1 and 2 wk of replacing sugar-sweetened soda consumption with unsweetened, flavored, sparkling water.

METHODS

Consumers of sugar-sweetened sodas (17 men and women, average age 28 years) replaced their sodas with unsweetened, flavored sparkling waters for 2 wk. Changes in sensory ratings were evaluated for sodas ranging from 0-10.7% w/w added sugar. In a secondary analysis, cluster analysis identified "Sweet Likers" (liking increased with sugar concentration) and "Sweet Moderates" (liking peaked in the middle of the concentration range) in the baseline ratings, and models for changes in sensory ratings were reevaluated by sweet-liking group.

RESULTS

The primary analyses showed no significant effects of the intervention on sweetness intensity or liking ratings. However, the secondary analysis showed that Sweet Likers reduced liking ratings for all sodas, but particularly for the highest concentration (p = 0.0021) after the intervention. Sweet Moderates, however, increased liking ratings after the intervention, driven by an increase in liking for the lower concentrations of sugar (p = 0.0058). Additionally, Sweet Moderates increased their overall ratings for sweetness intensity in sodas (p = 0.00074).

CONCLUSION

These results suggest that the intervention may have been more successful in shifting sensory perception and acceptance of less-sweet sodas for Sweet Moderates than for Sweet Likers. These results should be verified in a larger sample that intentionally recruits by sweet liker status, to see if initial liking for sweetness may be a critical factor in interventions aiming to improve liking of less sweet beverages.

Differential Activation of TAS2R4 May Recover Ability to Taste Propylthiouracil for Some TAS2R38 AVI Homozygotes

Bitterness from phenylthiocarbamide and 6-n-propylthiouracil (PROP) varies with polymorphisms in the TAS2R38 gene. Three SNPs form two common (AVI, PAV) and four rare haplotypes (AAI, AAV, PVI, and PAI). AVI homozygotes exhibit higher detection thresholds and lower suprathreshold bitterness for PROP compared to PAV homozygotes and heterozygotes, and these differences may influence alcohol and vegetable intake. Within a diplotype, substantial variation in suprathreshold bitterness persists, and some AVI homozygotes report moderate bitterness at high concentrations. A second receptor encoded by a gene containing a functional polymorphism may explain this. Early work has suggested that PROP might activate TAS2R4 in vitro, but later work did not replicate this. Here, we identify three TAS2R4 SNPs that result in three diplotypes-SLN/SLN, FVS/SLN, and FVS/FVS-which make up 25.1%, 44.9%, and 23.9% of our sample. These TAS2R4 haplotypes show minimal linkage disequilibrium with TAS2R38, so we examined the suprathreshold bitterness as a function of both. The participants (n = 243) rated five PROP concentrations in duplicate, interleaved with other stimuli. As expected, the TAS2R38 haplotypes explained ~29% (p < 0.0001) of the variation in the bitterness ratings, with substantial variation within the haplotypes (AVI/AVI, PAV/AVI, and PAV/PAV). Notably, the TAS2R4 diplotypes (independent of the TAS2R38 haplotypes) explained ~7-8% of the variation in the bitterness ratings (p = 0.0001). Given this, we revisited if PROP could activate heterologously expressed TAS2R4 in HEK293T cells, and calcium imaging indicated 3 mM PROP is a weak TAS2R4 agonist. In sum, our data are consistent with the second receptor hypothesis and may explain the recovery of the PROP tasting phenotype in some AVI homozygotes; further, this finding may potentially help explain the conflicting results on the TAS2R38 diplotype and food intake.

Genetic Variation and Sensory Perception of a Pediatric Formulation of Ibuprofen: Can a Medicine Taste Too Good for Some?

There is wide variation in how individuals perceive the chemosensory attributes of liquid formulations of ibuprofen, encompassing both adults and children. To understand personal variation in the taste and chemesthesis properties of this medicine, and how to measure it, our first scientific strategy centered on utilizing trained adult panelists, due to the complex and time-consuming psychophysical tasks needed at this initial stage. We conducted a double-blind cohort study in which panelists underwent whole-genome-wide genotyping and psychophysically evaluated an over-the-counter pediatric medicine containing ibuprofen. Associations between sensory phenotypes and genetic variation near/within irritant and taste receptor genes were determined. Panelists who experienced the urge to cough or throat sensations found the medicine less palatable and sweet, and more irritating. Perceptions varied with genetic ancestry; panelists of African genetic ancestry had fewer chemesthetic sensations, rating the medicine sweeter, less irritating, and more palatable than did those of European genetic ancestry. We discovered a novel association between TRPA1 rs11988795 and tingling sensations, independent of ancestry. We also determined for the first time that just tasting the medicine allowed predictions of perceptions after swallowing, simplifying future psychophysical studies on diverse populations of different age groups needed to understand genetic, cultural-dietary, and epigenetic factors that influence individual perceptions of palatability and, in turn, adherence and the risk of accidental ingestion.

Association between Genetic Variation in the TAS2R38 Bitter Taste Receptor and Propylthiouracil Bitter Taste Thresholds among Adults Living in Japan Using the Modified 2AFC Procedure with the Quest Method

Individual taste sensitivity influences food preferences, nutritional control, and health, and differs greatly between individuals. The purpose of this study was to establish a method of measuring and quantifying an individual's taste sensitivity and to evaluate the relationship between taste variation and genetic polymorphisms in humans using agonist specificities of the bitter taste receptor gene, TAS2R38, with the bitter compound 6-n-propylthiouracil (PROP). We precisely detected the threshold of PROP bitter perception by conducting the modified two-alternative forced-choice (2AFC) procedure with the Bayesian staircase procedure of the QUEST method and examined genetic variation in TAS2R38 in a Japanese population. There were significant differences in PROP threshold between the three TAS2R38 genotype pairs for 79 subjects: PAV/PAV vs AVI/AVI, p < 0.001; PAV/AVI vs AVI/AVI, p < 0.001; and PAV/PAV vs PAV/AVI, p < 0.01. Our results quantified individual bitter perception as QUEST threshold values: the PROP bitter perception of individuals with the PAV/PAV or PAV/AVI genotypes was tens to fifty times more sensitive than that of an individual with the AVI/AVI genotype. Our analyses provide a basic model for the accurate estimation of taste thresholds using the modified 2AFC with the QUEST approach.

Taste Preference-Related Genetic Polymorphisms Modify Alcohol Consumption Behavior of the Hungarian General and Roma Populations

Harmful alcohol consumption has been considered a major public health issue globally, with the amounts of alcohol drunk being highest in the WHO European Region including Hungary. Alcohol consumption behaviors are complex human traits influenced by environmental factors and numerous genes. Beyond alcohol metabolization and neurotransmitter gene polymorphisms, taste preference-related genetic variants may also mediate alcohol consumption behaviors. Applying the Alcohol Use Disorders Identification Test (AUDIT) we aimed to elucidate the underlying genetic determinants of alcohol consumption patterns considering taste preference gene polymorphisms (TAS1R3 rs307355, TAS2R38 rs713598, TAS2R19 rs10772420 and CA6 rs2274333) in the Hungarian general (HG) and Roma (HR) populations. Alcohol consumption assessment was available for 410 HG and 387 HR individuals with 405 HG and 364 HR DNA samples being obtained for genotyping. No significant associations were found between TAS1R3 rs307355, TAS2R19 rs10772420, and CA6 rs2274333 polymorphisms and alcohol consumption phenotypes. Significant associations were identified between TAS2R38 rs713598 and the number of standard drinks consumed in the HG sample (genotype GG negatively correlated with the number of standard drinks; coef: -0.136, p = 0.028) and the prevalence of having six or more drinks among Roma (a negative correlation was identified in the recessive model; genotype GG, coef: -0.170, p = 0.049), although, none of these findings passed the Bonferroni-corrected probability criterion (p > 0.05). Nevertheless, our findings may suggest that alcohol consumption is partially driven by genetically determined taste preferences in our study populations. Further studies are required to strengthen the findings and to understand the drivers of alcohol consumption behavior in more depth.

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.

Variation in TAS2R receptor genes explains differential bitterness of two common antibiotics

For pharmaceuticals to deliver their full benefits with maximum efficacy, patients need to follow recommended dosing schedules, in terms of amount and frequency. Unfortunately, the aversive taste of many drugs, especially bitterness, can reduce patient compliance in oral liquid formulations. Given common genetic differences in bitter taste receptor genes (TAS2Rs), some individuals may be at increased risk for poor compliance due to heightened bitterness that becomes a barrier to proper use. Here we report on the sensory profile of two antibiotics, chloramphenicol and ofloxacin, investigating whether bitterness intensity associates with nominally functional TAS2R variants. Participants (n = 143) rated suprathreshold intensity on a general Labeled Magnitude Scale (gLMS) for chloramphenicol and ofloxacin; propylthiouracil (PROP) was included as a control, given robust prior associations with TAS2R38 variants. The dominant sensation from chloramphenicol and ofloxacin was bitterness, falling just below “moderate” on a gLMS. TAS2R38 diplotype associated with variable bitterness of chloramphenicol and PROP, but not ofloxacin. The bitterness of ofloxacin associated with a TAS2R9 SNP (V187A). This pilot study provides novel evidence on differences in the bitterness from two antibiotics, which are associated with TAS2R variants. Improved understanding of individualized barriers to patient compliance, especially for oral formulations, can guide future efforts to optimize delivery systems for improved compliance.

Flavour Generation during Lactic Acid Fermentation of Brassica Vegetables—Literature Review

Fermentation is a method of food preservation that has been used for centuries. Lactic acid fermentation, apart from extending the shelf-life of vegetables, affects significantly the flavour of food products. In this review, the formation of flavour, including both taste and aroma, in fermented Brassica vegetables is summarized. The flavour-active compounds are generated in various metabolic pathways from many precursors present in raw materials used for fermentation. In Brassica vegetables, a unique group of chemicals, namely glucosinolates, is present, which significantly influence the flavour of fermented products. In this summary, we took a closer look at the flavour of two of the most commonly eaten worldwide fermented Brassica products, which are sauerkraut and kimchi. Finally, the needs and directions for future studies were addressed.

An update on extra-oral bitter taste receptors

Bitter taste-sensing type 2 receptors (TAS2Rs or T2Rs), belonging to the subgroup of family A G-protein coupled receptors (GPCRs), are of crucial importance in the perception of bitterness. Although in the first instance, TAS2Rs were considered to be exclusively distributed in the apical microvilli of taste bud cells, numerous studies have detected these sensory receptor proteins in several extra-oral tissues, such as in pancreatic or ovarian tissues, as well as in their corresponding malignancies. Critical points of extra-oral TAS2Rs biology, such as their structure, roles, signaling transduction pathways, extensive mutational polymorphism, and molecular evolution, have been currently broadly studied. The TAS2R cascade, for instance, has been recently considered to be a pivotal modulator of a number of (patho)physiological processes, including adipogenesis or carcinogenesis. The latest advances in taste receptor biology further raise the possibility of utilizing TAS2Rs as a therapeutic target or as an informative index to predict treatment responses in various disorders. Thus, the focus of this review is to provide an update on the expression and molecular basis of TAS2Rs functions in distinct extra-oral tissues in health and disease. We shall also discuss the therapeutic potential of novel TAS2Rs targets, which are appealing due to their ligand selectivity, expression pattern, or pharmacological profiles.

Variation in type two taste receptor genes is associated with bitter tasting phenylthiocarbamide consumption in mature Targhee and Rambouillet rams

Bitter taste perception in sheep can lead to avoidance of specific types of forage, such as sagebrush, which is present on many rangeland grazing systems in the Intermountain West. In humans, bitter taste perception is influenced by variation in several TAS2R genes, including more extensively studied TAS2R38 and TAS2R16. We hypothesize that variation in taste receptor genes in sheep is associated with bitter taste. Therefore, the objective of this study was to examine variation in TAS2R genes in relation to consumption of a bitter tasting compound phenylthiocarbamide (PTC) which determines bitter “taster” and “non-taster” status in humans. Rambouillet and Targhee rams (n = 26) were offered various concentrations of PTC solution (0.2–12.29 mM) and water in a side-by-side presentation during two experiments. Blood was collected for DNA isolation and sequencing. Nineteen TAS2R genes were amplified and sequenced with long read Oxford Nanopore MinION technology. A total of 1,049 single nucleotide polymorphisms (SNPs) and 26 haplotypes were identified in these genes. Of these, 24 SNPs and 11 haplotypes were significantly (P < 0.05) associated with PTC consumption in TAS2R3, TAS2R5, TAS2R8, TAS2R9, TAS2R16, TAS2R31-like, TAS2R38, TAS2R39, and TAS2R42-like. Over 50% of the SNPs resulted in a change in amino acid sequence and several resided in potential regulatory regions, which could have downstream functional consequences and influence bitter taste perception in sheep. Further research is needed to validate these associations and elucidate the mechanisms that link variation in TAS2R genes to bitter taste perception in sheep. This may enable producers to select sheep more likely to consume bitter forage such as sagebrush as a flock and rangeland management strategy.

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.

Regional Variation of Bitter Taste and Aftertaste in Humans

Despite widespread and persistent myths of a tongue map, all 5 prototypical taste qualities are sensed over the entire tongue. However, modern psychophysical data also suggest there may be more nuanced differences in suprathreshold intensity across oral loci, especially for bitterness. Here, we test whether bitter stimuli matched for whole-mouth intensity differ in perceived intensity across regions of the oral cavity in 2 experiments. Experiment 1 consisted of a whole-mouth sip and spit approach and Experiment 2 consisted of a spatial taste test using cotton swabs. In Experiment 1, participants (n = 63) rated overall intensity of 3 bitter solutions at 5 different loci (front, middle, back of tongue; roof of mouth; and lip). Temporal effects were explored using in-mouth and aftertaste ratings. In Experiment 2, participants (n = 48) rated the intensity of quinine and Tetralone solutions after solutions were painted on fungiform, circumvallate, and foliate papillae with a swab. After the spatial taste test, participants completed a questionnaire on self-reported beer intake. Analysis of variance results of both experiments show a significant locus by stimulus interaction, suggesting different bitterants were perceived differently across the various loci. This result was apparently driven by low-intensity ratings for Tetralone on the anterior tongue. Aftertaste ratings in Experiment 1 also revealed significant temporal effects: ratings on the anterior tongue decreased for all bitterants and ratings for quinine decreased at all loci. Reasons for these effects are not known but may suggest differential expression of bitter taste receptors or differences in bitter agonist-receptor binding affinity across tongue regions.

Consumer-Based Sensory Characterization of Steviol Glycosides (Rebaudioside A, D, and M)

Rebaudioside (Reb) D and M are the recent focus of the food industry to address the bitter taste challenge of Reb A, which is the most commonly used steviol glycoside in natural sweetener stevia. This study evaluated the sensory characteristics of Reb A, D, and M, compared to 14% (w/v) sucrose, using a consumer panel and explored the relationship between 6-n-Propylthiouracil (PROP) taster status (i.e., non-tasters, medium tasters, supertasters) and the perceived intensity of sweet and bitter tastes of the three steviol glycosides. A total of 126 participants evaluated the intensities of in-mouth, immediate (5 s after expectorating), and lingering (1 min after expectorating) sweetness and bitterness of 0.1% Reb A, D, M, and 14% sucrose and described the aftertaste of the sweeteners by using a check-all-that-apply (CATA) question. The results showed that in-mouth sweetness and bitterness of Reb D and M were not significantly different from sucrose, unlike Reb A which showed significant bitterness. However, Reb D and M showed more intense lingering sweetness than sucrose. The CATA analysis resulted that Reb D and M were closer to positive attribute terms and also to sucrose than Reb A, but Reb D and M were still considered artificial, which may cause them to be perceived negatively. When comparing among PROP taster groups, no significant differences in the perceived sweetness and bitterness of the three steviol glycosides were found. This study generates important information about Reb A, D, and M for the food industry, especially working with products formulated to deliver reductions in sugar using a natural high-intensity sweetener, stevia.

Intense Sweeteners, Taste Receptors and the Gut Microbiome: A Metabolic Health Perspective

Intense sweeteners (IS) are often marketed as a healthier alternative to sugars, with the potential to aid in combating the worldwide rise of diabetes and obesity. However, their use has been counterintuitively associated with impaired glucose homeostasis, weight gain and altered gut microbiota. The nature of these associations, and the mechanisms responsible, are yet to be fully elucidated. Differences in their interaction with taste receptors may be a potential explanatory factor. Like sugars, IS stimulate sweet taste receptors, but due to their diverse structures, some are also able to stimulate bitter taste receptors. These receptors are expressed in the oral cavity and extra-orally, including throughout the gastrointestinal tract. They are involved in the modulation of appetite, glucose homeostasis and gut motility. Therefore, taste genotypes resulting in functional receptor changes and altered receptor expression levels may be associated with metabolic conditions. IS and taste receptors may both interact with the gastrointestinal microbiome, and their interactions may potentially explain the relationship between IS use, obesity and metabolic outcomes. While these elements are often studied in isolation, the potential interactions remain unexplored. Here, the current evidence of the relationship between IS use, obesity and metabolic outcomes is presented, and the potential roles for interactions with taste receptors and the gastrointestinal microbiota in modulating these relationships are explored.

Genetic Differences in Taste Receptors: Implications for the Food Industry

Inborn genetic differences in chemosensory receptors can lead to differences in perception and preference for foods and beverages. These differences can drive market segmentation for food products as well as contribute to nutritional status. This knowledge may be essential in the development of foods and beverages because the sensory profiles may not be experienced in the same way across individuals. Rather, distinct consumer groups may exist with different underlying genetic variations. Identifying genetic factors associated with individual variability can help better meet consumer needs through an enhanced understanding of perception and preferences. This review provides an overview of taste and chemesthetic sensations and their receptors, highlighting recent advances linking genetic variations in chemosensory genes to perception, food preference and intake, and health. With growing interest in personalized foods, this information is useful for both food product developers and nutrition health professionals alike.

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.

Chemosensory Changes from Cancer Treatment and Their Effects on Patients' Food Behavior: A Scoping Review

Individuals undergoing treatment for cancer can experience changes in taste or smell that are often assumed to affect constructs related to food behavior, although this relationship is rarely measured directly. To ascertain the extent to which measured changes in taste and smell during and after cancer treatment affect food behavior, we conducted a scoping review and completed a comparative analysis for studies that met our criteria, which were: they directly measured cancer patients’ (a) psychophysical response to taste and/or olfactory stimuli, and (b) food behavior (including food enjoyment, food preference, dietary intake) in people affected by cancer. Eleven studies met these criteria and were included in the review. All 11 studies evaluated taste and five also measured smell. A comparative analysis exploring taste and food behavior shows that a reduced sweet taste function (decreased sensitivity) was associated with a reduced intake of a variety of different macro and micro nutrients, reduced appetite, and overall lower energy intake. One out of six studies that measured smell and food measured observed changes in olfactory function following cancer treatment. There were no significant relationships reported between olfactory measures and food behavior. Taste changes that arise from cancer treatment appear to have a direct effect on food behavior, although there is a need for more research using standardized measures and larger sample sizes. A better understanding of taste alterations and their implications for dietary intake and food enjoyment will support optimal nutritional health by identifying strategies to help patients eat well during and after cancer treatment.

Sweet taste receptor agonists alter ovarian functions and ovarian cycles in aged mice

Saccharine sodium and rebaudioside A are low-calorie sweeteners, and the biologic effects of these sweeteners in rat ovaries are related to the activity of sweet taste receptors. Data on the impact and regulatory mechanisms underlying such sweeteners on the reproduction of aged animals are currently lacking. In the present study we assessed how the consumption of sweeteners affects the ovarian cycle, ovulation, biochemical indices, and other biologic functions. Thirty-six 1-year-old mice were randomly divided into 3 groups: a control (C) group receiving regular water, a saccharin sodium group receiving a 7.5 mM solution, and the rebaudioside A group receiving a 2.5 mM solution for 30 days. We observed no significant changes in body weights in any group. However, uterine weight in the rebaudioside A group significantly increased in diestrus, and we recorded a significant increase in the percentage of abnormal estrous cycles and the number of corpora lutea in the treatment groups. TUNEL staining and Immunoreactivity for the apoptosis-inducing factor (AIF) confirmed apoptosis in granulosa cells, oocyte, and corpus luteum. Serum glucose increased significantly in both treatment groups and there was a significant increase in cholesterol in the rebaudioside A group. Furthermore, the saccharin sodium-treated group exhibited elevated serum progesterone levels compared with the other groups. In conclusion, sweeteners manifested deleterious effects on reproductive indices in aged mice.

Complex relationship between TAS2 receptor variations, bitterness perception, and alcohol consumption observed in a population of wine consumers

Our ability to taste bitterness affects our food choices and alcohol consumption. Alleles in the taste 2 receptor member TAS2R38 have been linked to the ability to perceive bitterness in bitter-tasting compounds and in many foods, and people with these bitterness sensitivity alleles have been shown to be less likely to consume alcohol, presumably because of alcohol's bitter taste. In a survey of 519 participants, almost all of whom regularly consumed alcohol, we observed that genetic variants in TAS2R38 were significantly associated with both increased alcohol consumption and the ability to perceive bitterness in several foods and a bitter chemical. In total, we assayed 39 variants in 25 genes that have been implicated in the genetics of taste perception, and no other variants predicted alcohol consumption. Perception of bitterness in broccoli and a preference for black coffee were also positively associated with alcohol consumption. As the consumption of alcohol is a social activity there may be incentive to appreciate its bitter aspects, and increased perception of bitterness could therefore be associated with consumption of some bitter beverages. As this study's respondents were predominantly frequent consumers of alcohol, these findings may be consistent with previous studies that have seen that increased experience in the consumption of wine is associated with an increased perception of PROP bitterness. Further work elucidating the complex relationship between the genetics of bitter perception and alcohol consumption will better describe these connections.

A Pharmacological Perspective on the Study of Taste

The study of taste has been guided throughout much of its history by the conceptual framework of psychophysics, where the focus was on quantification of the subjective experience of the taste sensations. By the mid-20th century, data from physiologic studies had accumulated sufficiently to assemble a model for the function of receptors that must mediate the initial stimulus of tastant molecules in contact with the tongue. But the study of taste as a receptor-mediated event did not gain momentum until decades later when the actual receptor proteins and attendant signaling mechanisms were identified and localized to the highly specialized taste-responsive cells of the tongue. With those discoveries a new opportunity to examine taste as a function of receptor activity has come into focus. Pharmacology is the science designed specifically for the experimental interrogation and quantitative characterization of receptor function at all levels of inquiry from molecules to behavior. This review covers the history of some of the major concepts that have shaped thinking and experimental approaches to taste, the seminal discoveries that have led to elucidation of receptors for taste, and how applying principles of receptor pharmacology can enhance understanding of the mechanisms of taste physiology and perception.

Oral Post-Oral Actions of Low-Calorie Sweeteners: A Tale of Contradictions and Controversies

OBJECTIVE

Many scientists and laypeople alike have concerns about low-calorie sweeteners (LCSs). These concerns stem from both a dissatisfaction with the taste of LCSs and reports that they cause metabolic disruptions (e.g., weight gain, glucose intolerance).

METHODS

This article provides a critical review of the literature on LCSs from the standpoint of their taste, gastrointestinal, and metabolic effects; biological fate in the body; and impact on ingestion and glucose homeostasis.

RESULTS AND CONCLUSIONS

Mammals can readily discriminate between LCSs and sugars because both types of sweetener activate distinct oral and post-oral sensory pathways. LCSs differ in their ability to access post-oral tissues, but few studies have incorporated this observation into their design. It is difficult to extrapolate results between mice, rats, and humans because of interspecies differences in the taste and post-oral actions of LCSs and the fact that investigators often use different response measures in rodents and humans. There is confounding in the experimental design of some of the most widely cited studies of LCS-induced metabolic disruptions. The uncritical acceptance of these studies has generated considerable controversy. More work is needed to obtain a clearer understanding of the metabolic effects of LCSs.

Self-reported Smoking Status, TAS2R38 Variants, and Propylthiouracil Phenotype: An Exploratory Crowdsourced Cohort Study

TAS2R38 gene variants, which confer sensitivity to specific bitter tastants (e.g., 6-n-propylthiouracil), have been repeatedly associated with lower alcohol use via greater bitterness perception, but research exploring TAS2R38 variation in relation to smoking shows mixed results. In both, the working hypothesis is that 1 or more copies of the functional allele increases bitterness and may provide a barrier to early use. Such a barrier to initiation may, conceivably, manifest as differential rates of current use across diplotypes. Here, an age-diverse convenience sample (n = 886) of Denver Museum of Nature and Science guests was used to explore cross-sectional relationships between TAS2R38 diplotype, self-reported tobacco use (current, former, never smokers), and a rapid measure of 6-n-propylthiouracil phenotype (bitterness of filter paper discs). TAS2R38 diplotypes were determined by Sanger sequencing. After excluding rare diplotypes, data from 814 participants were analyzed. A mix of current (~10%), former (25%), and never smokers (65%) were included. As expected, there was a relationship between TAS2R38 diplotype and 6-n-propylthiouracil bitterness. However, contrary to our hypothesis, there was no evidence of a relationship between diplotype and smoker status among participants with common TAS2R38 diplotypes. Notably, we observed a relationship between of 6-n-propylthiouracil bitterness and smoking status, but the effect was opposite of what was expected: current smokers perceived higher (not lower) bitterness than never smokers. When all the various factors (diplotype, age, sex, and smoking status) were included in ANOVA, all remained predictive of 6-n-propylthiouracil bitterness. Reasons for greater phenotypic bitterness among current smokers are unknown and merit further study.

Taste Exam: A Brief and Validated Test

The emerging importance of taste in medicine and biomedical research, and new knowledge about its genetic underpinnings, has motivated us to supplement classic taste-testing methods in two ways. First, we explain how to do a brief assessment of the mouth, including the tongue, to ensure that taste papillae are present and to note evidence of relevant disease. Second, we draw on genetics to validate taste test data by comparing reports of perceived bitterness intensity and inborn receptor genotypes. Discordance between objective measures of genotype and subjective reports of taste experience can identify data collection errors, distracted subjects or those who have not understood or followed instructions. Our expectation is that fast and valid taste tests may persuade researchers and clinicians to assess taste regularly, making taste testing as common as testing for hearing and vision. Finally, because many tissues of the body express taste receptors, taste responses may provide a proxy for tissue sensitivity elsewhere in the body and, thereby, serve as a rapid, point-of-care test to guide diagnosis and a research tool to evaluate taste receptor protein function.

Use of Adult Sensory Panel to Study Individual Differences in the Palatability of a Pediatric HIV Treatment Drug

PURPOSE

The recommended first-line treatment for young children infected with HIV includes the liquid formulation of the co-formulated protease inhibitors lopinavir/ritonavir (Kaletra® [Abbott Laboratories, Chicago, Illinois]). Clinical reports indicate that some children readily accept the taste of Kaletra, whereas others strongly reject it, which can deter therapeutic adherence and outcomes.

METHODS

As a proof-of-concept approach, a sensory panel of genotyped adults was used to document the range of individual differences in the taste and palatability (hedonics) of the liquid formulation of Kaletra and other taste stimuli, including common excipients. Panelists rated taste sensations using generalized labeled magnitude scales to determine genotype-phenotype relationships. Several months later, the panelists were retested to assess response reliability.

FINDINGS

Not all panelists had the same sensory experience when tasting Kaletra. Palatability ratings varied widely, from moderate like to strongest imaginable dislike, and were reliable over time. The more irritating and bitter Kaletra tasted, the more disliked by the panelist. The more they disliked the taste of Kaletra, the more they disliked the taste of its excipient ethanol and the bitter stimulus denatonium. Those who experienced less bitter and sweeter taste sensations had a different genetic signature than the other panelists. Bitterness and irritation ratings of Kaletra varied by the orphaned bitter receptor gene (TAS2R60), whereas sweetness ratings of Kaletra varied according to the cold receptor gene (TRPM8), which is activated by menthol, an excipient of Kaletra. Neither genotype related to ratings for ethanol or denatonium, however.

IMPLICATIONS

The use of a sensory panel holds promise as a first step in determining the nature of individual differences in the palatability of existing pediatric drug formulations and sources of variation. In this era of personalized medicine, the need is great to develop psychophysical tools to determine which drugs will show variation in acceptance by children and whether patterns of individual variation in taste as assessed by adults mirror those of young patients. ClinicalTrials.gov identifier: NCT01841710.

Characterizing Dynamic Sensory Properties of Nutritive and Nonnutritive Sweeteners with Temporal Check-All-That-Apply

Temporal Check-All-That-Apply (TCATA) is a rapid method where attributes are actively checked and unchecked to track sensations over time, so that the checked words fully describe the sample in any given moment. Here, we characterize the temporal profiles of sweeteners using TCATA. In two experiments, sweeteners were tested in water at concentrations known to elicit weak to moderate sweetness. Before evaluating the sweeteners, participants (n= ~125 per experiment) were familiarized with the TCATA method with a guided example using imaginary samples of Kool-Aid. Participants then received 10 ml of each sweetener solution and were instructed to click "start" after he or she finished swallowing the sample. Incidence of 6 attributes obtained from prior literature - sweet, bitter, metallic, licorice, cooling, and drying - was obtained for 60s. We observed similarities across temporal profiles of various sweeteners: sweet and bitter occurred first (~10s), then metallic and cooling (~10-25s), followed by drying much later (30-50s depending on the stimulus). The presence of side tastes influenced how often 'sweet' was endorsed: stimuli with fewer endorsements of side tastes showed more prominent sweetness. Finally, unfamiliar side tastes may lead to a smearing bias where participants check every attribute in an attempt to characterize those unfamiliar sensations.

Variation in the TAS2R31 bitter taste receptor gene relates to liking for the nonnutritive sweetener Acesulfame-K among children and adults

The nonnutritive sweetener (NNS) acesulfame potassium (Ace-K) elicits a bitter off-taste that varies among adults due to polymorphisms in a bitter taste receptor gene. Whether polymorphisms affect liking for Ace-K by children, who live in different sensory worlds, is unknown. We examined hedonic response to Ace-K among children compared to adults, and whether response was related to common variants of the TAS2R31 bitter taste receptor gene and to NNS intake. Children (N = 48) and their mothers (N = 34) rated liking of Ace-K, and mothers reported whether they or their children ever consume NNSs via questionnaire. Participants were genotyped for TAS2R31 variant sites associated with adult perception of Ace-K (R35W, L162M, A227V, and V240I). Regardless of age, more participants with 1 or no copies than with 2 copies of the TAS2R31 WMVI haplotype liked Ace-K (p = 0.01). NNS-sweetened products were consumed by 50% and 15% of mothers and children, respectively, with no association between intake and TAS2R31. The TAS2R31 WMVI haplotype was partly responsible for children’s hedonic response to Ace-K, highlighting a potential role for inborn differences in vulnerability to overconsumption of Ace-K-containing products. Currently available methods to measure NNS intake yield crude estimates at best, suggesting self-reports are not reflective of actual intake.

Differences in food intake and genetic variability in taste receptors between Czech pregnant women with and without gestational diabetes mellitus

PURPOSE

Gestational diabetes mellitus (GDM) represents the most frequent metabolic disorder in pregnancy. Since dietary intake plays an important role in obesity and type 2 diabetes development, it is likely to be for the susceptibility to GDM too. Food preferences, driving partly the diet composition, are changing during pregnancy. Taste and genetic variability in taste receptors is an important factor in determining food preferences. Aims of our study were (1) to characterize dietary habits of pregnant women and to find possible differences in food preferences between healthy pregnant women and those with GDM and (2) to ascertain possible association of several single nucleotide polymorphisms (SNPs) in taste receptor (TR) genes with GDM.

METHODS

A total of 363 pregnant women (293 with GDM and 70 with physiologic pregnancy) were included in the study. Dietary pattern spanning the period of approx. 6 months preceding the time of GDM screening was assessed using a semi-quantitative food frequency questionnaire. A total of five SNPs in TR genes were selected for genotyping based on their functionality or previous associations.

RESULTS

Women with GDM exhibited significantly more frequent meat consumption (esp. poultry, pork and smoked meat), dairy products and sweet beverages consumption. The legumes consumption was found to be inversely correlated with fasting glycaemia (P = 0.007, Spearman). CC genotype in TAS2R9 gene (SNP rs3741845) was significantly associated with GDM (P = 0.0087, Chi-square test).

CONCLUSIONS

Our study showed differences in dietary intake of selected food items between healthy pregnant women and those with GDM and genetic association of bitter taste receptor allele with GDM.

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.

Polymorphisms in sweet taste genes (TAS1R2 and GLUT2), sweet liking, and dental caries prevalence in an adult Italian population

The aim of the study was to assess the relationship between sweet taste genes and dental caries prevalence in a large sample of adults. In addition, the association between sweet liking and sugar intake with dental caries was investigated. Caries was measured by the decayed, missing, filled teeth (DMFT) index in 647 Caucasian subjects (285 males and 362 females, aged 18-65 years), coming from six villages in northeastern Italy. Sweet liking was assessed using a 9-point scale, and the mean of the liking given by each individual to specific sweet food and beverages was used to create a sweet liking score. Simple sugar consumption was estimated by a dietary history interview, considering both added sugars and sugar present naturally in foods. Our study confirmed that polymorphisms in TAS1R2 and GLUT2 genes are related to DMFT index. In particular, GG homozygous individuals for rs3935570 in TAS1R2 gene (p value = 0.0117) and GG homozygous individuals for rs1499821 in GLUT2 gene (p value = 0.0273) showed higher DMFT levels compared to both heterozygous and homozygous for the alternative allele. Furthermore, while the relationship sugar intake-DMFT did not achieve statistical significance (p value = 0.075), a significant association was identified between sweet liking and DMFT (p value = 0.004), independent of other variables. Our study showed that sweet taste genetic factors contribute to caries prevalence and highlighted the role of sweet liking as a predictor of caries risk. Therefore, these results may open new perspectives for individual risk identification and implementation of target preventive strategies, such as identifying high-risk patients before caries development.

Bitter taste genetics--the relationship to tasting, liking, consumption and health

Bitter is the most complex of human tastes, and is arguably the most important. Aversion to bitter taste is important for detecting toxic compounds in food; however, many beneficial nutrients also taste bitter and these may therefore also be avoided as a consequence of bitter taste. While many polymorphisms in TAS2R genes may result in phenotypic differences that influence the range and sensitivity of bitter compounds detected, the full extent to which individuals differ in their abilities to detect bitter compounds remains unknown. Simple logic suggests that taste phenotypes influence food preferences, intake and consequently health status. However, it is becoming clear that genetics only plays a partial role in predicting preference, intake and health outcomes, and the complex, pleiotropic relationships involved are yet to be fully elucidated.

Gender differences in the influence of personality traits on spicy food liking and intake

It has been proposed, and only minimally explored, that personality factors may play a role in determining an individual's sensitivity to and preference for capsaicin containing foods. We explored these relationships further here. Participants rated a number of foods and sensations on a generalized liking scale in a laboratory setting; after leaving the laboratory, they filled out an online personality survey, which included Arnett's Inventory of Sensation Seeking (AISS) and the Sensitivity to Punishment-Sensitivity to Reward Questionnaire (SPSRQ). Recently, we reported strong and moderate correlations between the liking of a spicy meal and the personality constructs of Sensation Seeking (AISS) and Sensitivity to Reward (SPSRQ), respectively. Here, we use moderation models to explore the relationships between personality traits, perceived intensity of the burn of capsaicin, and the liking and consumption of spicy foods. Limited evidence of moderation was observed; however differential effects of the personality traits were seen in men versus women. In men, Sensitivity to Reward associated more strongly with liking and consumption of spicy foods, while in women, Sensation Seeking associated more strongly with liking and intake of spicy foods. These differences suggest that in men and women, there may be divergent mechanisms leading to the intake of spicy foods; specifically, men may respond more to extrinsic factors, while women may respond more to intrinsic factors.

Quinine Bitterness and Grapefruit Liking Associate with Allelic Variants in TAS2R31

Multiple psychophysical gene-association studies suggest a single nucleotide polymorphism (SNP) within the bitter receptor gene TAS2R19 on chromosome 12 may be functional. Previously, the Arg299Cys SNP (rs10772420) has been associated with differential bitterness of quinine and differential liking for grapefruit juice. However, quinine does not activate TAS2R19 in vitro; likewise, limonin and naringin, bitter compounds in grapefruit, do not activate TAS2R19 in vitro. Here, we examined quinine bitterness (whole-mouth swish-and-spit stimuli and regionally delivered quinine across 4 loci) and remembered liking for grapefruit juice to test whether they associate with SNPs in another nearby gene, TASR2R31. We observed SNP-phenotype associations between whole-mouth quinine bitterness and self-reported liking for grapefruit juice with SNPs in TAS2R31, and regional quinine bitterness followed a similar trend, but did not reach significance. Present data provide independent replication of prior associations reported for TAS2R19. However, we also observed strong linkage disequilibrium (LD) between TAS2R19 and TAS2R31 SNPs. When present data are considered in light of existing functional expression data, this suggests phenotypic associations reported previously for rs10772420 may potentially be due to LD between this SNP and polymorphism(s) in, or closer to, TAS2R31. If confirmed, this would reduce the number of TAS2Rs with putatively functional polymorphisms to 5.

Variability in Human Bitter Taste Sensitivity to Chemically Diverse Compounds Can Be Accounted for by Differential TAS2R Activation

The human population displays high variation in taste perception. Differences in individual taste sensitivity may also impact on nutrient intake and overall appetite. A well-characterized example is the variable perception of bitter compounds such as 6-n-propylthiouracil (PROP) and phenylthiocarbamide (PTC), which can be accounted for at the molecular level by polymorphic variants in the specific type 2 taste receptor (TAS2R38). This phenotypic variation has been associated with influencing dietary preference and other behaviors, although the generalization of PROP/PTC taster status as a predictor of sensitivity to other tastes is controversial. Here, we proposed that the taste sensitivities of different bitter compounds would be correlated only when they activate the same bitter taste receptor. Thirty-four volunteers were exposed to 8 bitter compounds that were selected based on their potential to activate overlapping and distinct repertoires of TAS2Rs. Taste intensity ratings were evaluated using the general Labeled Magnitude Scale. Our data demonstrate a strong interaction between the intensity for bitter substances when they activate common TAS2Rs. Consequently, PROP/PTC sensitivity was not a reliable predictor of general bitter sensitivity. In addition, our findings provide a novel framework to predict taste sensitivity based on their specific T2R activation profile.

Nonnutritive sweeteners are not supernormal stimuli

BACKGROUND

It is often claimed that nonnutritive sweeteners (NNS) are 'sweeter than sugar', with the implicit implication that high-potency sweeteners are supernormal stimuli that encourage exaggerated responses. This study aimed to investigate the perceived sweetness intensity of a variety of nutritive sweeteners (sucrose, maple syrup and agave nectar) and NNS (acesulfame-K (AceK), rebaudioside A (RebA), aspartame and sucralose) in a large cohort of untrained participants using contemporary psychophysical methods.

METHODS

Participants (n=401 total) rated the intensity of sweet, bitter and metallic sensations for nutritive sweeteners and NNS in water using the general labeled magnitude scale.

RESULTS

Sigmoidal dose-response functions were observed for all stimuli except AceK. That is, sucrose follows a sigmoidal function if the data are not artifactually linearized via prior training. More critically, there is no evidence that NNS have a maximal sweetness (intensity) greater than sucrose; indeed, the maximal sweetness for AceK, RebA and sucralose were significantly lower than that for concentrated sucrose. For these sweeteners, mixture suppression due to endogenous dose-dependent bitter or metallic sensations appears to limit maximal perceived sweetness.

CONCLUSIONS

In terms of perceived sweetness, NNS cannot be considered supernormal stimuli. These data do not support the view that NNS hijack or overstimulate sweet receptors to produce elevated sweet sensations.

Physical approaches to masking bitter taste: lessons from food and pharmaceuticals

Many drugs and desirable phytochemicals are bitter, and bitter tastes are aversive. Food and pharmaceutical manufacturers share a common need for bitterness-masking strategies that allow them to deliver useful quantities of the active compounds in an acceptable form and in this review we compare and contrast the challenges and approaches by researchers in both fields. We focus on physical approaches, i.e., micro- or nano-structures to bind bitter compounds in the mouth, yet break down to allow release after they are swallowed. In all of these methods, the assumption is the degree of bitterness suppression depends on the concentration of bitterant in the saliva and hence the proportion that is bound. Surprisingly, this hypothesis has only rarely been fully tested using a combination of adequate human sensory trials and measurements of binding. This is especially true in pharmaceutical systems, perhaps due to the greater experimental challenges in sensory analysis of drugs.

TAS2R bitter taste receptors regulate thyroid function

Dysregulation of thyroid hormones triiodothyronine and thyroxine (T3/T4) can impact metabolism, body composition, and development. Thus, it is critical to identify novel mechanisms that impact T3/T4 production. We found that type 2 taste receptors (TAS2Rs), which are activated by bitter-tasting compounds such as those found in many foods and pharmaceuticals, negatively regulate thyroid-stimulating hormone (TSH)-dependent Ca(2+) increases and TSH-dependent iodide efflux in thyrocytes. Immunohistochemical Tas2r-dependent reporter expression and real-time PCR analyses reveal that human and mouse thyrocytes and the Nthy-Ori 3-1 human thyrocyte line express several TAS2Rs. Five different agonists for thyrocyte-expressed TAS2Rs reduced TSH-dependent Ca(2+) release in Nthy-Ori 3-1 cells, but not basal Ca(2+) levels, in a dose-dependent manner. Ca(2+) responses were unaffected by 6-n-propylthiouracil, consistent with the expression of an unresponsive variant of its cognate receptor, TAS2R38, in these cells. TAS2R agonists also inhibited basal and TSH-dependent iodide efflux. Furthermore, a common TAS2R42 polymorphism is associated with increased serum T4 levels in a human cohort. Our findings indicate that TAS2Rs couple the detection of bitter-tasting compounds to changes in thyrocyte function and T3/T4 production. Thus, TAS2Rs may mediate a protective response to overingestion of toxic materials and could serve as new druggable targets for therapeutic treatment of hypo- or hyperthyroidism.

Polymorphisms in TRPV1 and TAS2Rs associate with sensations from sampled ethanol

BACKGROUND

Genetic variation in chemosensory genes can explain variability in individual's perception of and preference for many foods and beverages. To gain insight into variable preference and intake of alcoholic beverages, we explored individual variability in the responses to sampled ethanol (EtOH). In humans, EtOH elicits sweet, bitter, and burning sensations. Here, we explore the relationship between variation in EtOH sensations and polymorphisms in genes encoding bitter taste receptors (TAS2Rs) and a polymodal nociceptor (TRPV1).

METHODS

Caucasian participants (n = 93) were genotyped for 16 single nucleotide polymorphisms (SNPs) in TRPV1, 3 SNPs in TAS2R38, and 1 SNP in TAS2R13. Participants rated sampled EtOH on a generalized Labeled Magnitude Scale. Two stimuli were presented: a 16% EtOH whole-mouth sip-and-spit solution with a single time-point rating of overall intensity and a cotton swab saturated with 50% EtOH on the circumvallate papillae (CV) with ratings of multiple qualities over 3 minutes. Area-under-the-curve (AUC) was calculated for the time-intensity data.

RESULTS

The EtOH whole-mouth solution had overall intensity ratings near "very strong." Burning/stinging had the highest mean AUC values, followed by bitterness and sweetness. Whole-mouth intensity ratings were significantly associated with burning/stinging and bitterness AUC values on the CV. Three TRPV1 SNPs (rs224547, rs4780521, rs161364) were associated with EtOH sensations on the CV, with 2 (rs224547 and rs4780521) exhibiting strong linkage disequilibrium. Additionally, the TAS2R38 SNPs rs713598, rs1726866, and rs10246939 formed a haplotype, and were associated with bitterness on the CV. Last, overall intensity for whole-mouth EtOH associated with the TAS2R13 SNP rs1015443.

CONCLUSIONS

These data suggest genetic variation in TRPV1 and TAS2Rs influence sensations from sampled EtOH and may potentially influence how individuals initially respond to alcoholic beverages.

Regional differences in suprathreshold intensity for bitter and umami stimuli

The sense of taste is often referred to as a 'nutritional gatekeeper', thought to have evolved to indicate energy sources and prevent ingestion of potential toxins. Fungiform papillae are structures on the anterior tongue in which taste buds are situated. They are concentrated at the tongue's tip and they can provide a useful estimate of overall taste bud density for taste research. Some reports suggest taste perception may differ subtly across tongue regions, irrespective of FP number. Other data show an association between taste intensity perception for the bitter compound 6-n-propylthiouracil (PROP) and FP density. However, contradictions exist in the literature, with more recent, larger studies suggesting little or no association between FP number and perceived taste intensity. Much research has examined the relation between FP density and PROP perception, while other tastes have been less thoroughly studied. Here, in a cohort of mainly Caucasian individuals, aged 18-45, recruited from the campus of a large rural university, we examined regional and whole-mouth taste intensities, and FP density using an updated method of a digital still photography method first described in 2005. We found regional differences in suprathreshold intensity. Although all taste sensations were experienced all over the tongue, once again disproving the mythical tongue map, we also observed bitter and umami taste perception to be significantly greater on the posterior tongue than on the anterior tongue. In contrast, there were no regional differences observed for sweet, salty or sour tastes. The relation of FP density to whole-mouth intensity of 6-n-propylthiouracil, and to the intensity of saltiness of NaCl, sweetness from sucrose or from Acesulfame-K, bitterness of quinine, or burning from capsaicin delivered to different regions of the tongue are also discussed.

Genetic signature of differential sensitivity to stevioside in the Italian population

The demand for diet products is continuously increasing, together with that for natural food ingredients. Stevioside and other steviol glycosides extracted from the leaves of the plant Stevia rebaudiana Bertoni are the first natural high-potency sweeteners to be approved for consumption in the United States and the European Union. However, the sweetness of these compounds is generally accompanied by aversive sensations, such as bitter and off-tastes, which may constitute a limit to their consumption. Moreover, consumers' differences in sensitivity to high-potency sweeteners are well known, as well as difficulties in characterizing their aftertaste. Recently, TAS2R4 and TAS2R14 have been identified as the receptors that mediate the bitter off-taste of steviol glycosides in vitro. In the present study, we demonstrate that TAS2R4 gene polymorphism rs2234001 and TAS2R14 gene polymorphism rs3741843 are functional for stevioside bitterness perception.

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

Recent reports suggest that polymorphisms in the carbonic anhydrase gene CA6 (also known as gustin) may explain additional variation in the bitterness of 6-n-propylthiouracil beyond that explained by variation in the bitter receptor gene TAS2R38. CA6 (gustin) has been implicated in taste bud function and salivary buffer capacity. In the present study we examined associations between polymorphisms in the CA6 gene with salt and bitter taste perception, and oral anatomy. 243 subjects (146 female) aged 18-45 rated the intensity of five concentrations of 6-n-propylthiouracil and NaCl on a generalized Labeled Magnitude Scale (gLMS) in duplicate and one concentration of potassium chloride (KCl). Using salivary DNA, we examined 12 SNPs within CA6 in relation to taste intensity and number of fungiform papillae. We observed no difference in bitter taste perception from 6-n-propylthiouracil (PROP) or from potassium chloride for any of the SNPs examined. Perceived saltiness of NaCl on the other hand was significantly associated with a number of CA6 polymorphisms, and particularly rs3737665. Nonetheless, FP density did not vary between alleles of rs3737665, nor with any of the other CA6 SNPs. Also, we fail to find any evidence that CA6 effects on taste perception are due to differences in fungiform papilla number. Additional work is needed to confirm whether variations within the CA6 gene may be responsible for differences in salt taste perception.