Validation of edible taste strips for assessing PROP taste perception

TAS2R38 haplotypes, COVID-19 infection, and symptomatology: a cross-sectional analysis of data from the Canadian Longitudinal Study on Aging

The TAS2R38 gene is well known for its function in bitter taste sensitivity, but evidence also suggests a role in innate immunity. TAS2R38 may be relevant in coronavirus disease 2019 (COVID-19), but research findings are inconsistent. The objective of this study was to explore whether common TAS2R38 haplotypes are associated with COVID-19 infection and symptomatology in the Canadian Longitudinal Study on Aging (CLSA). Data from the CLSA COVID-19 Questionnaire and Seroprevalence sub-studies were utilized with CLSA genetic data for common TAS2R38 haplotypes related to bitter taste sensitivity. Haplotypes were categorized into three diplotype groups: [P]AV homozygotes, [P]AV/[A]VI heterozygotes, and [A]VI homozygotes. No significant differences were observed between diplotypes and COVID-19 infection frequency. Among self-reported COVID-19 cases (n = 76), and in uncorrected exploratory analyses, heterozygotes were less likely to report experiencing sinus pain compared to [P]AV homozygotes. Among seroprevalence-confirmed cases (n = 177), [A]VI homozygotes were less likely to report experiencing a sore/scratchy throat compared to [P]AV homozygotes. However, both observations were non-significant upon correction for multiple testing. In this study, TAS2R38 haplotypes were not significantly associated with COVID-19 infection or symptomatology. Nevertheless, in light of some exploratory patterns and conflicting evidence, additional research is warranted to evaluate links between TAS2R38 and innate immunity.

Comparing Taste Perception Across Modalities in Healthy Adults: Liquids Versus Dissolvable Taste Strips

Taste stimulation has rehabilitative value in dysphagia management, as it activates salient underlying afferent pathways to swallowing which may evoke feedforward effects on swallow biomechanics. Despite its potential beneficial effects on swallow physiology, taste stimulation's clinical application is limited for persons unsafe to orally consume food/liquid. This study aimed to create edible, dissolvable taste strips matched to flavor profiles previously used in research assessing taste's effects on swallowing physiology and brain activity, and to evaluate how similar their perceived intensity and hedonic, or palatability, ratings were between their liquid counterparts. Plain, sour, sweet-sour, lemon, and orange flavor profiles were custom-made in taste strips and liquid modalities. The generalized Labeled Magnitude Scale and hedonic generalized Labeled Magnitude Scale were used to assess intensity and palatability ratings for flavor profiles in each modality. Healthy participants were recruited and stratified across age and sex. Liquids were rated as more intense than taste strips; however, there was no difference in palatability ratings between the modalities. There were significant differences across flavor profiles in intensity and palatability ratings. Collapsed across liquid and taste strip modalities, pairwise comparisons revealed all flavored stimuli were rated as more intense than the plain profile, sour was perceived as more intense and less palatable than all other profiles, and orange was rated as more palatable than sour, lemon, and plain tastants. Taste strips have useful implications for dysphagia management, as they could offer safe and patient-preferred flavor profiles to potentially provide advantageous swallowing and neural hemodynamic responses.

Differential effects of nutritive and non-nutritive sweet mouth rinsing on appetite in adults with obesity

BACKGROUND

Excessive added sugar intake has been associated with obesity; however, the effect of dietary sweetness on energy intake (EI) and appetite in adults with and without obesity has not yet been determined.

OBJECTIVE

To assess the effect of mouth rinses with and without energy and sweetness on measures of appetite, and to compare responses between subjects with body mass index (BMI) between 18.5 and 24.9 kg/m2 or ≥30 kg/m2.

METHODS

In this randomized, double-blind crossover study, 39 subjects (age 23±5y; 17 male, 22 female; BMI 18.5-24.9 kg/m2: n = 21; ≥30 kg/m2: n = 18) performed modified sham-feeding (MSF) with a mouth rinse containing either sucrose, sucralose, maltodextrin, or water for 2min before expectorating the solution. Blood sampling and subjective appetite assessments occurred at baseline (-5) and 15, 30, 60, and 90min post-MSF. After, EI was assessed at a buffet meal and post-meal appetite ratings were assessed hourly for 3h.

RESULTS

Post-MSF ghrelin increased for water vs. maltodextrin (water: p = 0.03). Post-MSF cholecystokinin increased following maltodextrin-MSF (p = 0.03) and sucralose-MSF (p = 0.005) vs. sucrose for those with BMI:18.5-24.9 kg/m2 only. There was greater post-MSF desire to eat in response to water vs. sucrose (p = 0.03) and reduced fullness with sucralose for those with BMI≥30 vs. 18.5-24.9 kg/m2 (p < 0.001). There was no difference in EI at the buffet meal by mouth rinse (p = 0.98) or by BMI (p = 0.12). However, there was greater post-meal fullness following sucralose-MSF vs. water (p = 0.03) and sucrose (p = 0.004) for those with BMI≥30 vs. 18.5-24.9 kg/m2.

CONCLUSION

Sucralose rinsing led to greater cephalic phase CCK release in adults with a BMI:18.5-24.9 kg/m2 only; however, ghrelin responses to unsweetened rinses were energy-specific for all adults. As subsequent EI was unaffected, further investigation of cephalic phase appetite is warranted.

Salivary microbial profiles associate with responsiveness to warning oral sensations and dietary intakes

Oral microbiota-host interactions are gaining recognition as potential factors contributing to interindividual variations in taste perception. However, whether such possible links imply specific bacterial co-occurrence networks remains unknown. To address this issue, we used 16 s rRNA gene sequencing to profile the salivary microbiota of 100 healthy individuals (52 % women; 18-30 y/o), who provided hedonic and psychophysical responses to 5 liquid and 5 solid commercially-available foods, each chosen to elicit a target sensation (sweet, sour, bitter, salty, pungent). The same cohort also completed several psychometric measures and a 4-day food diary. Unsupervised data-driven clustering of genus-level Aitchison distances supported the existence of two salivary microbial profiles (CL-1, CL-2). While CL-1 (n = 57; 49.1 % women) exhibited higher α-diversity metrics and was enriched in microbial genera assigned to the class Clostridia (e.g., Lachnospiraceae_[G-3]), CL-2 (n = 43; 55.8 % women) harbored greater amounts of taxa with potential cariogenic effects (e.g., genus Lactobacillus) and significantly lower abundances of inferred MetaCyc pathways related to the metabolic fate of acetate. Intriguingly, CL-2 showed enhanced responsiveness to warning oral sensations (bitter, sour, astringent) and a higher propensity to crave sweet foods or engage in prosocial behaviors. Further, the same cluster reported habitually consuming more simple carbohydrates and fewer beneficial nutrients (vegetable proteins, monounsaturated fatty acids). In summary, while the mediating role of participants' baseline diet on findings can not be definitively excluded, this work provides evidence suggesting that microbe-microbe and microbe-taste interactions may exert an influence on dietary habits and motivates further research to uncover a potential "core" taste-related salivary microbiota.

Brain activity associated with taste stimulation: A mechanism for neuroplastic change?

PURPOSE

Neuroplasticity may be enhanced by increasing brain activation and bloodflow in neural regions relevant to the target behavior. We administered precisely formulated and dosed taste stimuli to determine whether the associated brain activity patterns included areas that underlie swallowing control.

METHODS

Five taste stimuli (unflavored, sour, sweet-sour, lemon, and orange suspensions) were administered in timing-regulated and temperature-controlled 3 mL doses via a customized pump/tubing system to 21 healthy adults during functional magnetic resonance imaging (fMRI). Whole-brain analyses of fMRI data assessed main effects of taste stimulation as well as differential effects of taste profile.

RESULTS

Differences in brain activity associated with taste stimulation overall as well as specific stimulus type were observed in key taste and swallowing regions including the orbitofrontal cortex, insula, cingulate, and pre- and postcentral gyri. Overall, taste stimulation elicited increased activation in swallowing-related brain regions compared to unflavored trials. Different patterns of blood oxygen level-dependent (BOLD) signal were noted by taste profile. For most areas, sweet-sour and sour trials elicited increases in BOLD compared to unflavored trials within that region, whereas lemon and orange trials yielded reductions in BOLD. This was despite identical concentrations of citric acid and sweetener in the lemon, orange, and sweet-sour solutions.

CONCLUSIONS

These results suggest that neural activity in swallowing-relevant regions can be amplified with taste stimuli and may be differentially affected by specific properties within very similar taste profiles. These findings provide critical foundational information for interpreting disparities in previous studies of taste effects on brain activity and swallowing function, defining optimal stimuli to increase brain activity in swallowing-relevant regions, and harnessing taste to enhance neuroplasticity and recovery for persons with swallowing disorders.

The effect of taste on swallowing: A scoping and systematic review

Consuming foods and liquids for nutrition requires the coordination of several muscles. Swallowing is triggered and modified by sensory inputs from the aerodigestive tract. Taste has recently received attention as a potential modulator of swallowing physiology, function, and neural activation; additionally, taste impairment is a sequela of COVID-19. This review presents factors impacting taste and swallowing, systematically summarizes the existing literature, and assesses the quality of included studies. A search was conducted for original research including taste stimulation, deglutition-related measure(s), and human participants. Study design, independent and dependent variables, and participant characteristics were coded; included studies were assessed for quality and risk of bias. Forty-eight articles were included after abstract and full-text review. Synthesis was complicated by variable sensory components of stimuli (taste category and intensity, pure taste vs. flavor, chemesthesis, volume/amount, consistency, temperature), participant characteristics, confounding variables such as genetic taster status, and methods of measurement. Most studies had a high risk of at least one type of bias and were of fair or poor quality. Interpretation is limited by wide variability in methods, taste stimulation, confounding factors, and lower-quality evidence. Existing studies suggest that taste can modulate swallowing, but more rigorous and standardized research is needed.

Associations between chronic cigarette smoking and taste function: Results from the 2013-2014 national health and nutrition examination survey

We identified associations between cigarette-smoking and taste function in the U.S. NHANES 2013-2014. Adults ≥ 40 years (n = 2849, nearly half former or current smokers) rated whole-mouth and tongue-tip bitter (1 mM quinine) and salt (1 M NaCl, 0.32 M NaCl) intensities and reported smoking history (pack years, PY), dependence (time to first cigarette, TTFC) and menthol/non-menthol use. Perceived intensity on the tongue-tip averaged just below moderate for quinine and moderate to strong for 1 M NaCl. Current chronic smokers (≥ 20 PY) reported lower bitter and salty intensities on the tongue-tip (β: -2.0, 95% CI: -3.7 to -0.4 and β: -3.6, 95% CI: -6.9 to -0.3, respectively) than never smokers. Similarly, compared to never smokers, dependent current smokers (TTFC ≤ 30 min) and dependent chronic smokers (≥ 20 PY, TTFC ≤ 30 min) rated less bitter (β: -2.0, 95% CI: -4.0 to 0.1 and β: -2.9, 95% CI: -4.5 to -1.3, respectively) and salty (β: -5.3, 95% CI: -9.3 to -1.4 and β: -4.7, 95% CI: -8.6 to -0.7, respectively) intensities on the tongue-tip. Depressed tongue-tip intensity in dependent smokers (with/without chronicity) versus never smokers was significant in younger (40-65 years), but not older (> 65 years) adults. Former smokers, non-chronic/less dependent smokers, and menthol smokers were more likely to report elevated whole-mouth quinine and 1 M NaCl intensities. Tongue-tip and whole-mouth taste intensity concordance varied between smokers and never smokers-current dependent smokers were more likely to rate tongue-tip quinine and NaCl lower than their respective whole-mouth tastants (OR: 1.8, 95% CI: 1.0 to 3.1 and OR: 1.8, 95% CI: 1.1 to 2.8, respectively). In summary, these U.S. nationally-representative data show that current smoking with chronicity and/or dependence associates with lower tongue-tip intensity for bitter and salty stimuli. Smokers with greater exposure to nicotine and/or dependence showed greater risk of taste alterations, with implications for diet- and smoking-related health outcomes.

Chemosensory Function in Burning Mouth Syndrome a Comparative Cross-Sectional Study

Taste and smell are considered to be functions that contribute to the maintenance of good nutritional status. The present study evaluates taste and smell function in patients with burning mouth syndrome (BMS) versus a control group. A cross-sectional study was made of 36 consecutive patients with BMS and 56 healthy patients. Smell was assessed using the Sniffin' Sticks test, while taste was evaluated with Taste Strips. Oral quality of life was assessed with the Oral Health Impact Profile-14 (OHIP-14), and the severity of dry mouth with the Thompson Xerostomia Inventory. The patients with BMS had a mean age of 60.4 0 ± 10.5 years, while the controls had a mean age of 61.3 ± 19 years. No significant differences in smell were recorded between the two groups. In contrast, significant differences in taste function were observed between the patients with BMS and the controls. In the patients with BMS, 44.4% suffered taste alterations compared with the 3.4% healthy controls. Further studies in such patients are needed to allow improved management of the chemosensory problems, mouth dryness, and oral health-related quality of life in BMS.

Genetic Taster Status as a Mediator of Neural Activity and Swallowing Mechanics in Healthy Adults

As part of a larger study examining relationships between taste properties and swallowing, we assessed the influence of genetic taster status (GTS) on measures of brain activity and swallowing physiology during taste stimulation in healthy men and women. Twenty-one participants underwent videofluoroscopic swallowing study (VFSS) and functional magnetic resonance imaging (fMRI) during trials of high-intensity taste stimuli. The precisely formulated mixtures included sour, sweet-sour, lemon, and orange taste profiles and unflavored controls. Swallowing physiology was characterized via computational analysis of swallowing mechanics plus other kinematic and temporal measures, all extracted from VFSS recordings. Whole-brain analysis of fMRI data assessed blood oxygen responses to neural activity associated with taste stimulation. Swallowing morphometry, kinematics, temporal measures, and neuroimaging analysis revealed differential responses by GTS. Supertasters exhibited increased amplitude of most pharyngeal movements, and decreased activity in the primary somatosensory cortex compared to nontasters and midtasters. These preliminary findings suggest baseline differences in swallowing physiology and the associated neural underpinnings associated with GTS. Given the potential implications for dysphagia risk and recovery patterns, GTS should be included as a relevant variable in future research regarding swallowing function and dysfunction.

Development of a Regional Taste Test that uses Edible Circles for Stimulus Delivery

Introduction

Measurements of chemosensory function within specific regions of the tongue can yield important information about the sensitivity of lingual areas to chemosensory stimuli, and may identify possible nerve damage. A novel regional chemosensory test that uses thin edible circles was developed for human testing.

Methods

Edible circles placed at six different regions of the tongue were used to examine regional sensitivity to quinine for bitter taste, NaCl for salt taste, sucralose for sweet taste, and capsaicin for pungency. The six regions included the anterior tip of the tongue, the left and right lateral margins of the tongue (anterior and posterior), and the circumvallate region. Testing was completed with the mouth open, and the mouth closed.

Results

Intensity ratings at all sites were higher in the closed mouth condition for the three taste stimuli. Quinine intensity was highest at the circumvallate region with the mouth closed. NaCl and sucralose intensity were highest at the anterior tip and circumvallate regions. Capsaicin intensity was most highly perceived at the anterior tip of the tongue, but open and closed mouth intensity ratings showed no significant differences.

Conclusions

Regional differences in chemosensory perception were observed on the tongue, and these differences were dependent on the chemosensory stimulus, tongue region, and tasting mode.

Implications

Edible circles show minimal diffusion with saliva, can be used to examine both taste and irritation, and may be used to identify regional papillae counts on the tongue. Finally, edible circles should be invaluable for examining damage to the oral cavity.

Taste disorders are partly genetically determined: Role of the TAS2R38 gene, a pilot study

OBJECTIVES/HYPOTHESIS

Taste sensitivity varies greatly among individuals influencing eating behavior and health, consequently the disorders of this sense can affect the quality of life. The ability to perceive the bitter of thiourea compounds, such as phenylthiocarbamide (PTC), has been largely reported as a marker of the general taste sensitivity, food preferences, and health. PTC sensitivity is mediated by the TAS2R38 receptor and its genetic common variants. We study the role of the TAS2R38 receptor in taste disorders with the aim of understanding if these can be genetically determined.

STUDY DESIGN

Prospective cohort study.

METHODS

Differences in the PTC responsiveness between the patients cohort and healthy controls were assessed. All subjects received standardized tests for smell and taste function and were genotyped for the TAS2R38 gene.

RESULTS

PAV/PAV homozygous patients gave high PTC ratings, whereas PAV/AVI genotypes reported lower values, which are similar to those determined in AVI/AVI or rare genotypes. In addition, the patients cohort did not meet the Hardy-Weinberg equilibrium at the TAS2R38 locus, showing a very low frequency of subjects carrying the PAV/AVI diplotype. Independently, in healthy controls who were in equilibrium at the locus, PAV/PAV homozygous and heterozygous rated PTC bitterness higher compared to AVI/AVI or rare genotypes.

CONCLUSIONS

Our findings, by showing that an only taster haplotype (PAV) is not sufficient to evoke high responses of TAS2R38 receptor in patients with taste disorders, suggest that the genetic constitution may represent a risk factor for the development of taste disorders.

LEVEL OF EVIDENCE

2c Laryngoscope, 129:E307-E312, 2019.

Toward Improving Medication Adherence: The Suppression of Bitter Taste in Edible Taste Films

Bitter taste is aversive to humans, and many oral medications exhibit a bitter taste. Bitter taste can be suppressed by the use of inhibitors or by masking agents such as sucralose. Another approach is to encapsulate bitter tasting compounds in order to delay their release. This delayed release can permit the prior release of bitter masking agents. Suppression of bitter taste was accomplished by encapsulating a bitter taste stimulus in erodible stearic acid microspheres, and embedding these 5 µmeter diameter microspheres in pullulan films that contain sucralose and peppermint oil as masking agents, along with an encapsulated masking agent (sucralose). Psychophysical tests demonstrated that films which encapsulated both quinine and sucralose produced a significant and continuous sweet percept when compared to films without sucralose microspheres. Films with both quinine and sucralose microspheres also produced positive hedonic scores that did not differ from control films that contained only sucralose microspheres or only empty (blank) microspheres. The encapsulation of bitter taste stimuli in lipid microspheres, and embedding these microspheres in rapidly dissolving edible taste films that contain masking agents in both the film base and in microspheres, is a promising approach for diminishing the bitter taste of drugs and related compounds.

6-n-propylthiouracil taste disruption and TAS2R38 nontasting form in Parkinson's disease

BACKGROUND

The few studies that evaluated taste function in Parkinson's disease (PD) showed inconsistent results. The inherited ability to taste the bitter compound of 6-n-propylthiouracil has been considered to be a paradigm of general taste perception. 6-n-propylthiouracil taste perception is mediated by the TAS2R38 receptor, and reduced 6-n-propylthiouracil sensitivity has been associated with several diseases not typically related to taste function.

OBJECTIVES

We evaluated the 6-n-propylthiouracil taste perception and the TAS2R38 gene as genetic risk factors for the development of idiopathic PD in PD patients and healthy controls (HC).

METHODS

The 6-n-propylthiouracil taste perception was assessed by testing the responsiveness, and the ability to recognize, 6-n-propylthiouracil and sodium chloride. The participants were classified for 6-n-propylthiouracil taster status and genotyped for the TAS2R38 gene.

RESULTS

A significant increase in the frequency of participants classified as 6-n-propylthiouracil nontasters and a reduced ability to recognize bitter taste quality of 6-n-propylthiouracil were found in PD patients when compared with healthy controls. The results also showed that only 5% of PD patients had the homozygous genotype for the dominant tasting variant of TAS2R38, whereas most of them carried the recessive nontaster form and a high number had a rare variant.

CONCLUSIONS

Our results show that 6-n-propylthiouracil taster status and TAS2R38 locus are associated with PD. The 6-n-propylthiouracil test may therefore represent a novel, simple way to identify increased vulnerability to PD. Moreover, the presence of the nontasting form of TAS2R38 in PD may further substantiate that disease-associated taste disruption may represent a risk factor associated with the disease. © 2018 International Parkinson and Movement Disorder Society.

Effect of chemical interaction between oleic acid and L-Arginine on oral perception, as a function of polymorphisms of CD36 and OBPIIa and genetic ability to taste 6-n-propylthiouracil

Oral sensitivity to fats varies in individuals influencing nutritional status and health. Variations in oleic acid perception are associated with CD36 and odorant binding protein (OBPIIa) polymorphisms, and 6-n-propylthiouracil (PROP) sensitivity, which is mediated by TAS2R38 receptor. L-Arginine (L-Arg) supplementation was shown to modify the perception of the five taste qualities. Here we analyzed the effect of three concentrations (5, 10, 15 mmol/L) of L-Arg on oral perception of oleic acid in forty-six subjects classified for PROP taster status and genotyped for TAS2R38, CD36 and OBPIIa polymorphisms. L-Arg supplementation was effective in increasing the perceived intensity of oleic acid in most subjects. The lowest concentration was the most effective, especially in PROP non-tasters or medium tasters, and in subjects with at least an allele A in CD36 and OBPIIa loci. Density Functional Theory (DFT) calculations were exploited to characterize the chemical interaction between L-Arg and oleic acid, showing that a stable 1:1 oleate·ArgH⁺ adduct can be formed, stabilized by a pair of hydrogen bonds. Results indicate that L-Arg, acting as a ‘carrier’ of fatty acids in saliva, can selectively modify taste response, and suggest that it may to be used in personalized dietetic strategies to optimize eating behaviors and health.

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

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

Taste assessment in normal weight and overweight individuals with co-occurring Binge Eating Disorder

BACKGROUND

Taste perception influences food choice, and may contribute to both weight status and disordered eating. Relatively little work has attempted to disentangle contributions of weight status and Binge Eating Disorder (BED) to human taste perception. We predicted weight status and BED would interact, showing difference in taste perception from non-eating disorder matched groups.

METHODS

The four study groups included: normal weight BED (NW BED), normal weight healthy controls (NW HC), overweight BED (OW BED), and overweight healthy controls (OW HC) (N = 60). Groups were matched for age (±5 years), ethnicity, and weight status. Participants were assessed using the Structured Clinical Interview for DSM-IV Axis I Disorders, the Eating Disorder Examination Version 16.0, and the NIH Toolbox Gustatory Assessment with additional taste solutions and taste stimulus delivered with edible taste strips.

RESULTS

Interactions were found between weight status and diagnosis on measures of regional taste intensity for quinine hydrochloride (CI 95% [44.61, 56.31], p = 0.018), sucrose (CI 95% [46.79, 56.45], p = 0.003), and 6-n-propylthiouracil (CI 95% [25.557, 39.269], p = 0.015). OW BED participants perceived these taste stimuli significantly less intensely than OW HC and NW BED. Whole mouth taste intensity tests at suprathreshold amounts did not reveal group differences. All four groups reported similar hedonic response to taste stimuli. Edible taste strips had medium to large significant correlations with NIH Gustatory Assessment taste stimuli.

CONCLUSIONS

There were significant differences in the taste perception of OW BED relative to the other three groups. These findings may provide partial explanation as to why previous studies correlating taste and weight status have mixed results. Replication in larger samples assessed longitudinally is needed to extend this work.

First objective evaluation of taste sensitivity to 6-n-propylthiouracil (PROP), a paradigm gustatory stimulus in humans

Practical and reliable methods for the objective measure of taste function are critically important for studying eating behavior and taste function impairment. Here, we present direct measures of human gustatory response to a prototypical bitter compound, 6-n-propyltiouracil (PROP), obtained by electrophysiological recordings from the tongue of subjects who were classified for taster status and genotyped for the specific receptor gene (TAS2R38), and in which taste papilla density was determined. PROP stimulation evoked negative slow potentials that represent the summated depolarization of taste cells. Depolarization amplitude and rate were correlated with papilla density and perceived bitterness, and associated with taster status and TAS2R38. Our study provides a robust and generalizable research tool for the quantitative measure of peripheral taste function, which can greatly help to resolve controversial outcomes on the PROP phenotype role in taste perception and food preferences, and be potentially useful for evaluating nutritional status and health.

Orosensory contributions to dysphagia: a link between perception of sweet and sour taste and pharyngeal delay time

Pharyngeal delay is a significant swallowing disorder often resulting in aspiration. It is suspected that pharyngeal delay originates from sensory impairment, but a direct demonstration of a link between oral sensation and pharyngeal delay is lacking. In this study involving six patients with complaints of dysphagia, taste sensation of the oral tongue was measured and subsequently related to swallowing kinematics. It was found that a response bias for sour taste was significantly correlated with pharyngeal delay time on paste, highlighting oral sensory contributions to swallow motor dysfunctions. Investigating the precise nature of such a link between oral sensation and dysphagia would constitute a basis for understanding the disorder. The results of this study highlight oral sensory contributions to pharyngeal swallow events and provide impetus to examine this link in larger samples of dysphagic patients.

Taste genetics and gastrointestinal symptoms experienced in chronic kidney disease

BACKGROUND/OBJECTIVES

It is unknown what causes uraemic symptoms in renal disease. Chronic kidney disease (CKD) patients are known to have increased levels of urea, sodium, potassium and phosphate in their saliva compared with those without renal disease. The present cross-sectional study investigated associations between known genetic traits of taste and self-reported upper gastrointestinal (GI) symptoms experienced in CKD patients with the changes in saliva composition found in renal failure.

SUBJECTS/METHODS

Fifty-six CKD patients (35 males, 21 females, age 67±14 years), with stages 4 and 5 renal failure, selected from a tertiary hospital renal outpatient clinic participated in this study. Subjects answered a questionnaire to assess upper GI symptoms and tested for the genetic taste recognition thresholds of thiourea, phenylthiocarbamide and sodium benzoate. Saliva samples were collected to determine biochemical composition. Possible associations between genetic taste variations, saliva composition and upper GI symptoms were investigated.

RESULTS

Of the 56 patients enroled, 29 (52%) reported major upper GI uraemic symptoms, whereas 27 (48%) had no symptoms or only minor complaints of dry mouth. There was a strong association between the symptomatic burden a patient experienced and the genetic ability to taste thiourea (P<0.0003). Uraemic symptoms of taste changes (P<0.004) and nausea (P<0.002) were found to be related to a patient's genetic ability to taste thiourea.

CONCLUSIONS

This study provides evidence that the genetic ability to taste thiourea as bitter, in combination with the increase in active compounds found in CKD patient's saliva, impacts on the uraemic upper GI symptoms experienced.

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.

Pharmacogenetics of taste: turning bitter pills sweet?

Poor palatability of oral drug formulations used for young children negatively influences medication intake, resulting in suboptimal treatment. Some children are more sensitive to bitter tastes than others. Bitter tasting status is currently assessed by phenotyping with 6-n-propylthiouracil (PROP) as a bitter probe. Recent studies showed that interindividual differences in PROP sensitivity can be largely explained by three SNPs in TAS2R38, encoding a bitter taste receptor. Gustin, involved in the development of taste buds, and the sweet receptor genotype potentially explain remaining parts of PROP sensitivity variability. Other TAS2 receptor bitter receptor genes may also play a role in bitter aversions. Dependent on their genotype, children may have different medication formulation preferences. Taste genetics could improve drug acceptance by enabling better-informed choices on adapting oral formulations to children’s taste preferences. This paper presents an overview of recent findings concerning bitter taste genetics and discusses these in the context of pediatric drug formulation.

A preference test for sweet taste that uses edible strips

A novel delivery method is described for the rapid determination of taste preferences for sweet taste in humans. This forced-choice paired comparison approach incorporates the non-caloric sweetener sucralose into a set of one-inch square edible strips for the rapid determination of sweet taste preferences. When compared to aqueous sucrose solutions, significantly lower amounts of sucralose were required to identify the preference for sweet taste. The validity of this approach was determined by comparing sweet taste preferences obtained with five different sucralose-containing edible strips to a set of five intensity-matched sucrose solutions. When compared to the solution test, edible strips required approximately the same number of steps to identify the preferred amount of sweet taste stimulus. Both approaches yielded similar distribution patterns for the preferred amount of sweet taste stimulus. In addition, taste intensity values for the preferred amount of sucralose in strips were similar to that of sucrose in solution. The hedonic values for the preferred amount of sucralose were lower than for sucrose, but the taste quality of the preferred sucralose strip was described as sweet. When taste intensity values between sucralose strips and sucralose solutions containing identical amounts of taste stimulus were compared, sucralose strips produced a greater taste intensity and more positive hedonic response. A preference test that uses edible strips for stimulus delivery should be useful for identifying preferences for sweet taste in young children, and in clinical populations. This test should also be useful for identifying sweet taste preferences outside of the lab or clinic. Finally, edible strips should be useful for developing preference tests for other primary taste stimuli and for taste mixtures.