Thermal Taste Research Articles

The control effect and mechanism of antioxidants on the flavor deterioration of Sichuan pepper essential oil during thermal processing

The impacts of varying heating temperature on the flavor of Sichuan pepper essential oil (SPEO) have been studied. The high temperature heating was found to accelerate the oxidation of SPEO and caused the deterioration of its flavor (odor and pungency taste). With the intervention of antioxidants including RE, AP, and TPP, both thermal oxidation stability and flavor stability of SPEO were enhanced. Addition of 1.5% TPP had the best control effect, which significantly improved the overall flavor of heated SPEO and made the overall flavor of SPEO heated at 100°C highly similar to that of original SPEO. According to the results of GC-MS and OAV analyses, the control effect of antioxidants on odor deterioration of SPEO was mainly through significantly inhibiting the decrease in content and OAV of both linalool and terpenes, and restricting the formation of some oxygenated compounds such as aldehydes. The results of HPLC analysis showed that the control effect of antioxidants on the thermal taste stability of SPEO was mainly dependent on blocking the chemical reactions of sanshools, especially hydroxy-α-sanshool.

On being a foodie: development of the Foodie Index and association with personality and taste phenotype

Although foodies represent an important and growing consumer segment, and the term itself is widely used in popular writings and social media, foodies are poorly described in the academic literature. Additionally, little is known regarding how ‘foodiness’ associates with personality and taste acuity, despite these dimensions being important components of consumers’ food preferences and intake. In this explorative study, we describe the development of a 12-item instrument – the Foodie Index (TFI) – comprising of four subscales: food enjoyment and interest, time investment, monetary investment, and knowledge. Overall, TFI and its subscales display good internal reliability (Cronbach’s alpha and mean interitem correlation). As hypothesised, TFI scores differ between individuals and associate positively with food adventurousness (p(r) < 0.001). Responses to TFI allowed participants to be categorised as foodies (n = 185) or non-foodies (n = 188), and we assessed whether personality measures (the Adult Impulsiveness, Venturesomeness and Empathy Scale and the Big Five Inventory) and taste acuity (the PROP Taster Status and Thermal Taster Status phenotypes) differ between these groups. Compared with non-foodies, foodies are more venturesome (p(t) = 0.05), extraverted (p(t) = 0.01) and open to experience (p(t) = 0.02). PROP responsiveness did not vary with TFI scores nor differ between foodies and non-foodies. In contrast, foodies were more likely to be thermal tasters (p(χ2) = 0.005) and scores on all four subscales of TFI were higher for thermal tasters than for thermal non-tasters (p(t) < 0.05). TFI will support further research into identifying the characteristics of foodies and provide opportunities for retailers and marketers of food-related products and services to segment and more fully understand their consumers.

Comparing a new rapid combined method (RapCoTT) with traditional approaches for phenotyping thermal taste

Thermal taste is the phenomenon whereby taste is induced in some individuals through the application of a changing temperature stimulus to the tongue. Research into thermal taste is currently limited by inefficient phenotyping methods, which result in large numbers of unclassified individuals. This study evaluated the performance of a new, rapid combined phenotyping approach (RapCoTT) compared to two classification approaches using traditional phenotyping methods. RapCoTT was found to be more efficient at classifying participants, whilst showing consistency in classification with existing approaches. However, learning effects impacted the efficiency of all methods, which are a likely consequence of the unusual nature of thermal taste. It was concluded that three training steps be included for the phenotyping, namely taste exposure, TCATA training and a practice run. RapCoTT was found to evoke similar patterns of perceived tastes to other methods, with some exceptions. RapCoTT provides a more efficient tool for categorising participants for comparing sensory perception and food choice behaviours within the Thermal taste phenotype and provides a robust approach for future research into the phenomenon of thermal taste.

Perception of Aqueous Ethanol Binary Mixtures Containing Alcohol-Relevant Taste and Chemesthetic Stimuli

Ethanol is a complex stimulus that elicits multiple gustatory and chemesthetic sensations. Alcoholic beverages also contain other tastants that impact flavour. Here, we sought to characterize the binary interactions between ethanol and four stimuli representing the dominant orosensations elicited in alcoholic beverages: fructose (sweet), quinine (bitter), tartaric acid (sour) and aluminium sulphate (astringent). Female participants were screened for thermal taste status to determine whether the heightened orosensory responsiveness of thermal tasters (n = 21–22) compared to thermal non-tasters (n = 13–15) extends to these binary mixtures. Participants rated the intensity of five orosensations in binary solutions of ethanol (5%, 13%, 23%) and a tastant (low, medium, high). For each tastant, 3-way ANOVAs determined which factors impacted orosensory ratings. Burning/tingling increased as ethanol concentration increased in all four binary mixture types and was not impacted by the concentration of other stimuli. In contrast, bitterness increased with ethanol concentration, and decreased with increasing fructose concentration. Sourness tended to be reduced as ethanol concentration increased, although astringency intensity decreased with increasing concentration of fructose. Overall, thermal tasters tended to be more responsive than thermal non-tasters. These results provide insights into how the taste and chemesthetic profiles of alcoholic beverages across a wide range of ethanol concentrations can be manipulated by changing their composition.

Thermal taster status: Temperature modulation of cortical response to sweetness perception

Temperature is known to impact taste perception, but its reported effect on sweet taste perception in humans is inconsistent. Here, we assess whether thermal taste phenotype alters the temperature modulation of the brains’ response to sweet samples and sweet taste perception. Participants (n = 24 balanced for thermal tasters (TT) and thermal non-tasters (TnT), 25 ± 7 years (mean ± SD), 10 males) underwent a thermal taste phenotyping session to study responses to cooling and warming of the tongue using a thermode. In a separate session, functional Magnetic Resonance Images (fMRI) were collected during sweet samples (87 mM sucrose) delivery at two temperatures (‘cold’ (5 ± 2 °C) and ‘ambient’ (20 ± 2 °C)) and the perceived sweetness intensity rated.In the phenotyping session, TTs had heightened perceptual temperature sensitivity to cooling and warming of the tongue using a thermode compared to TnTs. Although there was no significant effect during the fMRI session, the fMRI response to the ‘cold sweet’ sample across all participants was significantly increased in anterior insula/frontal operculum and mid-insula compared to the ‘ambient sweet’ sample, likely to reflect the perceptual difference to temperature rather than taste perception. TTs showed significantly increased fMRI activation patterns compared with TnTs and an interaction effect between thermal taster status and sample temperature, with TTs showing selectively greater cortical responses to ‘cold sweet’ samples compared to TnTs in somatosensory regions (SI and SII).The increase in cortical activation in somatosensory cortices to the ‘cold sweet’ stimulus correlated with perceptual ratings of temperature sensitivity to the thermode. The results highlight the importance of investigating the effects of thermal taster phenotype across a range of temperatures representing the reality of consumer consumption to beverages.

Homogeneity of thermal tasters and implications for mechanisms and classification

Thermal tasting, an important type of individual variation in orosensation, is a phenomenon by which some individuals perceive thermally-induced taste sensations simply by having the tip of their tongue warmed or cooled. These individuals, known as thermal tasters, report a variety of thermally-elicited tastes (typically sweet, sour, salty, bitter, metallic) and the tastes reported can vary with the temperature regime used (warming or cooling) and location on the tongue tested. Importantly, when compared to thermal non-tasters, thermal tasters are more responsive to aqueous solutions of basic tastants and to beverages. The mechanism(s) underlying thermal tasting are not well understood and it is unknown if the increased orosensory responsiveness of thermal tasters is universal or if it is driven by a subgroup of thermal tasters. Thermal taste data from 12 previous studies was combined to obtain a large sample of thermal tasters (n = 254) who were divided into subgroups based on the type of thermally-elicited taste reported and the temperature regime/location at which it was experienced. Sweet thermal tasters (n = 77) were 9 times more likely than non-sweet thermal tasters (n = 177) to experience thermally-elicited sensations during lingual warming (p < 0.0001). Similarly, sour thermal tasters (n = 89) were 8 times more likely than non-sour thermal tasters (n = 165) to report thermally induced tastes during cooling (p<0.0001). However, no differences in orosensory responsiveness based on these or other subgroups were identified, suggesting that the heightened orosensory responsiveness of thermal tasters may be centrally-mediated. We discuss how these findings inform our understanding of the mechanism(s) underlying thermal taste and the identification of thermal taste subgroups, along with practical implications of methodological differences in determining thermal taste status.

Exploring the relationships between taste phenotypes, genotypes, ethnicity, gender and taste perception using Chi-square and regression tree analysis

It is well known that perceived taste intensity varies greatly among individuals, and that several factors including taste phenotypes (PROP Taster Status (PTS), Sweet Liking Status (SLS), Thermal Taster Status (TTS)), ethnicity and gender, contribute to variation in taste responsiveness, although such factors are usually investigated in isolation. This study aimed to investigate the association between different taste pheno/genotypes, explore whether these taste phenotypes associated with ethnicity (Caucasian vs Asian) and gender, and determine the relative effects of the different factors on perceived taste intensity. As analysis of this type of data with ANOVA can be difficult due to confounding factors, interactions, and small sample sizes in subcategories, the use of regression tree analysis as an alternative approach was investigated. To that end, two-hundred and twenty-three volunteers were phenotyped for their PTS, SLS and TTS and genotyped for TAS2R38 –rs713598 and gustin –rs2274333. They also rated their perceived intensity of five basic taste and metallic solutions on a gLMS scale. No significant association between the three taste phenotypes were found indicating PTS, SLS and TTS are independent taste phenotypes. However, the results indicated that Asians were not only more likely to be PROP supertasters, but also more likely to be thermal tasters or Low Sweet Likers, compared to Caucasians. Gender was also significantly associated with SLS, where males were more likely to be High Sweet Likers. For perceived taste intensity, traditional ANOVA analysis proved to be challenging. The alternative approach, using regression trees, was shown to be an effective tool to provide a visualised framework to demonstrate the multiple interactions in this dataset. For example, ethnicity was the most influencing factor for perceived sour and metallic taste intensity, where Asians had heightened response compared to Caucasians. The regression tree analysis also highlighted that the PTS effect was dependent on ethnicity for sour taste, and PTS and TTS effect was dependent on ethnicity for metallic taste. This study is the first study to use regression tree analysis to explore variation in taste intensity ratings, and demonstrated it can be an effective tool to handle and interpret complex sensory datasets.

Sweet Thermal Taste: Perceptual Characteristics in Water and Dependence on TAS1R2/TAS1R3.

The initial objective of this study was to determine if activation of the sweet taste receptor TAS1R2/TAS1R3 is necessary for perception of sweet thermal taste (swTT). Our approach was to inhibit the receptor with the inverse agonist lactisole using a temperature-controlled flow gustometer. Because all prior studies of thermal taste (TT) used metal thermodes to heat the tongue tip, we first investigated whether it could be generated in heated water. Experiment 1 showed that sweetness could be evoked when deionized water was heated from 20 to 35 °C, and testing with static temperatures between 20 and 35 °C demonstrated the importance of heating from a cool temperature. As in previous studies, thermal sweetness was reported by only a subset of participants, and replicate measurements found variability in reports of sweetness across trials and between sessions. Experiment 2 then showed that exposure to 8 mM lactisole blocked perception of swTT. Confirmation of the involvement of TAS1R2/TAS1R3 led to an investigation of possible sensory and cognitive interactions between thermal and chemical sweetness. Using sucrose as a sweet stimulus and quinine as a nonsweet control, we found that dynamic heating capable of producing thermal sweetness did not increase the sweetness of sucrose compared with static heating at 35 °C. However, swTT was disrupted if trials containing sucrose (but not quinine) were interspersed among heating-only trials. These findings provide new information relevant to understanding the perceptual processes and receptor mechanisms of swTT, as well as the heat sensitivity of sweet taste in general.

Variation in Orosensory Responsiveness to Alcoholic Beverages and Their Constituents—the Role of the Thermal Taste Phenotype

Orosensory perception strongly influences food and beverage liking and consumption. Differences between individuals in orosensation present an opportunity to conceptualize and commercialize products based on consumer “taste” responsiveness. The main objective of this study was to examine how the thermal taste phenotype associates with orosensory responsiveness to beer and cider, and more generally to examine differences in and relationships between responsiveness to alcohol-relevant stimuli and to beer/cider. Sixty participants (31 thermal tasters (TTs) and 29 thermal non-tasters (TnTs)) rated the intensity of aqueous solutions of beer- and cider-relevant tastants: iso-α-acid (bitterness), ethanol (irritation, bitterness, sweetness), dextrose (sweetness), and citric acid (sourness) at concentrations typically found in commercial products on generalized labeled magnitude scales (gLMS). Intensity ratings (gLMS) of multiple orosensations elicited by six beer and two cider samples differing in iso-α-acid and ethanol content were also collected. TTs scored the bitterness of ethanol more intensely than did TnTs (p(t) < 0.05) and rated the bitterness, sourness, astringency, and overall taste intensity of sampled beers and ciders higher than TnT (p(F) < 0.05). Thermal taste status is an important determinant in the perception of beer and cider flavor. These results may assist product developers in designing beers and ciders targeted to specific consumer segments that differ in orosensory responsiveness, and inform broader understanding of the sources of variation in human perception of alcohol constituents and beverages.

Examination and Validation of Classification Schema for Determining Thermal Taste Status

Thermal taster status (TTS) is determined when the tongue is cooled or warmed, whereby thermal tasters (TT) experience a taste sensation while thermal nontasters (TnT) do not. The literature suggests that TT experience greater responsiveness (higher intensity ratings) to orosensory stimuli; however, small sample sizes and differences in classification schemes between studies confound our understanding of TTS. In addition, up to 50% of individuals (nonclassifiables, NC) have been excluded from previous studies and have yet to be characterized. Raw responses to the thermal-elicitation procedure were used to determine the TTS of the same participants using four published classification schemes, and concordance between the schemes was examined using Fleiss’ kappa. Using a large convenience sample (n = 708), we tested for differences in orosensory (ANOVA) and temperature (Mann-Whitney U) responsiveness between TT, TnT, and NC. TT are more responsive than TnT to both orosensations and temperature changes, regardless of the classification method used despite only moderate concordance between the schemes. Overall, the orosensory and temperature responsiveness of NC is intermediate to that of TT and TnT. However, the responses of NC are not homogeneous and subgroups are identified. The trend of TT being more responsive to orosensory and temperature stimuli is confirmed. The responsiveness patterns of NC subgroups suggest they are misclassified TT and TnT, and can be included in future studies examining thermal tasting. TTS is an important source of individual differences in orosensory responsiveness, and our findings inform best practices for thermal elicitation and classification.

Application of TCATA to examine variation in beer perception due to thermal taste status

Thermal taste status (TTS) describes a phenotype whereby some individuals experience a thermally-induced taste on thermal stimulation of the tongue (thermal tasters; TTs) and some do not (thermal non-tasters; TnTs). TTs experience a range of orosensations elicited by aqueous solutions and some beverages more intensely than TnTs. Whether this extends throughout ingestion duration is unknown, despite the fact that the evolution of flavour on the palate is a key component of consumer acceptance of food/beverages. We sought to use temporal-check-all-that-apply (TCATA) to determine how beer perception varies with TTS. A secondary aim was to investigate the effects of serving temperature and a concurrent auditory cue on TCATA responses and how these may interact with TTS. Forty-one female participants (21 TTs, 20 TnTs) were trained to identify seven dominant sensations elicited by a de-alcoholized beer (astringent, bitter, carbonation, fruity/hops, malty, sour, sweet). Beer samples were served in duplicate at either 6 °C or 21 °C with or without a concurrent auditory cue consisting of a sound clip of effervescence. TTs cited astringent and bitter more frequently than TnTs (p(F) ≤ 0.01), and the area under the curve (AUC) was greater for TTs for several sensations (p(t) < 0.05). Samples served at 6 °C had higher carbonation citation frequencies (p(F) < 0.001) and AUC at 0–30 s (p(t) < 0.001) and 30.1–60 s (p(t) < 0.05) than the warmer samples, with responses for astringent following a same pattern. AUC for carbonation and astringent varied within the sound conditions at 0–30 s (p(t) < 0.05). Overall, these results show that the ‘taste’ advantage of TTs extends to beer, and that temporal methods are needed to more fully describe consumer variation.

New Thermal Taste Actuation Technology for Future Multisensory Virtual Reality and Internet.

Today's virtual reality (VR) applications such as gaming, multisensory entertainment, remote dining, and online shopping are mainly based on audio, visual, and touch interactions between humans and virtual worlds. Integrating the sense of taste into VR is difficult since humans are dependent on chemical-based taste delivery systems. This paper presents the 'Thermal Taste Machine', a new digital taste actuation technology that can effectively produce and modify thermal taste sensations on the tongue. It modifies the temperature of the surface of the tongue within a short period of time (from 25°C to 40 °C while heating, and from 25°C to 10 °C while cooling). We tested this device on human subjects and described the experience of thermal taste using 20 known (taste and non-taste) sensations. Our results suggested that rapidly heating the tongue produces sweetness, fatty/oiliness, electric taste, warmness, and reduces the sensibility for metallic taste. Similarly, cooling the tongue produced mint taste, pleasantness, and coldness. By conducting another user study on the perceived sweetness of sucrose solutions after the thermal stimulation, we found that heating the tongue significantly enhances the intensity of sweetness for both thermal tasters and non-thermal tasters. Also, we found that faster temperature rises on the tongue produce more intense sweet sensations for thermal tasters. This technology will be useful in two ways: First, it can produce taste sensations without using chemicals for the individuals who are sensitive to thermal taste. Second, the temperature rise of the device can be used as a way to enhance the intensity of sweetness. We believe that this technology can be used to digitally produce and enhance taste sensations in future virtual reality applications. The key novelties of this paper are as follows: 1. Development of a thermal taste actuation technology for stimulating the human taste receptors, 2. Characterization of the thermal taste produced by the device using taste-related sensations and non-taste related sensations, 3. Research on enhancing the intensity for sucrose solutions using thermal stimulation, 4. Research on how different speeds of heating affect the intensity of sweetness produced by thermal stimulation.

The impact of PROP and thermal taster status on the emotional response to beer

With an increasingly competitive global market, understanding consumer emotional response to products can provide a different perspective to identify drivers of consumer food choice behaviour beyond traditional hedonic measurement. This study investigated how two taste phenotypes (Thermal taster status (TTS) and PROP taster status (PTS)) impacted liking and emotional response to beers varying in bitterness, carbonation and serving temperature. Volunteers (n = 60, balanced for TTS and PTS) were invited to express their liking and emotional response to 2 commercial beers of contrasting bitterness, presented at two different carbonation levels (commercial carbonation and low carbonation level) and served at two temperatures (cold and ambient). In general, when beers were served at their commercial carbonation level and at a cold temperature, they received higher liking scores and evoked more positive emotions and less negative emotions. Signficant temperature ∗ carbonation interactions were found for liking and some emotion categories. At commercial carbonation levels, cold beer was better liked and evoked more positive emotions than beer served at ambient temperature, but no such temperature effect was observed at the low carbonation level. Although the sample size was relatively small, significant effects for liking were observed for PTS but not TTS, suggesting PTS is a more influential factor regarding liking than TTS. However, thermal tasters (TT) rated 6 out of 10 emotion categories significantly higher for beer than thermal non-tasters (TnT), indicating emotional response may be more sensitive to capture the differences across taste phenotypes than liking, and that TT show increased negative emotions to beer in general. PROP supertasters (ST) rated some emotion categories significantly higher than non-tasters (NT) and, in contrast to TTS these were the more positive emotions, such as excited and content. This is the first study to report an impact of both TTS and PTS on emotional response. Furthermore, this study observed significant relative effects of TTS and PTS on emotional response, where the effect of PTS was more pronounced in TnT. This highlights the importance of investigating the combined effects of different phenotypes on consumer response representing the reality of different consumer segments.

Variation in thermally induced taste response across thermal tasters

Thermal tasters (TTs) perceive thermally induced taste (thermal taste) sensations when the tongue is stimulated with temperature in the absence of gustatory stimuli, while thermal non tasters (TnTs) only perceive temperature. This is the first study to explore detailed differences in thermal taste responses across TTs. Using thermal taster status phenotyping, 37 TTs were recruited, and the temporal characteristics of thermal taste responses collected during repeat exposure to temperature stimulation. Phenotyping found sweet most frequently reported during warming stimulation, and bitter and sour when cooling, but a range of other sensations were stated. The taste quality, intensity, and number of tastes reported greatly varied. Furthermore, the temperature range when thermal taste was perceived differed across TTs and taste qualities, with some TTs perceiving a taste for a small temperature range, and others the whole trial. The onset of thermal sweet taste ranged between 22 and 38°C during temperature increase. This supports the hypothesis that TRPM5 may be involved in thermal sweet taste perception as TRPM5 is temperature activated between 15 and 35°C, and involved in sweet taste transduction. These findings also raised questions concerning the phenotyping protocol and classification currently used, thus indicating the need to review practices for future testing. This study has highlighted the hitherto unknown variation that exists in thermal taste response across TTs, provides some insights into possible mechanisms, and importantly emphasises the need for more research into this sensory phenomenon.

Variation in orosensation and liking of sampled foods with thermal tasting phenotype

Flavour is a key driver of liking, purchase behaviour and consumption of food and beverages. Determining how individuals differ in their perception of flavour is important to fully understanding dietary choices and habitual diet-related health outcomes. Thermal tasting—the capacity to experience a phantom taste when small areas of the tongue are rapidly heated or cooled—associates with greater orosensory acuity for tastants in aqueous solutions. This study sought to extend this finding and establish whether thermal-taster status also associates with the perceived intensities of oral sensations elicited by sampled food. Twenty-five thermal tasters (TTs) and 19 thermal non-tasters (TnTs) scored liking (generalized degree of liking scale) and the intensity (generalized visual analogue scale) of the dominant orosensations elicited by 20 food and beverage items in duplicate using a randomized complete block design. Multiple analysis of variance (MANOVA) showed that overall, TTs rated the intensity of orosensory food groups higher than did TnTs, although this was significant only for foods that were predominantly bitter-eliciting (ANOVA). Overall liking scores approached significance (MANOVA) but differed between TTs and TnTs only for the grainy orosensory food grouping (ANOVA). These findings are discussed in the context of diet-related health outcomes and directions for further research concerned with taste phenotypes, flavour perception and consumption behaviours.

Does Liking and Orosensation Intensity Elicited by Sampled Foods Vary with Thermal Tasting?

Food choice and habitual diet-related health outcomes are strongly influenced by the oral sensations elicited by food. Of the biological-based mediators of orosensation, thermal tasting—the capacity to experience phantom taste sensations on lingual thermal stimulation—has not been investigated with respect to orosensation and liking of sampled foods. Twenty-three female thermal tasters (TTs) and 21 female thermal non-tasters (TnTs) scored liking of (9-point hedonic scale) and the intensity of orosensations elicited by (gVAS) 22 food and beverage items in duplicate using a randomized complete block design in a customized sensory evaluation laboratory. Foods selected included high fat, high sugar, and high salt items. Sampled items were grouped according to the dominant orosensation(s) elicited (sweet, bitter, sour, salty, astringent, creamy, crunchy, crispy, firm, menthol cool, and grainy), and intensity and liking assessed for each group. No significant differences were found for thermal tasting status (TTS) in intensity ratings of orosensory groupings (p(t) > 0.05). TnTs gave higher liking ratings for creamy foods than TTs (t = 5.99, p = 0.015), and their liking of the “aversive” food grouping was higher than for TTs and approached significance (t = 2.97, p = 0.086). The previously reported variation in orosensation due to TTS observed with simple aqueous solutions, and some beverages may not extend to sampled foods. However, differences in liking are suggested for some food groupings and are worthy of further investigation.

Thermal Tasting and Difference Thresholds for Prototypical Tastes in Wine

Thermal tasting—the capacity to experience phantom taste sensations on thermal stimulation of the tongue—has been shown to associate with greater responsiveness to orosensations elicited in aqueous solutions and beverages. Here, we sought to determine if this heightened acuity extends to difference thresholds. An ascending two-alternative forced choice method was used to measure difference thresholds for sweetness (sucrose), sourness (tartaric acid), and bitterness (quinine) in a neutral white wine. Individual best-estimate thresholds (BETs) were calculated according to ASTM E-679-04. Group difference thresholds (g/L) for thermal tasters (TT) and thermal non-tasters (TnT), respectively, were sweetness, 3.52 and 5.24; sourness, 0.23 and 0.70; and bitterness, 0.0058 and 0.0060. There was an overall trend of TTs having lower difference thresholds than TnTs, but this was significant only for sourness (t = 3.95, p = 0.002). Additionally, wine expertise was inversely associated with the difference threshold for sweetness (rho = −0.470, p = 0.029) and was a significant source of variation in the analysis of covariance (t = −2.69, t = 0.016). These data provide some preliminary evidence that the supra-threshold intensity “advantage” in orosensory perception previously reported for thermal tasters may extend to difference thresholds and complex products such as wine. These results add to the evidence that thermal tasting represents a potentially important taste phenotype that may associate with food preference and consumption and should also be considered when populating sensory panels.

Phenotypic variation in oronasal perception and the relative effects of PROP and Thermal Taster Status

Individual variation in taste perception has long been investigated, particular in relation to PROP taster status (PTS). Recently, a new marker has been identified, Thermal Taster Status (TTS), whereby individuals are categorised as thermal tasters (TTs) or thermal non-tasters (TnTs) based on their ability to perceive taste solely from temperature stimulation. The aim of this study was to investigate the incidence of thermal tasters and relative effects of PTS and TTS on oronasal sensitivity across the whole perceptual range. Both detection thresholds (ASTM E679) and intensity measures at suprathreshold level (rated on gLMS) for stimuli from a range of modalities were determined from up to 124 subjects pre-screened for their PTS and TTS. For the detection threshold tests stimuli included tastants (sucrose, NaCl, caffeine), trigeminal stimuli (N-ethyl-2-isopropyl-5-methylcyclohexanecarboxamide (WS3) and capsaicin), and aromas (ethyl butyrate and isoamyl acetate). Tastants (sucrose, NaCl, citric acid and caffeine) plus capsaicin as a trigeminal stimulus were evaluated at suprathreshold level. No significant differences were found within either PTS or TTS groups at detection threshold level, with one exception; TTs had a lower threshold for sucrose (p<0.05). At supra-threshold level, PROP supertasters (pSTs) and medium tasters (pMTs) rated stimuli higher than non-tasters, and a consistent trend was observed that TTs rated stimuli higher than TnTs, although only ratings for temperature (warm and cold) reached significance. Global analyses applied across each modality, showed that in general TTs rated gustatory and trigeminal modalities significantly higher than TnTs, whilst this was not the case for olfactory stimuli, indicating that the mechanism for increased perception for TTs may be located in the oral cavity. PTS and TTS were shown to be independent phenotypes, but interestingly, ANOVA revealed significant interactions between TTS and PTS across the three modalities. Most notably, within pMTs, TTs rated stimuli intensity higher than TnTs, while the opposite trend was observed for pSTs. The intensity advantage gained by thermal tasters appears to be more apparent for pMTs than the already highly sensitive pSTs.

TAS2R38 Single Nucleotide Polymorphisms Are Associated with PROP—but Not Thermal—Tasting: a Pilot Study

T2R38 is a bitter taste receptor known to be associated with 6-n-propylthiouracil (PROP) responsiveness, as operationalized by PROP taster status (PTS). Suprathreshold PROP responsiveness is a proxy for general taste responsiveness and has been linked to diet-related behavior and health outcomes, including alcohol consumption, body mass index, and cardiovascular disease risk. The ability to taste PROP allows classification of individuals into three groups: super-tasters (pST), medium-tasters (pMT), or non-tasters (pNT). Recently, another taste phenotype, thermal tasting, has been identified, in which the heating or cooling of a region of one’s tongue evokes a phantom taste response in 20–50 % of individuals. The mechanism behind thermal tasting is not yet known. In this study, we sought to investigate the relationship between TAS2R38 sequence variation with both PROP responsiveness and thermal taster status (TTS). PTS was determined from participants’ intensity rating of a 3.2 mM PROP solution, while TTS was determined based on the presence/absence and intensity (generalized labeled magnitude scale) of oral sensation(s) elicited by temperature changes to a participant’s extended tongue applied by a computer-controlled thermode. Using buccal cell DNA, we performed genotyping of the TAS2R38 variations for 53 individuals, primarily of Caucasian decent. A significant correlation between PTS and three TAS2R38 single nucleotide polymorphisms (SNPs) (rs713598, rs1726866, and rs10246939) was found, as previously reported, with the strongest association seen when all three SNPs were included in the multiple regression model. However, not all PTS differences can be explained by variation at these three SNP sites or other sites in the coding region, suggesting the involvement of additional genes. Although in prior studies both PTS and TTS have been shown to predict general taste responsiveness, our data indicate no association between TTS and the TAS2R38 genotype, suggesting the involvement of different genes in this phenotype. While underpowered due to small sample size, our study was not able to confirm the previously reported association between Gustin SNP rs2274333 genotype and PROP responsiveness. This pilot study provides the first genetic evidence to support previous phenotype-based observation suggesting a lack of association between PROP responsiveness and thermal taster status. Specifically, our data show that TAS2R38 is unlikely to be involved in thermal tasting.

Influence of Stimulus Temperature on Orosensory Perception and Variation with Taste Phenotype

Recently, the phenomenon of thermal taste, where thermal tasters (TTs) perceive taste sensations from the application of thermal stimuli to the tongue, was described. Thermal taster status (TTS) appears to function as a marker of individual variation in orosensory perception, as TTs are more responsive to prototypical orosensory stimuli and flavor attributes in complex beverages than thermal non-tasters. The main objective of this study was to examine the influence of TTS on the relationship between stimulus temperature and orosensory perception. Propylthiouracil (PROP) responsiveness has long been used as an index of individual variation in oral sensation, as general orosensory responsiveness to a variety of stimuli associates with the ability and degree to which individuals perceive PROP's bitterness. PROP taster status (PTS), an expression of individuals' PROP responsiveness, was also examined. Perceptually equi-intense stimuli eliciting sweet, sour, bitter, and astringent sensations were presented at 5 °C and 35 °C and evaluated using time-intensity methodology. Unexpectedly, an apparent trend of TTs reporting higher maximum perceived intensities for all stimuli was not statistically significant, and an examination of individual subjects' data suggests further examination of the influence of TTS on orosensory stimuli is warranted. PROP bitterness and the perceived intensity of orosensory stimuli were not associated at either temperature; however, some differences between PTS groups were found. As previously reported, TTS and PTS interactions were not observed. Interestingly, temperature influenced the maximum intensity perceived from astringent, bitter, and sour stimuli, but not from the sweet stimulus.