The role of TRPA1 and TRPV1 in the perception of astringency.

Astringency, commonly described as a drying, roughening, and/or puckering sensation associated with polyphenol-rich foods affects their palatability. While the compounds eliciting astringency are known, its mechanism of action is debated. This study investigated the role of transient receptor potential (TRP) channels A1 and V1 in astringency perception. If TRP A1 or V1 have a functional role in astringency perception, then desensitizing these receptors should decrease perceived astringency. Thirty-seven panelists underwent unilateral lingual desensitization of TRP A1 and V1 channels using mustard oil and capsaicin, respectively. Panelists then evaluated four astringent stimuli: epicatechin (EC), epigallocatechin gallate (EGCG), tannic acid (TA), and potassium alum (Alum), via 2-AFC and intensity ratings. When TRPA1 receptors were desensitized on one half of the tongue via mustard oil, no significant differences were observed between the treated and untreated sides for both 2-AFC and intensity ratings. Similarly, when TRPV1 receptors were desensitized on one half of the tongue via capsaicin, no significant differences were observed between the treated and untreated sides for both 2-AFC and intensity ratings. These findings challenge the notion that TRP channels play a pivotal role in astringency perception.

Kim MS ，Simons CT 《-》

Quantification of Oral Roughness Perception and Comparison with Mechanism of Astringency Perception.

Texture contributes to food acceptance, but oral texture perception is incompletely understood. Presently, we quantified individual sensitivities to lingual tactile roughness and assessed the impact of age, salivary flow (SF), and fungiform papillae density (FPD) on threshold and suprathreshold perception. Additionally, we tested the hypothesis that individuals highly sensitive to tactile roughness exhibit sensitivity to astringent stimuli. Detection thresholds (DTs) were determined using the staircase method for surface roughness from stainless steel coupons (Ra; 0.177-0.465 µm) and astringency elicited by epigallocatechin gallate (EGCG; 0-1.64 mM) and tannic acid (TA; 0-0.71 mM) from 30 individuals. Suprathreshold sensitivity was assessed from intensity ratings of electroforming comparator surfaces with roughnesses ranging from 0.51 to 22.8 µm and astringent stimuli ranging from 0 to 5.2 mM (EGCG) and from 0 to 1.9 mM (TA). SF, FPD, and astringent food pleasantness scores were collected. Variability in threshold roughness sensitivity enabled dividing subjects into high (RHi; n = 16) and low (RLo; n = 14) sensitivity groups; however, no significant differences in age, FPD, or SF were observed across these cohorts. Interestingly, compared with RLo, the RHi group exhibited greater sensitivity to EGCG but not TA astringency and indicated greater pleasantness from astringent foods (e.g., unripe bananas and dark chocolate). When participants were allocated into high (SalivaHi; n = 15) or low SF (SalivaLo; n = 15) groups, TA-evoked astringency thresholds were significantly lower in SalivaHi whom also indicated greater pleasantness from astringent red wines. For suprathreshold assessments of surface roughness or astringency, no significant associations were identified with age, FPD, or SF. Suprathreshold roughness sensitivity was, however, associated with suprathreshold sensitivity to EGCG but not TA astringency.

Linne B ，Simons CT 《-》

Auto-oxidation products of epigallocatechin gallate activate TRPA1 and TRPV1 in sensory neurons.

The sensation of astringency is elicited by catechins and their polymers in wine and tea. It has been considered that catechins in green tea are unstable and auto-oxidized to induce more astringent taste. Here, we examined how mammalian transient receptor potential V1 (TRPV1) and TRPA1, which are nociceptive sensors, are activated by green tea catechins during the auto-oxidation process. Neither TRPV1 nor TRPA1 could be activated by any of the freshly prepared catechin. When one of the major catechin, epigallocatechin gallate (EGCG), was preincubated for 3h in Hank's balanced salt solution, it significantly activated both TRP channels expressed in HEK293 cells. Even after incubation, other catechins showed much less effects. Results suggest that only oxidative products of EGCG activate both TRPV1 and TRPA1. Dorsal root ganglion (DRG) sensory neurons were also activated by the incubated EGCG through TRPV1 and TRPA1 channels. Liquid chromatography-mass spectrometry revealed that theasinensins A and D are formed during incubation of EGCG. We found that purified theasinensin A activates both TRPV1 and TRPA1, and that it stimulates DRG neurons through TRPV1 and TRPA1 channels. Results suggested a possibility that TRPV1 and TRPA1 channels are involved in the sense of astringent taste of green tea.

Kurogi M ，Kawai Y ，Nagatomo K ，Tateyama M ，Kubo Y ，Saitoh O ... -  《-》

Overexpression of artemin in the tongue increases expression of TRPV1 and TRPA1 in trigeminal afferents and causes oral sensitivity to capsaicin and mustard oil.

Elitt CM ，Malin SA ，Koerber HR ，Davis BM ，Albers KM ... -  《BRAIN RESEARCH》

Salivary protein levels as a predictor of perceived astringency in model systems and solid foods.

Salivary protein difference value (SP D-value) is a quantitative measure of salivary protein replenishment, which reportedly relates to individual differences in perceived astringency. This in vitro measure is calculated as the difference in total salivary protein before (S1) and after (S2) stimulation with tannic acid, with a greater absolute value (S2-S1) indicating less protein replenishment. Others report that this measure predicts perceived astringency and liking of liquid model systems and beverages containing added polyphenols. Whether this relationship generalizes to astringent compounds other than polyphenols, or to solid foods is unknown. Here, the associations between SP D-values and perceived astringency and overall liking/disliking for alum and tannic acid (experiment 1) as well as solid chocolate-flavored compound coating with added tannic acid or grape seed extract (GSE) (experiment 2) were examined. In both experiments, participants (n=84 and 81, respectively) indicated perceived intensity of astringency, bitterness, sweetness, and sourness, and degree of liking of either aqueous solutions, or solid chocolate-flavored compound coating with added astringents. Data were analyzed via linear regression, and as discrete groups for comparison to prior work. Three discrete groups were formed based on first and third quartile splits of the SP D-value distribution: low (LR), medium (MR), and high responding (HR) individuals. In experiment 1, significantly higher mean astringency ratings were observed for the HR as compared to the LR/MR groups for alum and tannic acid, confirming and extending prior work. In experiment 2, significantly higher mean astringency ratings were also observed for HR as compared to LR groups in solid chocolate-flavored compound containing added tannic acid or GSE. Significant differences in liking were found between HR and LR groups for alum and tannic acid in water, but no significant differences in liking were observed for chocolate-flavored compound samples. A significant linear relationship between SP D-values and perceived astringency was observed for both alum and tannic acid (p's<0.001), although the variance explained was relatively low (R(2)=0.33 and 0.29, respectively). In the solid chocolate-flavored compound spiked with either tannic acid or GSE, the relationship was not significant (p=0.17 and 0.30; R(2)=0.03 and 0.02, respectively). Due to the weak associations overall, and the lack of significant differences in perception of astringency between the MR and LR groups, we conclude that SP D-values are not a strong predictor of astringency, especially in solid, high-fat foods. Additional research investigating alternative methods for quantifying individual differences in astringency, as well as exploring the underlying complexities of this percept appears warranted.

Fleming EE ，Ziegler GR ，Hayes JE 《-》