Astringency is a trigeminal sensation that involves the activation of G protein-coupled signaling by phenolic compounds.

Astringency is an everyday sensory experience best described as a dry mouthfeel typically elicited by phenol-rich alimentary products like tea and wine. The neural correlates and cellular mechanisms of astringency perception are still not well understood. We explored taste and astringency perception in human subjects to study the contribution of the taste as well as of the trigeminal sensory system to astringency perception. Subjects with either a lesion or lidocaine anesthesia of the Chorda tympani taste nerve showed no impairment of astringency perception. Only anesthesia of both the lingual taste and trigeminal innervation by inferior alveolar nerve block led to a loss of astringency perception. In an in vitro model of trigeminal ganglion neurons of mice, we studied the cellular mechanisms of astringency perception. Primary mouse trigeminal ganglion neurons showed robust responses to 8 out of 19 monomeric phenolic astringent compounds and 8 polymeric red wine polyphenols in Ca(2+) imaging experiments. The activating substances shared one or several galloyl moieties, whereas substances lacking the moiety did not or only weakly stimulate responses. The responses depended on Ca(2+) influx and voltage-gated Ca(2+) channels, but not on transient receptor potential channels. Responses to the phenolic compound epigallocatechin gallate as well as to a polymeric red wine polyphenol were inhibited by the Gαs inactivator suramin, the adenylate cyclase inhibitor SQ, and the cyclic nucleotide-gated channel inhibitor l-cis-diltiazem and displayed sensitivity to blockers of Ca(2+)-activated Cl(-) channels.

Quantitation of resveratrol in red wines by means of stable isotope dilution analysis-ultra-performance liquid chromatography-Quan-time-of-flight mass spectrometry and cross validation.

A stable isotope dilution analysis (SIDA) was developed for the quantitative analysis of the health-promoting phytoalexin (E)-resveratrol in red wines by means of UPLC-QuanTOF-MS. After hemisynthetic preparation of (E)-3,5,4'-trihydroxy-2,4,6-trideuterostilbene ((E)-[(2)H(3)]-resveratrol) as the stable isotope labeled internal standard, validation experiments revealed recovery rate of 96.2 ± 0.8% RSD, thus demonstrating the robustness and accuracy of the SIDA-UPLC-QuanTOF-MS method. Repeatability and reproducibility expressed as RSD showed excellent values of 3.0% and 4.0% for (E)-[(2)H(3)]-resveratrol. Cross validation against a SIDA-HPLC-MS/MS analysis using a triple quadrupole mass spectrometer revealed comparable data, but the SIDA-UPLC-QuanTOF-MS was four times faster, thus making the latter method preferential for an accurate high-throughput analysis of wine samples. Comparison of the SIDA data to those obtained by quantitation using a standard addition method and external calibration, respectively, revealed 97.7% and 32.4% of the resveratrol concentration determined by means of SIDA-UPLC-QuanTOF-MS and 101.0% and 12.7% of the resveratrol levels found by using SIDA-HPLC-MS/MS.

Compositional and sensory characterization of red wine polymers.

After isolation from red wine by means of ultrafiltration and gel adsorption chromatography, the composition of the highly astringent tasting high-molecular weight polymers was analyzed by means of HPLC-MS/MS, HPLC-UV/vis, and ion chromatography after thiolytic, alkaline, and acidic depolymerization and, on the basis of the quantitative data obtained as well as model incubation experiments, key structural features of the red wine polymers were proposed. The structural backbone of the polymers seems to be comprised of a procyanidin chain with (-)-epicatechin, (+)-catechin, (-)-epicatechin-3-O-gallate units as extension and terminal units as well as (-)-epigallocatechin as extension units. In addition, acetaldehyde was shown to link different procyanidins at the A-ring via an 1,1-ethylene bridge and anthocyanins and pyranoanthocyanins were found to be linked to the procyanidin backbone via a C-C-linkage at position C(6) or C(8), respectively. Alkaline hydrolysis demonstrated the polymeric procyanidins to be esterified with various organic acids and phenolic acids, respectively. In addition, the major part of the polysaccharides present in the red wine polymeric fraction were found not to be covalently linked to procyanidins. Interestingly, sensory evaluation of individual fractions of the red wine polymers did not show any significant difference in the astringent threshold concentrations, nor in the astringency intensity in supra-threshold concentrations and demonstrated the mean degree of polymerization as well as the galloylation degree not to have an significant influence on the astringency perception.

Reconstitution of the flavor signature of Dornfelder red wine on the basis of the natural concentrations of its key aroma and taste compounds.

By application of aroma extract dilution analysis (AEDA) on the volatile fraction isolated from a Dornfelder red wine, 31 odor-active compounds were identified by means of HRGC-MS and comparison with reference compounds. A total of 27 odorants, judged with high FD factors by means of AEDA, was quantitated by means of stable isotope dilution assays, and acetaldehyde was determined enzymatically. In addition, 36 taste-active compounds were analyzed by means of HPLC-UV, HPLC-MS/MS, and ion chromatography. The quantitative data obtained for the identified aroma and taste compounds enabled for the first time the reconstruction of the overall flavor of the red wine. Sensory evaluation of both the aroma and taste profiles of the authentic red wine and the recombinate revealed that Dornfelder red wine was closely mimicked. Moreover, it was demonstrated that the high molecular weight fraction of red wine is essential for its astringent taste impression. By comparison of the overall odor of the aroma recombinate in ethanol with that of the total flavor recombinate containing all tastants, it was shown for the first time that the nonvolatile tastants had a strong influence on the intensity of certain aroma qualities.

Matrix-calibrated LC-MS/MS quantitation and sensory evaluation of oak Ellagitannins and their transformation products in red wines.

Aimed at investigating the concentrations and taste contribution of the oak-derived ellagitannins castalagin and vescalagin as well as their transformation products acutissimin A/B, epiacutissimin A/B, and beta-1-O-ethylvescalagin in red wine, a highly sensitive and accurate quantification method was developed on the basis of LC-MS/MS-MRM analysis with matrix calibration. Method validation showed good recovery rates ranging from 102.4 +/- 5.9% (vescalagin) to 113.7 +/- 15.2% (epiacutissimin A). In oak-matured wines, castalagin was found as the predominant ellagitannin, followed by beta-1-O-ethylvescalagin, whereas the flavano-C-ellagitannins (epi)acutissimin A/B were present in significantly lower amounts. In contrast to the high threshold concentration levels (600-1000 micromol/L) and the puckering astringent orosensation induced by flavan-3-ols, all of the ellagitannin derivatives were found to induce a smooth and velvety astringent oral sensation at rather low threshold concentrations ranging from 0.9 to 2.8 micromol/L. Dose/activity considerations demonstrated that, among all the ellagitannins investigated, castalagin exclusively exceeded its threshold concentration in various oak-matured wine samples.