Identification of the astringent taste compounds in black tea infusions by combining instrumental analysis and human bioresponse

Application of taste dilution analyses on freshly prepared black tea infusions revealed neither the high molecular weight thearubigen-like polyphenols nor the catechins and theaflavins, but a series of 14 flavon-3-ol glycosides as the main contributors to the astringent taste perceived upon black tea consumption. Among these glycosides, the apigenin-8-C-[alpha-L-rhamnopyranosyl-(1-->2)-O-beta-D-glucopyranoside] was identified for the first time in tea infusions. Depending on the structure, the flavon-3-ol glycosides were found to induce a velvety and mouth-coating sensation at very low threshold concentrations, which were far below those of catechins or theaflavins; for example, the threshold of 0.001 mumol/L found for quercetin-3-O-[alpha-L-rhamnopyranosyl-(1-->6)-O-beta-D-glucopyranoside] is 190,000, or 16,000 times below the threshold determined for epigallocatechin gallate or theaflavin, respectively. Moreover, structure/activity considerations revealed that, besides the type of flavon-3-ol aglycon, the type and the sequence of the individual monosaccharides in the glycosidic chain are key drivers for astringency perception of flavon-3-ol glycosides.