Evaluation of the taste contribution of theaflavins in black tea infusions using the taste activity concept

The contribution of theaflavins to the astringent taste of black tea infusions has been investigated. The major benzotropolons theaflavin, theaflavin-3-gallate, theaflavin-3′-gallate, theaflavin-3,3′-digallate, and theaflavic acid were synthetically prepared by enzymatic oxidation of binary mixtures of the corresponding flavan-3-ols, purified by high-speed countercurrent chromatography, and then sensorially evaluated by means of a comparative duo test. The sensory analysis revealed that the theaflavins imparted a mouth-coating, astringent, and long-lasting oral sensation at the very back of the throat, and demonstrated the theaflavins to have by far lower oral thresholds than the astringent catechins; for example, the threshold concentration of theaflavin (0.016 mmol/L) is by a factor of 33 and 58 lower than those of its precursors epigallocatechin and epicatechin, respectively. In order to study the importance of these theaflavins as contributors to tea astringency, these benzotropolons were quantified in tea infusions and taste activity values were calculated from the quotient of their concentration in tea and their taste detection thresholds. Relating the taste activity values of the individual theaflavins to the overall astringency of the teas revealed that the theaflavins accounted for less than 0.1% of the overall astringency of the teas investigated. In consequence, the theaflavin concentration seems not to be a suitable measure for taste quality of tea infusions.