A study on the change of enantiomeric purity of catechins in green tea infusion

The enantiomeric composition of catechin in commercial tea beverages differs markedly from that in freshly brewed tea. We attempt to determine the cause of this difference by measuring the change in the ratios of catechins relative to (+)-catechin with time. When tea extracted with water was heated to 80 °C, (−)-epicatechin and (−)-epicatechin gallate epimerized to (−)-catechin and (−)-catechin gallate, respectively. When the thermal sterilized tea extracts were left at room temperature in the dark, it was recognized that the hydrolysis of the gallate moiety proceeded in parallel with epimerization. The hydrolysis of (−)-catechin gallate to (−)-catechin was a major pathway in the tea extracts that were not subjected to heat-treatment. Consequently, it appears that the simultaneous progression of the epimerization during thermal sterilization and the hydrolysis during distribution and storage increases the proportion of (−)-catechin ratio in the commercial tea beverages.