STABILIZING EFFECT OF ASCORBIC-ACID ON GREEN TEA CATECHINS

Green tea catechins (GTCs) as a mixture of (-)-epicatechin (EC), (-)-e picatechin gallate (ECG), (-)-epigallocatechin (EGC), and (-)-epigallo catechin gallate (EGCG) possess a variety of biological activities. We have previously studied the stability of GTCs either as a mixture or as individual epicatechin derivatives in various pH, demonstrating tha t GTCs as a mixture in alkaline solutions were extremely unstable and degraded almost completely in a few minutes, whereas in acidic solutio ns (pH < 4) they were very.stable. For the pH ranging from 4 to 7, the stability of GTCs was inversely associated with the pH value of the i ncubation solutions. The present study examined the effect of ascorbic acid and citric acid on the stability of GTCs incubated in sodium pho sphate buffer (pH = 7.42). Ascorbic acid added to the incubation mixtu re significantly increased the stability of GTCs whereas citric acid e xhibited no effect. Four epicatechin derivatives examined demonstrated varying stability, with EGCG and EGC being equally instable and EC an d ECG being relatively stable. The addition of ascorbic acid significa ntly increased the stability of all four derivatives, particularly EGC and EGCG. The present results, although not directly transferable to in vivo conditions, may suggest that the presence of ascorbic acid may stabilize the GTCs in the intestine where the pH is neutral or alkali ne before absorption.