Preparation of epimers of tea catechins by heat treatment

Products from tea catechins ((+)-catechin, (-)-epicatechin, (-)-epigallocatechin, (-)-epicatechin gallate, and (-)-epigallocatechin gallate) after heat treatment were individually isolated by preparative HPLC and subsequent crystallization. FAB-MS, elemental, H-1- and C-13-NMR, and optical rotation analyses indicated these products to be the C-2 epimers of the original catechins. The effects of temperature, time, pH, and concentration an this conversion of tea catechins to their epimers were examined. It was determined that the epimerization reaction should be conducted with 1% each of the tea catechin solution (pH 5) at 120 degrees C for 30 min.