INFLUENCE OF PH ON THE ENZYMATIC OXIDATION OF (+)-CATECHIN IN MODEL SYSTEMS

PPO-catalyzed oxidation of (+)-catechin was performed in aqueous buffers in the pH range 3-7, using the same level of PPO activity at all pH values. Concentration of (+)-catechin and major oxidation products was monitored by HPLC. The nature and amounts of products formed were highly pH dependent. The solutions oxidized at pH below 4 contained mostly colorless products (lambda(max) 280 nm), whereas yellow compounds (lambda(max) 385-415 nm), eluting later than the colorless ones, predominated at higher pH values. Seven of them were purified by semipreparative HPLC. FAB-MS and acid hydrolysis data indicated they were dimers differing from natural procyanidins.