THE ROLE OF (-)-EPICATECHIN AND POLYPHENOL OXIDASE IN THE COUPLED OXIDATIVE BREAKDOWN OF THEAFLAVINS

An enzymic in-vitro model tea fermentation system has been used in combination with gradient elution reversed-phase HPLC to study the oxidative breakdown of black tea theaflavins in the presence and absence of (-)-epicatechin. It was found that theaflavin, theaflavin-3-monogallate, theaflavin-3'-monogallate and theaflavin-3,3'-digallate were not substrates for tea polyphenol oxidase (EC 1.14.18.1) whereas (-)-epicatechin alone, or mixtures of (-)-epicatechin and a theaflavin were rapidly converted to a complex mixture of thearubigin-like substances. While the chromatographic profiles varied with the identity of the theaflavin precursor each resembled the equivalent profile obtained with a whole black tea liquor. It is concluded that theaflavins are degraded by a coupled oxidation with (-)-epicatechin-quinone. It is suggested that thearubigins may form via these pathways during black tea manufacture.