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.