The formation of thearubigin‐like substances by in‐vitro polyphenol oxidase‐mediated fermentation of individual flavan‐3‐ols

An enzymic in‐vitro model tea fermentation system has been used in combination with gradient elution reversed‐phase high‐performance liquid chromatography to study the formation from individual fiavan‐3‐ols of resolvable and unresolvable thearubigin‐like substances. It has been found that in 30 min at pH 5.6 tea polyphenol oxidase (EC 1.14.18.1) produces a distinctive range of resolvable thearubigin‐like products from each flavan‐3‐ot substrate examined ((+)‐catechin, (−)‐epicatechin, (−)‐epigallocatechin, (−)‐epicatechin gallate and (−)‐epigallocatechin gallate). However, (−)‐epicatechin, and to a much lesser extent (+ )‐catechin, were the only flavan‐3‐ols converted to an unresolvable thearubigin‐like hump under these conditions. In addition, it was demonstrated that varying the pH of incubation in the range 5.0–6.0 had little effect on the profile of products obtained from the simple catechins, but a pronounced effect in the case of the gallocatechins. It is concluded that the combination of (−)‐epicatechin and polyphenol oxidase is the simplest model of tea fermentation that can be used to generate in quantity thearubigin‐like materials for structure elucidation.