The role of (−)‐epicatechin and polyphenol oxidase in the coupled oxidative breakdown of theaflavins

Abstract

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.

A tandem mass spectrometry method based on selected ions detects low‐abundance phenolics in black tea – theatridimensins as products of the oxidative cascade

“…). Upon coupled oxidation, a redox reaction occurs in which the EC‐quinone reduces back to EC while oxidizing TF into TNQ, a dimeric flavonoid in which the EC‐quinone is not incorporated. TNQ is considered an oligomerization product in the ‘oxidative cascade hypothesis’.…”

Secondary Metabolites in Fruits, Vegetables, Beverages and Other Plant‐based Dietary Components

“…The primary substrates for polyphenol oxidase are the flavan-3-ols which are converted to quinones. These quinones react further, and may be reduced back to phenols by oxidizing other phenols, such as gallic acid, flavonol glycosides and theaflavins, that are not direct substrates for polyphenol oxidase (Opie et al 1993(Opie et al , 1995.…”

Influence of polyphenol oxidase, peroxidase and organic acids on thein vitroiron bioavailability in faba bean flour

“…A hydroxycinnamic acid, for example, can trigger the oxidation of the more complex polyphenol by a coupled redox reaction. This has been shown, e.g., in procyanidins (Cheynier & da Silva, 1991) and theaflavins (Opie, Clifford, & Robertson, 1993).…”