The Oxidation Mechanism of Flavan-3-ols by an Enzymatic Reaction Using Liquid Chromatography–Mass Spectrometry-Based Metabolomics Combined with Captured o-Quinone Intermediates of Flavan-3-ols by o-Phenylenediamine

Abstract

During the enzymatic oxidation of black tea, flavan-3-ols undergo a complicated chemical transformation and generate theaflavins and thearubigins. So far, the oxidation mechanism of flavan-3-ols has not been clarified. Liquid chromatography–tandem mass spectrometry-based metabolomics combined with o-quinone intermediates captured by o-phenylenediamine was developed and successfully applied in the liquid incubation of fresh tea homogenates. During the oxidation, the contents of catechins continuously decreased, while theaflavins increased first but decreased subsequently at the end of incubation. Meanwhile, the content of thearubigins greatly increased at the late stage of incubation. Dehydrotheasinensins were accumulated at the end of oxidation along with the decrease of theasinensins. Through o-phenylenediamine derivation, several adducts of (−)-epigallocatechin gallate, (−)-epigallocatechin, theasinensins A, B, C, and D, and corresponding dehydrotheasinensins were identified, which were considered as the substrates of thearubigins. These results suggested that theaflavins and these oxidation products contributed to the formation of thearubigins.

Heavy Metals, Their Phytotoxicity, and the Role of Phenolic Antioxidants in Plant Stress Responses with Focus on Cadmium: Review

“…It has also been reported that flavan-3ols found in tea plants, which are characterized by their meta-5,7-dihydroxy-substituted A-ring and catechol or pyrogallol B-ring, can easily be oxidized. This mechanism was studied in great detail [174]. The auto-oxidation of catechins, catalyzed by the endogenous enzymes polyphenol oxidase and peroxidase, can take place even when the enzymes are inactivated or removed.…”

Efficient enzymatic synthesis of theaflavin and its production mechanism

“…Black tea, being the most consumed type of tea in the world, accounts for 80% of the global tea consumption (Kusano et al., 2015; Zha et al., 2022). Theaflavins (TFs), as the primary components of black tea, play a crucial role in the grade and quality of black tea, determining its color, brightness, strength, and briskness (Samanta et al., 2015).…”