Stability of Black Tea Polyphenol, Theaflavin, and Identification of Theanaphthoquinone as Its Major Radical Reaction Product
摘要:
In the current study, we have focused on isolation and detection of major radical oxidation products from theaflavin in order to better understand antioxidation mechanisms of this compound. Theanaph-thoquinone was identified as a major oxidation product of theaflavin from two different oxidant model systems: DPPH and peroxidase/hydrogen peroxide. This result indicated that the benzotropolone moiety in theaflavin may play an important role in its antioxidant properties. The stability of theaflavin was studied in varying pH solutions: simulated gastric juice and buffer solutions of pH 5.5, pH 7.4, and pH 8.5. The results indicated that theaflavin is unstable in alkaline conditions, while it was stable in acidic conditions. Theanaphthoquinone was identified as an autoxidation product of theaflavin during its stability study in alkaline conditions.
A tandem mass spectrometry method based on selected ions detects low-abundance phenolics in black tea - theatridimensins as products of the oxidative cascade
作者:Annewieke J. W. Verloop、Jean-Paul Vincken、Harry Gruppen
DOI:10.1002/rcm.7658
日期:2016.8.15
Mixtures of phenolics are widespread in plant‐derived food products, for instance black tea. Detailed compositional analysis of phenolics present is important for quality control. Characterization of low‐abundance compounds often requires extensive purification; hence, the need for rapid screening methods to annotate compounds in complex mixtures without extensive sample preparation. Opportunities
leaves. In citrate–phosphate buffer solution at pH 6 and room temperature, TNQ reacted nonenzymatically with EGCg to afford three products, whose structures were determined on the basis of spectroscopic data. The results indicated that the double bond of the ortho-naphthoquinone moiety in TNQ reacted with the autoxidation product of EGCg. This study demonstrates novel reactions occurring in the process
Degradation of the black tea Pigment theaflavin was examined in detail. Enzymatic oxidation of a mixture of epigallocatechin and epicatechin initially produced theaflavin, while prolonged reaction decreased the product. Addition of ethanol to the reaction mixture at the point when theaflavin began to decrease afforded four new products, together with theanaphthoquinone, a known oxidation product of theaflavin. The structures of (he new products were determined by spectroscopic methods. One of the products was an ethanol adduct of a theanaphthoquinone precursor, and this reacted with theaflavin to give two further products. A product generated by coupling of theaflavin with epicatechin quinone was also obtained. The Structures of the products indicate that oxidation and coupling with quinones are key reactions in the degradation of theaflavins. The degradation of theaflavin probably contributes to production of thearubigins.
Oxidation mechanism of black tea pigment theaflavin by peroxidase
A large number of black tea polyphenols remain uncharacterized because of the complexity of catechin oxidation reactions that occur during tea fermentation. In the course of our studies on black tea polyphenols, we examined the enzymatic degradation of theaflavins, which are black tea pigments having a benzotropolone chromophore. Oxidation of theaflavin with peroxidase afforded a new product named theacoumarin A together with known pigment theanaphthoquinone. The structure of the new compound was determined by spectroscopic examination and a production mechanism via theanaphthoquinone is proposed. (C) 2015 Elsevier Ltd. All rights reserved.
Synthesis of Theaflavin from Epicatechin and Epigallocatechin by Plant Homogenates and Role of Epicatechin Quinone in the Synthesis and Degradation of Theaflavin
Oxidation products of (-)-epicatechin and (-)-epigallocatechin by treatment with homogenates of 62 plants belonging to 49 families were compared, Forty-six plants were capable of synthesizing theaflavin, a black tea pigment, regardless of whether they contained catechins. Loquat, Japanese pear, and blueberry had activities higher than that of fresh tea leaves after 5 h of treatment; furthermore, these plants oxidized theaflavin to theanaphthoquinone. An additional new metabolite, dehydrotheasinensin, was generated on treatment with fresh tea leaves, eggplant, and unripened Japanese orange. Evidence for the oxidation of epigallocatechin and theaflavin by electron transfer to epicatechin quinone was demonstrated in a time course study using bananas and trapping the quinone intermediates as glutathione conjugates.