A New Type of Tea Pigment—From the Chemical Oxidation of Epicatechin Gallate and Isolated from Tea

Comparative studies on the physicochemical and antioxidant properties of different tea extracts

“…The hydrogen peroxide oxidized tea polyphenols (named as HOP) was obtained by drying the ethyl acetate extract in vacuum and freeze-dried. Chemical oxidation of green tea extracts by potassium hexacyanoferrate was done according to Wan et al (1997) and the potassium hexacyanoferrate oxidized tea polyphenols (named as POP) were obtained.…”

Polymer-Like Polyphenols of Black Tea and Their Lipase and Amylase Inhibitory Activities

“…This observation suggested that significant amounts of the galloyl groups were oxidized during production of the polymeric substance. The major product of the reaction was theaflavate A (10), 25) which is a dimer produced by intermolecular oxidative condensation between the catechol B-ring and the galloyl group (Chart 1). In addition, theaflavate C (11), an extended trimer of 2, was isolated from the same reaction mixture.…”

Structures of Epicatechin Gallate Trimer and Tetramer Produced by Enzymatic Oxidation

“…Products were separated by repeated column chromatography using Sephadex LH-20 and Chromatorex ODS to give two new compounds named theaflavate C (3) and bistheaflavate A (4), together with a known pigment 2. Pigment 2 was the major product of the reaction and identified to be theaflavate A, 24) which was generated by intermolecular oxidative coupling of the galloyl group and catechol B-ring of 1. The presence of 2 in commercial black tea was previously confirmed by HPLC analysis.…”

“…[13][14][15][16][17][18][19][20][21][22] On the other hand, 60-80% of the total tea catechins possess galloyl esters located at the C-3 hydroxy group and although oxidation of galloyl groups must be important in the formation of black tea polyphenols, 23) only limited examples of oxidative coupling of galloyl groups has been reported. 22,[24][25][26] Our previous in vitro experiments showed that enzymes preferentially oxidize the catechol B-rings of epicatechin and the resulting quinone, which is a potential oxidizing reagent, subsequently oxidizes pyrogallol rings, the redox potential of which is lower than that of the catechol ring.…”