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

Abstract

( - )-Epicatechin-3-O-gallate (ECG), one of the major green tea poly-phenols, was oxidised chemically using potassium ferricyanide. The major oxidation product, termed theaflavate A, which gave a sharp peak on HPLC analysis, was separated and purified by a combination of chromatography on Sephadex LH-20 and a semi-preparative HPLC method. This compound was characterised by NMR spectroscopy (1H, 13C, HMQC, HMBC and ROESY) and mass spectrometry (Electrospray method) and was found to have a novel benzotropolone skeleton formed between the B-ring of one ECG molecule and the galloyl ester group of another. Compounds containing this type of benzotropolone link were also found to be present in black tea. This benzotropolone link is of great interest, since it shows that the galloyl ester groups of flavan-3-ols participate in oxidative condensation reactions. This illustrates the complexity of theaflavin-type compounds in black tea and provides an additional reaction pathway for the formation of thearubigins which has not been previously considered. © 1997 SCI