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

✍ Scribed by Wan, Xiaochun; Nursten, Harry E; Cai, Ya; Davis, Adrienne L; Wilkins, John P G; Davies, Alan P

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 326 KB
• Volume: 74
• Category: Article
• ISSN: 0022-5142
• DOI: 10.1002/(sici)1097-0010(199707)74:3<401::aid-jsfa816>3.0.co;2-j

✦ Synopsis

Epicatechin-3-O-gallate (ECG), one of the major green tea polyphenols, was oxidised chemically using potassium ferricyanide. The major oxidation product, termed theaÑavate A, which gave a sharp peak on HPLC analysis, was separated and puriÐed 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 Ñavan-3-ols participate in oxidative condensation reactions. This illustrates the complexity of theaÑavin-type compounds in black tea and provides an additional reaction pathway for the formation of thearubigins which has not been previously considered.