THE CHEMICAL OXIDATION OF CATECHINS AND OTHER PHENOLICS - A STUDY OF THE FORMATION OF BLACK TEA PIGMENTS

The chemical oxidation of polyphenols has been used to produce black t ea pigments. (+)-Catechin, (-)-epicatechin, (-)-epicatechin gallate an d (-)-epigallocatechin gallate were isolated from convenient sources, their identity being confirmed by mass spectrometry and HPLC. The oxid ation of a mixture of (-)-epicatechin gallate and gallic acid gave an oxidation product of (-)-epicatechin gallate in addition to epitheafla vic acid 3-gallate. The catechins were oxidised chemically and the pro ducts analysed by HPLC, the chromatograms being compared with a black tea chromatogram. The reactions gave both resolved and unresolved pigm ents, and many of the resolved pigments had HPLC retention times close to black tea pigments. Each catechin behaved differently, the chromat ograms of the oxidation products from each starting material being cle arly distinguishable. Resolved pigments were obtained by the chemical oxidation of other phenolic compounds. This work provides a convenient method for studying the formation of resolved and unresolved black te a pigments.