The chemical oxidation of catechins and other phenolics: A study of the formation of black tea pigments

Abstract The chemical oxidation of polyphenols has been used to produce black tea pigments. (+)‐Catechin, (−)‐epicatechin, (−)‐epicatechin gallate and (−)‐epigallocatechin gallate were isolated from convenient sources, their identity being confirmed by mass spectrometry and HPLC. The oxidation of a mixture of (−)‐epicatechin gallate and gallic acid gave an oxidation product of (−)‐epicatechin gallate in addition to epitheaflavic acid 3‐gallate. The catechins were oxidised chemically and the products analysed by HPLC, the chromatograms being compared with a black tea chromatogram. The reactions gave both resolved and unresolved pigments, and many of the resolved pigments had HPLC retention times close to black tea pigments. Each catechin behaved differently, the chromatograms of the oxidation products from each starting material being clearly 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 tea pigments.