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Abstract: Following the oxidation of epicatechin (EC), three novel compounds and two known compounds were isolated. The chemical structures of these oxidation products were determined by mass spectrometry (MS) and various nuclear magnetic resonance (NMR) experiments, and the A-ring-B-ring linkage that is characteristic of catechin was found in each molecule. Three compounds showed similar ultraviolet-visible (UV-Vis) spectra to EC, whereas two compounds showed different spectral absorption in the region between 300 and 500 nm. A similar spectrum was obtained for the thearubigin fraction prepared from a black tea infusion. This result suggests that the condensation reaction between the A-ring and B-ring is more important than reaction between B-rings for thearubigin formation. [ABSTRACT FROM AUTHOR]

Tea (Camellia sinensis, Theaceae) is one of the most widely consumed beverages in the world. The three major types of tea, green tea, oolong tea, and black tea, differ in terms of the manufacture and chemical composition. Catechins, theaflavins, and thearubigins have been identified as the major components in tea. Other minor oligomers have also been found in tea. Different kinds of ring fission and formation elucidate the major transformed pathways of tea catechins to their dimers and polymers. The present review summarizes the data concerning the enzymatic oxidation of catechins, their dimers, and thearubigins in tea. [ABSTRACT FROM AUTHOR]