Production and degradation mechanism of theacitrin C, a black tea pigment derived from epigallocatechin-3-O-gallate via a bicyclo[3.2.1]octane-type intermediate

Black tea is rich in polyphenols and has been shown to have various health benefits; however, its components have not yet been clarified in detail. Enzymatic oxidation of epigallocatechin-3-O-gallate, the most abundant polyphenol in tea, is thought to contribute significantly to the production of black tea polyphenols. We identified theacitrin C, an unstable black tea pigment, as an enzymatic oxidation product of epigallocatechin-3-O-gallate. Degradation of theacitrin C afforded theacitrinin A and 2,3,5,7-tetrahydroxychroman-3-O-gallate. Furthermore, theacitrinin B, which was isolated from black tea, is deduced to be a degradation product of theacitrin A, the desgalloyl analogue of theacitrin C. The structures of theacitrinins A and B were elucidated based on spectroscopic data. This is the first time that a degradation product of theacitrin has been isolated from black tea. We also examined the influence of esterification of the epigallocatechin C-3 hydroxyl group on the decomposition of bicyclo[3.2.1]octane-type intermediates.