New browning reaction of tea polyphenols during the roasting process of green tea leaves

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Green tea is produced from the leaves of Camellia sinensis. Some green tea products are further roasted to add a characteristic flavor. By roasting, color of the tea leaves changes from green to reddish brown, and the amount of catechins, amino acids, and free sugars decreased. However, details of the chemical reactions of catechins on roasting still are not clarified. In this study, we demonstrated that epigallocatechin-3-O-gallate reacted with theanine and glucose to afford condensation products. Epigallocatechin-3-O-gallate was heated at 150℃in the presence of theanine to yield six new compounds. Two products are red pigments having p-quinone structure, and the production of these pigments may explain the color change of tea leaves by roast treatment. On the other hand, heating of mixtures of epigallocatechin-3-O-gallate, theanine, and glucose at 150℃afforded two products. These products are considered to be produced by condensation of 1-ethyl-5-hydroxy-2-pyrrolidinone, which is produced by Strecker degradation of theanine, with epigallocatechin-3-O-gallate at the A-ring 8 and 6 positions.