Study into the chemical changes of tea leaf polyphenols during japanese black tea processing

Abstract

During the processing of black tea, enzymatic oxidation converts tea catechins into a complex mixture of oxidative products, including theaflavins, and thearubigins. In this study, ultra-performance liquid chromatography was carried out to analyze the tea extracts collected after each processing stage to clarify the quantitative changes in these compounds during black tea processing. It was found that the catechin content was significantly reduced during processing, and in particular between the later rolling and fermentation periods. In contrast, the variation in the theaflavin content was negatively correlated with the catechin content. Twenty-three compounds containing the known catechins dimers and flavonol glycosides were identified by liquid chromatography-mass spectrometry (LC-MS). In addition, 45 components whose contents increased significantly between the late rolling and late fermentation stages were extracted using principal components analysis by LC-MS. It was considered that due to the catechin-like units present in these components, they likely contribute to thearubigin production during black tea processing.

Keywords: Black tea processing; Oxidation; Principal component analysis; Tea catechins, UPLC-MS; Thearubigin.