HPLC-MS/MS Quantification of Flavan-3-ols, Xanthines, and Epigallocatechin-3-Gallate Oxidation Products in Tea Samples and New Insights into Their Cytotoxicity

Infusions of the tea plant Camellia sinensis L. have been intensively studied regarding their constituents and especially their bioactivity. While the compound classes of catechins and xanthines are strongly associated with tea, tea consumption as a source for oxidation products based on the flavan-3-ol epigallocatechin gallate (EGCG) is rather unknown. The formation of theasinensins, which represent flavan-3-ol dimers, was already observed under cell culture conditions and also occurs during tea fermentation and brewing. However, oxidation product contents in tea infusions and their bioactive effects have not yet been sufficiently evaluated. In this study, flavan-3-ols, xanthines, and EGCG oxidation products were quantified in 26 tea samples of different fermentation degrees via validated high-performance liquid chromatography coupled with tandem mass spectrometry. Lastly, the cytotoxicity of these oxidation products on HepG2 hepatocarcinoma cells was examined. As a result, theasinensin A was found as an abundant oxidation product in fermented teas with higher cytotoxic potential in comparison to its parental EGCG.