Oxidation of tea polyphenols promotes chlorophyll degradation during black tea fermentation

The color of black tea is directly affected by chlorophyll degradation during fermentation. In this study, the content of chlorophyll and its derivatives during fermentation was determined by HPLC, and chlorophyll a and b were shown to decrease significantly (44.23% and 24.24%). By analyzing the activity of chlorophyllase (CLH), magnesium dechelatase (MDcase) and pheophorbide a oxygenase (PAO), the key enzymes of chlorophyll degradation, as well as changes of tea polyphenols, tea pigments, pH, ROS and other physicochemical indexes, polyphenol oxidation rather than enzymatic catalysis was found to be the main cause of chlorophyll degradation. In vivo and in vitro verification tests showed that the chlorophyll structure was directly disrupted by the oxidation of polyphenols, and chlorophyll degradation was further promoted by ROS generated during oxidation, reduction of o-quinone, and pH decrease. This study provided a theoretical basis for improving the color quality of black tea.