Nonvolatile metabolite alterations during Zijuan black tea processing affect the protective potential on HOECs exposed to nicotine.

Understanding nonvolatile metabolite alterations during processing and their impacts on potential function is crucial for technological innovations in tea manufacturing. In the present work, specific metabolite alterations during Zijuan black tea processing and their potential effects on nicotine-induced human oral epithelial cell (HOEC) injury were investigated. The results showed that leucine, isoleucine, and tyrosine were the main hydrolysis products during withering, and theaflavin-3-gallate (TF-3-G), theaflavin-3'-gallate (TF-3'-G) and theaflavin-3,3'-gallate (TFDG) were mainly formed during rolling. Moreover, oxidation of flavonoid glycosides, catechins and dimeric catechins took place during fermentation. During drying, amino acid conversion became dominant. Meanwhile, processing samples effectively attenuated nicotine-induced oxidative stress and inflammation in HOECs. TF-3'-G, TF-3-G, phenylalanine, and kaempferol-3-coumaroylglucoside exhibited strong associations with protective action, which indicates that modifying the processes in which black tea are produced to be rich in those specific components could be beneficial for the oral health of people who smoke.