Withering degree affects flavor and biological activity of black tea: A non-targeted metabolomics approach

This study focused on non-targeted metabolomics analysis of the relationship of the chemical composition, quality traits, bioactivity of black tea (Camellia sinensis L.) with five withering degrees (WD65, WD60, WD55, WD50, and WD45, corresponding to 65, 60, 55, 50, and 45% water content in withered leaves, respectively) and their effects on sensory quality traits. WD60 was shown as the optimal withering degree (WD) with the highest total quality score (89.7), followed by WD55 (88.7). With increasing WD, the content of most volatile components increased significantly, but with no significant difference between some substances below WD55. The total amount of free amino acids increased with increasing WD, in contrast to a decrease in the total amount of catechins, flavonoids/flavonoid glycosides, theaflavins and glycosidically bound volatiles (GBVs). Black tea with a WD between WD65 and WD60 was shown to have higher antioxidant activity and stronger inhibitory effect on alpha-amylase and alpha-glucosidase activity or intestinal glucose uptake. The overall data indicate that WD60 treatment not only benefits the formation of sensory quality traits, but also shows better bioactivity.