Study on improving aroma quality of summer-autumn black tea by red-light irradiation during withering

Red-light withering (RLW) was shown to improve the aroma of summer-autumn black tea, probably due to the increase in the content of main floral aroma components. Analysis of the dynamic changes of volatile components during withering showed that RLW mainly played a role in the late withering period. Non-target metabolomics and transcriptomics were used to analyze the main biosynthetic pathways of volatile components. RLW was shown to significantly up-regulate the expression of terpene synthesis-related genes (LIS, FAS, etc.) in the late withering stage and further promote the synthesis of volatile terpenoids (linalool and α-farnesene). Meanwhile, RLW leaves could release more leaf alcohol in the late withering period, due to the high expression of enzyme genes (LOX, ADH). Additionally, RLW could significantly increase the content of phenylethyl alcohol in the early withering stage. Moreover, the relative content of volatile bound glycosides (GBVs) did not change significantly among the three treatments (0 h, RLW9h and CK9h) after withering, suggesting that the hydrolysis of GBVs contributed little to aroma content during withering. Overall, RLW can significantly increase the activity of glycosidase in the later withering stage, thus improving the aroma quality of black tea in the subsequent processing.