Metabolomics and transcriptomics reveal the quality formation mechanism during the processing of black tea

The dynamic changes of metabolites and their regulatory mechanisms during black tea processing are not yet fully clear. In this study, flavonoid glycosides, tea pigments, VTs, and FADVs were primarily influenced. The content of these components continuously increased during processing, reaching their maximum after fermentation, and then decreased after drying. Withering upregulated AM and GT genes, promoting the glycosylation of flavonoids; the upregulation of ANR and PPO genes facilitated the oxidative polymerization of catechins; and the upregulation of TPS, LOX, and HPL genes promoted terpenoid synthesis and fatty acid degradation. This led to an increase in the content of these components in withered leaves. The accumulation of these components during fermentation was mainly due to the disruption of cells during rolling, allowing enzymes and substrates to fully integrate and react during the prolonged fermentation process. The decline in compound during the drying was primarily attributed to thermal degradation.