Enhancing black tea quality through shaking: Integrated metabolomic and transcriptomic analysis reveals the mechanism of shaking on quality-related components during tea processing

Abstract

The quality differences between traditional black tea (NS) and shaken black tea (S), as well as the specific effects of shaking on quality-related metabolites and gene regulation in black tea, remain unclear. This study found that mechanical disruption during shaking facilitates the release of cellular contents, enhances polyphenol oxidase (PPO) gene expression levels, and modulates the synthesis of theanine, phenolic acids and proanthocyanidins as well as flavonoid metabolism, thereby promoting the accumulation of theanine (increased by 87.17 % in S vs NS), theaflavins (21.50 %), phenolic acids (19.14 %), proanthocyanidins (17.67 %), and flavonoid glycosides (13.52 %). This deepened infusion color and made its taste more smooth, thick, and mellow, thereby improving its taste and infusion color quality. Furthermore, shaking upregulates terpene synthase (TPS) gene expression and promotes volatile release through modulation of terpenoid, fatty acid, and amino acid metabolic pathways. However, the structural damage to tea leaves leads to a relatively low retention rate of volatile components in the finished tea. This phenomenon enhances the overall floral and sweet attributes of the tea, thereby improving its aroma quality. This study systematically elucidates the molecular mechanisms underlying the effects of shaking on black tea quality formation, filling the research gap regarding the relationship between mechanical disruption during shaking and quality-related metabolic regulation. Furthermore, it provides both theoretical foundations and technical guidance for the targeted and standardized processing of high-quality black tea.