Microbial-enzymatic associations with a U-shaped sweet aroma trajectory and the progressive development of woody, herbal, and aged notes during long-term aging of Shoumei white tea.

Aroma is a critical determinant of quality in aged white tea; however, the microbial and enzymatic mechanisms associated with aroma evolution during aging remain unclear. An integrated analysis combining sensory evaluation, volatile profiling, and microbial profiling was conducted to investigate aroma evolution during long-term aging of Shoumei white tea. Sixty-six aroma-active compounds were identified, eleven of which were closely related to aroma evolution. Among them, eight showed U-shaped sweet aroma trajectory, whereas three were significantly correlated with progressively intensified woody, herbal, and aged notes. Volatiles with sweet and floral-fruity attributes were identified as candidate contributors to the U-shaped trajectory, while safranal and isophorone emerged as candidate aging-related aroma markers. Bacterial community composition remained relatively stable despite abundance fluctuations, whereas the fungal community showed a stage-dependent succession from Setophoma to Wallemia and finally to Aspergillus. Integrated network analysis revealed two modules linking differentially abundant microbial genera, key predicted enzyme functions, and characteristic volatiles. The sweet and floral-fruity module comprised five microbial taxa, five predicted enzyme functions, and eight volatiles showing U-shaped trends, potentially involving glycoside hydrolysis, ester-related transformation, and carotenoid- and oxidation-related pathways. In contrast, the module related to woody, herbal, and aged attributes comprised six microbial taxa, eleven predicted enzyme functions, and three progressively increasing volatiles, potentially involving terpenoid transformation and oxidative metabolism. These findings suggest that divergent aroma trajectories in aged Shoumei white tea are associated with distinct microbial-enzymatic modules, providing a basis for understanding aroma formation during long-term white tea aging.