Directional modulation of flavor and quality in primary dark tea using Aspergillus chevalieri fermentation: Insights from multi-platform metabolomics

Primary dark tea quality determines the final quality of dark tea, with microbial fermentation playing a crucial role in shaping its distinctive flavor profile. This study screened Aspergillus chevalieri ( A. chevalieri ) from Liupao tea and applied it to the intensified fermentation of primary dark tea. Sensory evaluation showed that the 15-day-fermented primary dark tea had optimal quality, with a rich woody-fungal aroma and a mellow, smooth taste. HS-SPME-GC-MS revealed major volatiles including hydrocarbons, alcohols, and aldehydes; floral β-ionone and woody α-cadinene significantly increased at 15 days, while off-flavor 1-octen-3-one decreased. Non-volatile metabolome analysis via UPLC-MS revealed elevated levels of sweet-tasting compounds (e.g., D-pyroglutamic acid, dihydroquercetin) and marked declines in bitter/astringent compounds (e.g., L-tryptophan, epigallocatechin gallate). These changes are primarily associated with amino acid biosynthesis and flavonoid degradation pathways. These results indicate that A. chevalieri -mediated intensified fermentation significantly improves primary dark tea quality, offering a new strategy for targeted quality regulation.