Enhancing chemical and aroma profiles of Fu brick tea via Bacillus licheniformis-mediated enhanced fermentation: evidence from targeted chemistry, volatilomics, and metagenomics.

Fu brick tea, a typical post fermented tea, derives its quality characteristics largely from microbial metabolism during the golden flower formation stage. To explore the application potential of functional microorganisms in Fu brick tea fermentation, this study systematically evaluated the effects of enhanced fermentation with Bacillus licheniformis across three substrates, including dark tea, golden flower loose tea, and Fu brick tea, with a particular focus on chemical composition, volatile flavor compounds, and sensory quality. The results demonstrated that B. licheniformis could stably colonize the solid state fermentation system of Fu brick tea and establish functional complementarity and metabolic synergy with Aspergillus cristatus without disrupting the fungus dominated microecological structure. Correlation, KEGG, and CAZy analyses revealed functional changes consistent with potential metabolic complementarity between these microorganisms. This synergistic interaction markedly accelerated the biotransformation of tea polyphenols and catechins, leading to a significant reduction in bitterness and astringency of the tea infusion. Meanwhile, volatile compounds associated with floral, fruity, fungal, and woody aroma attributes, such as phenethyl alcohol, geranyl acetone, and dihydroactinidiolide, were consistently enriched across different fermentation systems, promoting the development of more complex aroma profiles. Sensory evaluation further confirmed the positive role of B. licheniformis in enhancing aroma complexity, improving taste balance, and optimizing infusion color. Collectively, these findings highlight the promising application potential of B. licheniformis as a functional fermentation strain in the enhanced fermentation of Fu brick tea and provide a novel technical perspective for the directional fermentation and quality stabilization of post fermented teas.