Fermentation with Aspergillus cristatus Changed the Volatile Compounds and Metabolites of Fu-Brick Tea: Insights from Aroma Profiling and Widely Targeted Metabolomics

To investigate the influence of single fungi fermentation on dark tea, Aspergillus chevalieri and Aspergillus cristatus were isolated from Fu-brick tea in this study. Both strains were used for solid-state fermentation of Fu-brick tea to analyze volatile compounds, while A. cristatus was used for liquid-state fermentation to analyze metabolite changes. Solid-state fermentation with Aspergillus chevalieri and Aspergillus cristatus yielded 56 and 63 volatile compounds, respectively, with alcohols, aldehydes, and ketones as the predominant classes. Notably, A. cristatus biotransformation resulted in the highest total volatile content, primarily characterized by trans-linalool oxide, cis-linalool oxide, and dihydroactinidiolide. Conversely, Aspergillus chevalieri fermentation produced fewer aroma compounds, mainly trans-linalool oxide and dihydroactinidiolide. Widely targeted metabolomics further revealed that flavonoids, amino acids and derivatives, phenolic acids, lipids, and tannins were significantly reduced in the liquid-state-fermented tea leaves, whereas most differential metabolites accumulated in the tea infusions. Flavonoid biosynthesis and amino acid metabolism were identified as the most significantly enriched pathways. These findings elucidate strain-dependent divergence in aroma composition and non-volatile metabolite transformation, offering a scientific basis for targeted strain selection and process optimization in the development of industrial fermented tea products.