Microbial transformation of Apocynum venetum L. tea by Eurotium cristatum during solid-state fermentation: Insights...

Fermentation by food microorganism provides an effective approach for transforming plant-based substrates, yet the microbial mechanisms underlying these biochemical processes remain insufficiently understood. In this study, Eurotium cristatum-mediated solid-state fermentation of Apocynum venetum L. tea (AVL) was investigated at 2, 4 and 6 days using an integrated multi-omics approach and sensory-related analyses. Fermentation decreased bitterness and astringency of AVL infusions, accompanied by reductions in total polyphenols and flavonoids. Untargeted metabolomics identified 41 core differential non-volatile metabolites, predominantly fatty acyls, glycerophospholipids, steroids, phenolics, and terpenoids. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment highlighted phenylpropanoid-, flavonoid-, and isoflavonoid-related pathways. Volatile profiling identified 16 aroma-active compounds. Changes in aldehydes, ketones, alcohols, and esters contributed to fermentation-associated aroma characteristics. Metaproteomic analysis identified 4614 E. cristatum proteins, including 1838 differential proteins enriched in functional categories related to catalytic activity, oxidoreductase activity, glycosyl bond hydrolase activity, carbohydrate metabolism, and secondary metabolism. Integrated multi-omics analysis showed that non-volatile metabolite remodeling was associated with multiple microbial functional modules related to carbon metabolism, redox reactions, and secondary metabolism while fatty acid and amino acid metabolism were associated with the formation of characteristic aroma-active compounds. Overall, E. cristatum-mediated fermentation of AVL represents a growth-coupled, enzyme-associated biotransformation process in which coordinated microbial metabolic activities contribute to metabolites remodeling and the development of characteristic taste and aroma properties. These findings provide a mechanistic basis for understanding E. cristatum-mediated transformation of plant substrates and offer insights into the formation of characteristic quality attributes during fermented tea production.