Polyphenol Bioconversion and Volatile Aroma Production by Meyerozyma sp. C3 Isolated from Kombucha in the Theaflavin–Sucrose Fermentation Model

This study integrated metagenomic and untargeted metabolomics analysis to characterize differences in kombucha communities and metabolites between black tea–sucrose and theaflavin–sucrose systems. Theaflavins selectively enriched yeasts, particularly Meyerozyma and Lodderomyces, and increased the annotated abundance of carbohydrate-metabolism genes, glycoside hydrolases, and glycosyltransferases. Based on these community-level findings, the newly isolated Meyerozyma sp. C3 was employed to establish a simplified single-strain fermentation model to investigate the biotransformation potential of the enriched yeast taxon. The strain exhibited stable growth and sustained acidification throughout fermentation, with a theaflavin conversion rate of 39.5% after 7 days. Metabolomic analysis revealed substantial changes in oligosaccharides (e.g., maltotriose, raffinose), flavonoids/flavanes (e.g., epigallocatechin gallate, (+)-gallocatechin, (-)-epigallocatechin, and catechin derivatives), and organic acids (e.g., citric and isocitric acid), while volatile profiling identified 2-phenylethanol and 4-ethylphenol as newly dominant aroma compounds after fermentation. These results indicate that a yeast-driven route for theaflavin transformation and flavor formation, supporting targeted strain mining and functional fermented-tea development.