In Vitro Fermentation of Green Tea by Human Gut Microbiota Enhances Bioactivity and Bidirectionally Modulates Polyphenol Metabolites and Gut Microbiota

Green tea is highly popular due to its richness in polyphenols exhibiting broad bioactivities. Tea polyphenols, primarily catechins and flavonoids, demonstrate health benefits following biotransformation by the gut microbiota to overcome limited bioavailability. However, metabolites and interaction between green tea polyphenol and the gut microbiota remains to be fully elucidated. This study investigates the biotransformation of metabolites and interaction between human gut microbiota (HGM) and green tea extract (GTE) through in vitro anaerobic fermentation. Temporal bioactivity assessments demonstrated that fermentation-enhanced antioxidant capacity and inhibition potential of α-glucosidase, α-amylase and pancreatic lipase peak at 6 h, showing strong correlations with polyphenol and flavonoid biotransformation kinetics. Using the untargeted metabolomics approach, 55 characteristic differential compounds during the fermentation process in GTE were characterized, including 15 catechins, 29 flavonoids, five organic acids and six other phytochemicals. Furthermore, nine microbial-transformed metabolites derived from GTE flavonoids were identified and the corresponding metabolic pathways were proposed simultaneously. Analysis of 16S rRNA gene sequencing revealed that GTE significantly enhanced gut microbiota diversity and induced structural reorganization, specifically enriching genera such as Bacteroides, Bifidobacterium, Lactococcus and Enterococcus, which are likely involved in flavonoid biotransformation of GTE. Thus, the findings provide new insights for elucidating microbiota-mediated metabolites of green tea polyphenol, and their bidirectional interactions in the human gut.