Bioactive release and modulation of urolithin metabotype A phenotype gut microbiota during in vitro digestion and fermentation of ellagic acid-rich fruit polyphenols

Abstract

Ellagic acid-rich fruits (EARF) are valued for their bioactive compounds, yet their gastrointestinal biotransformation remains insufficiently understood. This study investigated the functional transformation of phytochemicals, antioxidant effects, and microbial shifts related to the urolithin metabotype-A phenotype during simulated gastrointestinal digestion and colonic fermentation of four freeze-dried EARF powders: raspberry (RA), strawberry (ST), Chinese chestnut (CC), and pomegranate (PO). Simulated digestion markedly decreased the phenolic content in all groups, which was strongly associated with reduced antioxidant capacity. Across all groups, 24 phenolics were found, and the levels of most compounds dropped notably after digestion. Fecal microbiota from urolithin-A producers fermented the digested powders, resulting in increases in beneficial bacteria like Bifidobacterium and elevated short-chain fatty acids (SCFAs) production. Lactobacillus was identified as a key contributor to EA metabolism and Uros production. Functional prediction analysis revealed distinct functional enrichments among EARF powders, corresponding to their compositional differences. Among the groups, ST and RA retained higher phenolic levels, which contributed to their stronger antioxidant capacity, while PO more effectively promoted SCFAs production. All groups demonstrated distinct modulation of gut microbiota composition. The results underscore the value of EARF powders as functional foods capable of improving gut health by modulating the microbiota and promoting the generation of beneficial metabolites.