Gut Microbiota-Mediated Liberation of Ellagic Acid from Strawberry Soluble Fiber and Its Metabolism: In Vitro and In Vivo Evidence

This study investigated strawberry soluble fiber (SSF) as a reservoir of celobiotics and evaluated their microbial liberation and metabolism both in vitro and in vivo. In vitro colonic fermentation of SSF combined with untargeted metabolomics identified urolithin C/iso-urolithin C, a gut microbial metabolite derived exclusively from ellagic acid (EA), suggesting the microbial liberation of matrix-embedded EA from SSF. This hypothesis was validated by pectinase treatment, which increased total EA equivalents by approximately 10-fold. Time-course fermentation demonstrated rapid EA liberation from SSF and its subsequent urolithin conversion, which was further confirmed in human-microbiota-transplanted mice after SSF consumption in vivo. Notably, substantial interindividual variation was observed in the capacities of human fecal microbiota to release EAs and produce urolithins. Beyond SSF, EA is widely distributed among plant-derived dietary fibers (DFs) and is particularly abundant in berry fibers. This work expanded the celobiotic concept and highlighted the importance of the microbiota-mediated release of hidden phytochemicals from dietary fibers.