Fucus vesiculosus Polysaccharide-Based Solid Dispersions Enhance Aqueous Dispersion and Gut Microbial Biotransformation of Ellagic Acid

Ellagic acid (EA) is a food-derived polyphenol with multiple biological activities, but its poor water solubility and aggregation in aqueous systems limit its accessibility to gut microorganisms. In this study,Fucus vesiculosuspolysaccharide (FVP) was used as a natural carrier to prepare EA/FVP solid dispersions (SDs) with different mass ratios by solvent-assisted evaporation. Compared with pure EA, the SDs markedly improved the apparent solubility and aqueous dispersion stability of EA. The highest apparent solubility was observed for the EA/FVP 3/1 formulation (0.75 ± 0.03 mg/mL), which was approximately 6.25-fold higher than that of pure EA (0.12 ± 0.01 mg/mL). The improved dispersion behavior was associated with increased apparent viscosity, reduced aggregation, decreased crystallinity and possible non-covalent interactions between EA and the polysaccharide matrix.In vitrofecal fermentation showed that SDs enhanced the production of urolithins, including urolithin M5, urolithin M6, urolithin C, iso-urolithin A and urolithin B, without generating new metabolite types. The EA/FVP 1/3 formulation showed the strongest promotion of urolithin production, with iso-urolithin A reaching 2.36 ± 0.28 μM. 16S rRNA sequencing showed that the enhanced urolithin production was accompanied by shifts in the fecal microbial community. Several bacterial genera positively correlated with urolithin biosynthesis, includingBacteroides_H,Negativicoccus,Parabacteroides_B,Unclassified_EggerthellaceaeandLactococcus_A, were significantly enriched in the SDs groups. These findings suggest that FVP-based SDs may serve as a potential strategy for improving the apparent solubility, aqueous dispersion and microbial biotransformation of EA.