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 vesiculosus polysaccharide (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 vitro fecal 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, including Bacteroides_H, Negativicoccus, Parabacteroides_B, Unclassified_Eggerthellaceae and Lactococcus_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.