Fermented Sargassum hemiphyllum soluble dietary fiber exhibits enhanced bioactivity and gut microbiota regulation potential in C57BL/6 mice

Sargassum, a sustainable marine resource in China, has less explored soluble dietary fiber (SDF) functions and gut microbiota effects. In this study, SDF was extracted through fermentation with three lactic acid bacteria (LAB) strains, Lactobacillus brevis, Bifidobacterium longum, and Streptococcus thermophilus. Fermentation significantly increased SDF yield to 0.22–0.25 g/g, reduced molecular weight to 27.5–54.8 kDa, and enhanced its water-holding capacity and sodium cholate adsorption capacity. Among the three LAB strains, B. longum (BL-SDF) demonstrated the greatest antioxidant improvement, increasing total phenolic content by 42.8 % and reducing IC50 value for DPPH and hydroxyl radicals by 42.36 % and 48.54 %, respectively (p < 0.05). In vivo studies in C57BL/6 mice using 16S rRNA sequencing revealed that BL-SDF significantly enriched the abundance of beneficial species such as Blautia, Roseburia, Parabacteroides, Alistipes, and Muribaculum. These results provide novel evidence that SDF from Sargassum, especially BL-SDF, could be used as a functional ingredient to improve antioxidant properties and promote gut health.