Catabolism of Saccharina japonica polysaccharides and oligosaccharides by human fecal microbiota

Saccharina japonica polysaccharides (SJPs) and S. japonica oligosaccharides (SJOs) produced by mild acid hydrolysis, were used for in vitro fecal fermentation to evaluate their potential nutritional benefits. Changes in fecal microbiota and functional metabolites (short-chain fatty acids, SCFAs) were determined during the fermentation. The fermentation behavior of SJPs and SJOs were characterized using high-performance size-exclusion chromatography coupled with mull-angle laser light scattering, viscometry, and refractive index detector and fluorophore-assisted carbohydrate gel electrophoresis (FACE). The main monosaccharides of SJPs consist of mannose, glucuronic acid, galactose, and fucose. The total SCFAs levels increased significantly, with the relative substrate fermentability of samples at 24 h in the order: SJOs > fructo-oligosaccharides > SJPs > blank control. Moreover, SJPs and SJOs could modulate gut microbiota composition by increasing the relative abundances of phylum Bacteroidetes, while decreasing that of Proteobacteria. The molecular weight, intrinsic viscosity, and radius of gyration of SJPs were all decreased during the fermentation, while the FACE results showed that SJOs were degraded. Overall, S. japonica derived polysaccharides and oligosaccharides have great potential use as prebiotics and functional food products.