Degradation of low-molecular-weight fucoidans by human intestinal microbiota and their regulation effect on intestinal microbiota and metabolites during in vitro fermentation

Fucoidan, a sulfated polysaccharide from brown algae, has been shown to improve gut microbiota balance and function. However, the relationship between molecular weight of fucoidan and colonic fermentation characteristics is still unclear. Here, the interaction between different-molecular-weight fucoidans and intestinal microbiota was analyzed via an in vitro fecal fermentation model. Results showed that fucoidan and its 2 low- molecular-weight derivatives (Dfuc1 and Dfuc2) could be utilized by intestinal microbiota after 48 h of fermentation, and among them, Dfuc2 exhibited the highest utilization efficiency of 30.1%, followed by Dfuc1 (24.5%) and fucoidan (14.4%). Notably, the components glucose, mannose and galactose, but not fucose, in different-molecular-weight fucoidans could be utilized. Moreover, intestinal microbiota could degrade Dfuc1 and Dfuc2 to produce oligosaccharide fragments, such as fucose-hexose disaccharide. In addition, fucoidan, Dfuc1 and Dfuc2 displayed different prebiotic effects on the intestinal microbiota community. Native fucoidan preferred to promote Bacteroides and Lactococcus, and low-molecular-weight fucoidans tended to promote Parabacteroides and Lactobacillus. Furthermore, metabolites analysis showed that fucoidan, Dfuc1 and Dfuc2 had similar promoting effects on acetic acid and propionic acid, and had no effect on butyric acid. But they could regulate carbohydrate metabolic pathways and amino acid pathways to varying degrees and with decreasing molecular weight, more differential metabolites were found. Thus, Dfuc2 with a lower molecular weight has more potential to become a potential prebiotics to improve intestinal health.