In vitro digestion by saliva, simulated gastric and small intestinal juices and fermentation by human fecal microbiota of sulfated polysaccharides from Gracilaria rubra

[Display omitted] •GRPS was not digested under simulating oral, gastric, small intestine conditions.•GRPS was gradually degraded and utilized by gut microbiota.•GRPS administration could increase SCFAs concentration.•GRPS exhibited a modulatory effect on gut microbial structure. In the present study, the changes of polysaccharides from Gracilaria rubra (GRPS) under simulated oral, gastric and small intestine digestion conditions were firstly investigated. The results indicated that GRPS was not digested under such conditions. Then, the prebiotic property of GRPS was investigated via in vitro fermentation by human gut microbiota in mixed cultures. The results showed that GRPS was gradually degraded and utilized by gut microbiota. With the proceeding of fermentation, pH kept a downward trend and the concentration of short-chain fatty acids increased, especially acetic, propionic and isobutyric acids. Furthermore, GRPS exhibited a modulatory effect on microbial structure by lowering the ratio of Firmicutes/Bacteroidetes and increasing the relative abundances of bacteria that could degrade GRPS to satisfy the growth of gut microbiota. The results suggested that GRPS had the potential to be developed as prebiotics.