This study was to investigate the structure and rat fecal microbial fermentation properties of a polysaccharide fraction (PHP2) isolated from the red marine alga Porphyra haitanensis. PHP2 was characterized as a sulfated glucogalactan, with a hypothetical backbone structure of →4)Gα(1→6)G4Sβ(1→4)Glc(1→ and a side chain of Man(1→6)Glc. PHP2 had an irregular spherical chain conformation. The 16S rRNA sequence analysis revealed that PHP2 modulated the rat fecal micro-flora composition, with a similar effect to inulin, changing the dominant genus (Lactobacillus and Escherichia-Shigella) and promoting the growth of organisms that degrade sulfur-containing polysaccharides, such as Desulfovibrio, Ruminococcaceae_UCG-005, and Ruminococcus_2. PHP2 can promote production of acetic, propionic and butyric acid by rat fecal micro-flora. Prediction of metabolic function suggested that PHP2 could modulate cholesterol metabolism. The sulfated glucogalactan fermentation behavior may be associated with its monosaccharide composition, chain branching and chain conformation. PHP2 appeared to have considerable potential as functional food, and was associated with sulfur-containing polysaccharides in general.

Fortunella margarita polysaccharides (FMPS) are composed of 4 polysaccharide fragments, namely mannogalactoglucan, galactoglucan, glucan and arabinoglucan. This study investigated the in vitro fermentation of FMPS fractions and their effect on the fecal microbiota of mice and short chain fatty acids (SCFAs) production. The results showed that the structure of the fecal microbiota was changed after FMPS fermentation. At the phylum level, the polysaccharide fractions reduced the relative abundance of Bacteroidetes compared with the inulin group. At the genus level, the polysaccharide fractions increased the abundance of Lactobacillus, and decreased the abundance of Granulicatella, Proteus and Rummeliibacillus. Polysaccharide fractions could promote the proliferation of beneficial bacteria (Lactobacillus), and decreased harmful bacteria (Granulicatella, Proteus, Rummeliibacillus and Serratia). Furthermore, there was a significant distinction in the genus level flora processed by different polysaccharide fractions, especially mannogalactoglucan. Polysaccharide fractions showed potential prebiotic effects, with mannogalactoglucan, in particular, promoting proliferation of SCFA-producing bacteria. SCFAs were regulated by monosaccharide composition, molecular weight of the FMPS fractions, and the composition of the fecal bacteria. Polysaccharide fractions could modulate metabolic function of the fecal microbiota, altering the levels of SCFAs. These results suggested that FMPS are important functional components in gut health, especially mannogalactoglucan.