Structurally orientated rheological and gut microbiota fermentation property of mannans polysaccharides and oligosaccharides

Three mannan polysaccharides and their oligosaccharides were investigated in terms of physicochemical characteristics and effects on gut microbiota. Oligosaccharides from guar gum had the fastest fermentation kinetics for SCFAs generation at the initial stage, while the locust bean of both polymers and oligosaccharides demonstrated the lowest SCFAs through the whole fermentation process. In contrast, konjac gum steadily increased SCFAs and reached its maximum level at 24 h fermentation, indicating its fermentation character may be associated with its rheological properties. Compared to their corresponding polysaccharides, all the oligosaccharides demonstrated a faster fermentation kinetics, followed by an enriched abundance of propionate-producing bacterial Prevotella and a decreased abundance of Megamonas and Collinsella. Meanwhile, oligosaccharides reduced the Firmicutes/Bacteroidota ratio as well as the abundance of Bacteroidetes and Escherichia-Shigella. The fermentation of konjac substrate significantly promoted the abundance of butyrate-producing bacterial Faecalibacterium. In contrast, although the fermentation of locust bean and guar gum substrates benefited Bifidobacterium abundance due to their similar structure and monosaccharides composition, the fermentation of locust bean gum led to greater Bifidobacterium than the others, which may be associated with its higher mannose composition in the molecules. Interestingly, the partial hydrolysis of the three polysaccharides slightly reduced their prebiotic function.