Comparing the in vitro saliva-gastrointestinal digestion and fecal fermentation of galactomannan fractions with different molecular weights derived from Sesbania cannabina

The molecular characteristics of polysaccharides determine their gastrointestinal behavior and physiological effects. This study aimed to compare the digestion and fermentation profiles of the sesbania gum (SG) galactomannans with different molecular weights (MW), i.e., SG40 (19.9 kDa), SG50 (9.35 kDa) and SG65 (4.73 kDa), using the in vitro models. Based on the MW, reducing sugar, and free monosaccharide results, it could be concluded that all the SG fractions were resistant to hydrolysis during the simulated salivary-gastric-small-intestinal digestion but were consumed by the gut microbiota during the fecal fermentation. The 24-h consumption ratios of SG40, SG50 and SG65 were 74.45%, 68.74%, and 85.34%, respectively. The SG fractions enhanced the production of short-chain fatty acids and decreased the acetic to propionic acid ratio. Simultaneously, the SG fractions, especially SG50 ( p < 0.01), altered the diversity and composition of the gut microbiota by increasing the relative abundance of Bacteroidetes and decreasing that of Firmicutes. Linear discriminant analysis effect size (LEfSe) analysis showed that the SG fractions significantly decreased the relative abundances of 14 taxa belonging to Firmicutes and one taxon belonging to each Bacteroidetes and Synergistetes; whereas, several taxa were increased significantly, including Escherichia_Shigella , Lachnospiraceae_ND3007_group , Faecalibacterium , L. _NK4A136_group and Labrys in SG40, Bacteroides , Parabacteroides and Eubacterium_halliii_group in SG50, and Phascolarctobacterium, Desulfovibrio , Agathobacter , Alistipes , Coprococcus_2 , Bifidobacterium , Dorea , Parasutterella , Clostridium_sensu_stricto_1 , Ruminococcus_1 and Olsenella in SG65. Furthermore, seven metabolic pathways (including Carbohydrate metabolism, Amino acid metabolism, Metabolism of cofactors and vitamins, Lipid metabolism, Metabolism of other amino acids, Glycan biosynthesis and metabolism, and Folding, sorting and degradation) were significantly promoted by SG50 compared to CK. In conclusion, this study reveals the effects of MW on the behavior of SG in the gastrointestinal tract. The data obtained will support the development and application of SG-related functional products from the perspective of their effects on gut microbiota. • SG fractions were all indigestible but fermentable. • SG65 (4.73 kDa) was relatively easier to be metabolized by bacteria. • SG40 (19.9 kDa) and SG50 (9.35 kDa) were more capable of lowering the acetic/propionic acid ratio. • Each SG fraction resulted in different shifts in gut microbiota. • SG50 promoted 7 KOs involved in carbohydrates, lipid, and amino acid metabolisms.