Structural elucidation of mulberry leaf oligosaccharide and its selective promotion of gut microbiota to alleviate type 2 diabetes mellitus

Two oligosaccharide fractions (MLO 2-1 and 2-2) were purified from enzymatic hydrolysate of mulberry leaf polysaccharide. The results of simulated digestion showed that MLO 2-2 was a digestible oligosaccharide, which could be degraded by human digestive juice; while MLO 2-1 possessed the non-digestible property in the upper gastrointestinal tract and performed the function by regulating the gut microbiota. Hence, MLO 2-1 was selected for the further analysis. The structure of MLO 2-1 was elucidated as follow: alpha -T-Glc p -(1 -> 3)- beta -Glc p -(1 -> 5)- alpha -Ara f -(1 -> 5)- alpha -Ara f -1 -> 5)- alpha -Ara f -(1 -> 3)- alpha -(2-OAc)-Glc p -1. The in vitro fecal fermentation results showed that MLO 2-1 could modulate the composition of gut microbiota. Meanwhile, MLO 2-1 was effectively metabolized by fecal bacteria to produce lactate and short chain fatty acids, especially acetate and butyrate. The specific metabolic pathways of MLO 2-1 by gut microbiota were further illuminated. Gut microbiota analysis revealed that MLO 2-1 selectively promoted the growth of Ligilactobacillus murinus , a commensal bacterium presented a reduced level in T2DM mice. Animal experiments indicated that MLO 2-1 and L. murinus exhibited hypoglycemic activities. These results demonstrated that MLO 2-1 might alleviate T2DM by selectively accelerating the proliferation of L. murinus . (c) 2024 Beijing Academy of Food Sciences. Publishing services by Tsinghua University Press. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).