Acetylated glucomanno-oligosaccharides from human gut microbial degradation of Dendrobium polysaccharides: production and effects on anti-hyperglycemia-related factors

Dysbiosis of gut microbiota is tight related to metabolic diseases, and are affected by several factors, and the indigestible carbohydrates from food and herbal medicine that are predominantly metabolized and utilized by gut microbes are thought to play key roles. Dendrobium is a noble traditional Chinese herb medicine rich in glucomannan with bioactivities such as regulating blood sugar. Dendrobium Taiseed Tosnobile (DTT) is a potential Dendrobium variety. In vivo studies suggested that the polysaccharides of DTT (DTT_PS) demonstrated significant activities in regulating hyperglycemia-related physiological conditions and increased the abundance of probiotics. Via chemical and spectroscopic strategies, the main polysaccharide of DTT_PS was confirmed to be a partially acetylated glucomannan with a Mn of 194 kDa. To verify whether the indigestible carbohydrates of the DTT_PS regulate blood glucose level, a glucomannan-degrading microbe (Bacteroides ovatus) was chosen to ferment DTT_PS. DTT_PSF2, an acetylated glucomanno-oligosaccharide-rich fraction with a MW range of 0.5–2 kDa, was successfully obtained. The molecular docking results suggested the acetyl substituents of DTT_PS effectively hinder the binding with BoGmuGs (endo-1,4-β-mannosidases of B. ovatus), thereby limiting the degradation. These oligosaccharides exhibited potent activities in promoting GLP-1 accumulation. These findings revealed its potential role of DTT_PSF2 in regulating hyperglycemia.