Comparative assessment of Dendrobium officinale polysaccharides and enzymatically derived oligosaccharides: Structural characterization and in vitro metabolic function modulation and gut microbiota regulation

Metabolic dysregulation is closely linked to impaired glucose metabolism and gut microbiota imbalance, and dietary carbohydrates have emerged as important modulators of these processes. In this study, polysaccharides (DOP) from Dendrobium officinale and their enzymatically derived oligosaccharide fraction (DOO1) were systematically characterized and comparatively evaluated in vitro. Enzymatic hydrolysis markedly reduced molecular weight, increased relative mannose content, and altered glycosidic linkages, yielding DOO1 as a structurally heterogeneous glucomannan-type oligosaccharide. DOO1 mainly consisted of a mannose-rich backbone with →4)-β-D-Manp-(1→ and →4,6)-β-D-Manp-(1→ linkages, along with →4)-β-D-Glcp-(1→ and minor →4)-β-D-2-O-acetyl-Manp-(1→ units. Functionally, DOO1 displayed higher inhibition of α-amylase relative to native DOP and significantly enhanced glucose consumption in palmitic acid treated insulin-resistant HepG2 cells, accompanied by modulation of key metabolic pathways, including arginine biosynthesis, glycerophospholipid metabolism, and the tricarboxylic acid cycle. Resistance to upper gastrointestinal digestion and selective modulation of gut microbial communities were observed in simulated gastrointestinal processing and in vitro fecal fermentation, with a notable increase in the relative abundance of Bacillota and Actinomycetota. Collectively, these findings indicate that enzymatically derived D. officinale oligosaccharides hold considerable promise as functional ingredients for improving metabolic health and supporting gut microbiota balance.