Structural Characterization, Constipation-Relieving, and Hypolipidemic Activity of Polysaccharides from Fresh and Processed Dendrobium officinale

Dendrobium officinale (DO) is a traditional medicinal and edible plant whose polysaccharides help modulate gastrointestinal and metabolic functions. Fresh DO is commonly processed into “Fengdou” to prolong shelf life, but the effects of this processing on polysaccharide structure and bioactivity remain unclear. In this study, polysaccharides from fresh DO (FDOP) and Fengdou (DDOP) were isolated, purified, and comparatively characterized. Fourier transform infrared (FT-IR) analysis indicated similar functional groups and O-acetylated pyranosyl structures in both polysaccharides. Based on monosaccharide composition, methylation, and Nuclear Magnetic Resonance (NMR) analyses, both samples were identified as mannose-glucose heteropolysaccharides. However, FDOP was characterized by a higher mannose-to-glucose ratio (79.77:19.57) and molecular weight (187.1 kDa), as well as a more structurally diversified →4-linked backbone, whereas DDOP contained more glucose (68.74:30.94) and exhibited a lower molecular weight (125.1 kDa) and simplified backbone. In zebrafish models, both polysaccharides were found to alleviate loperamide-induced constipation and reduce lipid accumulation. DDOP showed stronger constipation-relieving activity, whereas FDOP exerted more pronounced hypolipidaemic effects, which may be attributed to its higher molecular weight, mannose enrichment, and more complex backbone structure. These findings provide a structural basis and theoretical support for developing DO-derived polysaccharides as functional food ingredients targeting constipation and dyslipidaemia.