The Critical Role of Molecular Weight in Digestion Stability and Gut Microbiota-Dependent Fermentation of Dendrobium officinale Polysaccharides

This study systematically investigated the impact of molecular weight (Mw) on the gastrointestinal fate and gut microbiota modulation of Dendrobium officinale polysaccharides (DOP). A series of DOPs with different Mw (509-110 kDa) was obtained via ultrasonic degradation. During simulated digestion, all DOPs exhibited partial depolymerization, evidenced by reduced Mw and increased reducing sugar content, with high-Mw DOPs being more susceptible to gastric conditions. Although the triple-helical structure and microtopography were disrupted, the functional groups and biological activity remained largely intact. DOPs were extensively utilized by gut microbiota in an Mw-dependent manner. Notably, low-Mw UDOP-9 preferentially promoted the proliferation of Bacteroides (up to 29.04%) and Parabacteroides, whereas high-Mw DOP selectively enhanced Bifidobacterium growth. All DOPs significantly increased short-chain fatty acid (SCFAs) production, particularly acetate. However, Mw did not affect the total SCFAs content. These findings revealed the important role of Mw in regulating polysaccharide digestion and the gut microbiota.