Structural Characterization of Dendrobium officinale Polysaccharides and Their Regulation Effect on Intestinal Microbiota During In Vitro Fermentation

Polysaccharides derived from Dendrobium officinale have been demonstrated to exhibit metabolic regulatory properties. However, the correlation between their structure and function, particularly their mechanism of action through gut microbiota, remains underexplored. This study systematically elucidates the structural characteristics of Dendrobium officinale polysaccharide (DOP) from the Guizhou (GZ) and Zhejiang (ZJ) provinces of China using nuclear magnetic resonance (NMR) and a series of chromatographic analyses, revealing their unique molecular features. Additionally, the metabolic regulatory activities were assessed through α-glucosidase inhibitory assay and in vitro intestinal flora activity assay. The findings include the following: (1) both DOP-GZ and DOP-ZJ predominantly consist of glycosidic linkages of β-1,4-Manp and β-1,4-Glcp; (2) zhe monosaccharide composition ratios of mannose to glucose are 2.51:1 for DOP-GZ and 2.66:1 for DOP-ZJ, with molecular weights of 356 kDa and 544 kDa, respectively, indicating significant structural differences between DOPs from different sources; (3) treatment with DOP-GZ and DOP-ZJ led to alterations in the α-diversity indices and Firmicutes-to-Bacteroidota ratios; (4) more importantly, DOP-GZ and DOP-ZJ significantly increase the abundance of beneficial bacteria (e.g., g_Proteobacteria_unclassified) while suppressing the growth of pathogenic bacteria (e.g., f_Enterobacteriaceae_unclassified), with statistically significant results. These findings not only uncover a novel mechanism by which DOPs regulate metabolism through gut microbiota but also provide a crucial theoretical basis for the application of DOPs in functional foods and pharmaceutical development.