Effects of extraction methodologies on structural characterization and gut microbiota fermentation properties of Apocynum venetum polysaccharides.

Apocynum venetum L. polysaccharides are classified into neutral-to-acidic heteropolysaccharides rich in glucuronic acid, exhibiting antioxidant, immunomodulatory, and potential prebiotic activities. Different extraction methods have a significant impact on the structural characterization and biological activity of polysaccharides. This study aims to compare the structural characteristics and in vitro prebiotic activity of the Apocynum venetum L. polysaccharides BAC and CEL-U obtained via Bacillus velezensis fermentation and the combined ultrasonic-cellulase method, respectively. The results showed that BAC and CEL-U were acidic heteropolysaccharides composed of rhamnose, arabinose, galactose, glucose and galacturonic acid, and they all showed linear branching structure. Compared with CEL-U, BAC had lower molecular weight (17.51 kDa), higher uronic acid content (27.27%) and typical triple helix structure. In vitro fermentation showed that BAC can produce more propionic acid and butyric acid, maintain a lower pH, promote the proliferation of beneficial bacteria (Segatella and Prevotella), and inhibit potentially harmful bacteria. Metagenome analysis further revealed that BAC played a prebiotic role by activating specific glycosidase-mediated degradation pathways and enriching functional pathways related to carbohydrate metabolism. These findings clarify the structure-activity relationship of Apocynum venetum polysaccharide and provide a theoretical basis for its targeted application in the field of intestinal health.