Structural Characterization and In Vitro Fermentation Properties of Polysaccharides from Dragon Fruit (Hylocereus undatus)

Dragon fruit offers numerous health benefits and is widely consumed. However, research on its polysaccharides, crucial constituents of the fruit, remains limited. The study aimed to characterize the structural and biological properties of SDFP-2, a polysaccharide isolated from dragon fruit. Structural analyses revealed that SDFP-2, with a molecular mass of 8.08 × 10⁴ Da, consisted of mannose, glucosamine hydrochloride, rhamnose, glucuronic acid, galacturonic acid, glucose, galactose, and arabinose in a molar ratio of 0.181:0.250:16.544:12.762:3.793:0.739:51.014:14.716. SDFP-2 comprises HG-type and RG-I-type pectic structures, along with an arabinogalactan structure characterized by a main chain of →6)-β-D-Galp-(1→6)-β-D-Galp-(1→, with side chains attached at the O-3 position of the 1,6-β-galactose residues. Functionally, SDFP-2 exhibited notable hypolipidemic and hypoglycemic properties in HepG2 cell assays, significantly reducing lipid accumulation and enhancing glucose metabolism by restoring key glycolytic enzyme activities. In vitro fermentation with fecal microbiota demonstrated SDFP-2's ability to modulate gut microbial composition, elevating beneficial short-chain fatty acid production, including acetate, propionate, and butyrate. This microbial shift favored SCFA producers, such as Coprococcus eutactus and Roseburia intestinalis, while diminishing pro-inflammatory bacteria like Escherichia-Shigella, underscoring SDFP-2's prebiotic potential. These findings elucidated SDFP-2 as a promising dietary intervention for metabolic regulation and intestinal health enhancement.