Structural characterization of a distinct neutral polysaccharide fraction (SP0-1) from sea buckthorn (Hippophae rhamnoides L.) and its antioxidant-related intestinal protection in Drosophila melanogaster.

SP0-1, a neutral polysaccharide fraction isolated from sea buckthorn berries (Hippophae rhamnoides L.), was purified and structurally characterized, and its antioxidant-related intestinal protective effects were evaluated in Drosophila melanogaster. HPGPC analysis showed a single symmetrical peak and indicated a relatively homogeneous fraction with a moderate molecular weight (Mw, 5.59 × 104 Da; ≈55.9 kDa). PMP-HPLC analysis revealed that SP0-1 was mainly composed of galactose, xylose, and arabinose (Gal/Xyl/Ara-rich; Gal:Xyl:Ara = 1:0.38:0.93). Methylation analysis combined with 1D/2D NMR spectroscopy supported the presence of major →4)- and →4,6)-linked Galp motifs, →5)- and →3,5)-linked Araf motifs, and terminal Xylp residues. The consecutive Gal-Gal arrangement, the residue adjacent to Gal O-6, the overall connection of the Ara/Xyl-containing region to the Gal-containing region, and the O-3 substituent of residue D remain unresolved. Functionally, SP0-1 exhibited concentration-dependent radical-scavenging activities against DPPH, ABTS•+, and hydroxyl radicals in vitro. In a Drosophila oxidative-stress model, dietary SP0-1 supplementation significantly improved survival and climbing performance, enhanced endogenous antioxidant enzyme activities, and reduced malondialdehyde levels. Moreover, SP0-1 markedly alleviated H2O2-induced intestinal oxidative injury, as evidenced by decreased reactive oxygen species accumulation and reduced intestinal epithelial cell death. These findings suggest that the structural characteristics of SP0-1, including its proposed Gal-rich linkage features and Ara/Xyl-containing residue motifs, may be associated with the observed antioxidant-related intestinal protection. Collectively, this study provides a structural and functional basis for further investigation of SP0-1 as a potential bioactive polysaccharide fraction.