Effect of Different Chemical Modifications on the Antioxidant Activity of Polysaccharides Extracted From <i>Crataegus songarica</i> Fruits

Crataegus songarica fruits polysaccharides (CSP) possess significant antioxidant activity, but the relationship between their chemical modifications and activity is unclear. In this study, five polysaccharide derivatives were prepared by selenide, acetylation, phosphorylation, sulfation, and carboxymethylation modifications. The structural characterization of CSP and its derivatives by multidimensional techniques (HPGPC, GC, UV, FT-IR, Congo red, SEM, XRD, TG, DTG, and DSC). The results showed that the total sugar content, uronic acid content, and molecular weight (Mw) of CSP and its derivatives were reduced, and all of them were heteropolysaccharides composed of rhamnose, arabinose, xylose, mannose, glucose, and galactose in different molar ratios. The structural modifications significantly altered the microscopic morphology, crystalline properties, and thermodynamic properties of CSP and its derivatives. Antioxidant activity studies showed that different modifications had differential effects on polysaccharide activity. Among them, the phosphorylated modified derivatives showed optimal scavenging of DPPH radicals (72.52 ± 0.19%), while the carboxymethylated modified derivatives showed optimal scavenging of ABTS radicals (77.57 ± 0.29%). In the H₂O₂-induced oxidative stress model of HepG2 cells, sulfated modified derivatives decreased the percentage of malondialdehyde (MDA) content by 64.79 ± 0.24%, while carboxymethylated polysaccharides increased the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) by 61.97 ± 0.31% and 52.96 ± 0.33%, respectively, as compared to the model group. The present study confirms that chemical modification can alter the biological activities of polysaccharides and that this series of polysaccharides has potential applications in functional foods and pharmaceuticals.