Chemical Modification of <italic>Rosa roxbunghii</italic> Tratt. Polysaccharide and Their Antioxidant and Hypoglycemic Activities

To improve the functional properties of Rosa roxburghii Tratt. polysaccharide (RTFP), this study prepared crude polysaccharides (RTFP-40, RTFP-60) using water extraction, which were then separated, purified, and chemically modified to obtain sulfated polysaccharides (S-RTFP-40, S-RTFP-60) and phosphorylated polysaccharides (P-RTFP-40, P-RTFP-60). The effects of chemical modification on their structure and bioactivity were explored through in vitro antioxidant and hypoglycemic experiments. The results showed that both modifications could significantly alter the triple-helix structure of the RTFP-40 and RTFP-60 extracts and introduce sulfate and phosphate groups into the polysaccharide structure. Both modifications significantly improved the in vitro hypoglycemic ability of Rosa roxburghii polysaccharides, with the GDRI indices of S-RTFP-60 and P-RTFP-60 increasing by 8.27% and 3.73%, respectively. All four derivatives enhanced the inhibitory effect on α-amylase, with S-RTFP-40 and S-RTFP-60 increasing it by 15.19% and 41.53%, respectively. Excessive phosphorylation had a negative effect on antioxidant activity. Comparatively, sulfation was more effective than phosphorylation in enhancing both antioxidant and hypoglycemic activities of the polysaccharides, with S-RTFP-60 showing a notable increase in vitro hypoglycemic activity. In summary, sulfation modification is suitable for improving the hypoglycemic activity of Rosa roxburghii polysaccharides.