Abstract:Polysaccharides were extracted from Ulva lactuca L. and subsequently modified by sulfation using a chlorosulfonic acid-pyridine （CSA-Pyr） system. The effects of the CSA-Pyr volume ratio，reaction time，and reaction temperature on the sulfation process were investigated，with the degree of substitution （DS） as the evaluation index. Response surface methodology （RSM） based on a Box-Behnken design was employed to optimize the sulfation conditions，and the structural characteristics and biological activities of the polysaccharides before and after sulfation were analyzed. The results demonstrated that sulfate groups were successfully introduced into the polysaccharide structure. The optimal sulfation conditions were determined to be a CSA-Pyr volume ratio of 1∶2.5，a reaction time of4.5 h，and a reaction temperature of63 ℃，under which the DS of the sulfated polysaccharide reached 2.44±0.10. Compared with the native polysaccharide，the sulfated polysaccharide exhibited obviously enhanced scavenging activities against DPPH·，O2-·，and·OH radicals，as well as a markedly improved α-glucosidase inhibitory activity. These findings indicate that sulfation modification can effectively enhance the antioxidant and hypoglycemic-related biological activities of Ulva lactuca polysaccharides.