Abstract: Objective:To investigate the influencing factors of sulfated modification of Bupleurum chinense polysaccharides (BCP), and to elucidate the possible mechanism of improving the antioxidant ability of sulfated BCP (S-BCP). Methods:BCP was sulfated by chlorosulfonic acid-pyridine method. The degree of substitution (DS) of S-BCP was observed by adjusting the volume ratios of chlorosulfonic acid to pyridine(1:2,1:4, and 1:8). The structures of BCP and S-BCP were analyzed by infrared (IR) spectroscopy, the morphology of BCP and S-BCP were observed under scanning electron microscopy (SEM). The antioxidant model was established by using 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging. The experiment was divided into positive control group, BCP group and S-BCP group, and the scavenging rates of DPPH free radical in various groups were compared. Results:When the volume ratio of chlorosulfonic acid to pyridine was 1:4, the reaction time was 2 h and the reaction temperature was 60℃, the maximum sulfur content percentage of S-BCP was 18.62% and the DS was the highest (DS=2.32). Compared with BCP group,the scavenging rate of DPPH free radical of S-BCP was significantly increased (P<0.05). Conclusion:The volume ratio of chlorosulfonic acid to pyridine can affect the DS of S-BCP. The sulfated modification can increase the anti-oxidant capacity of BCP by changing its physic-chemical characters and spatial conformation.

Key words: Bupleurum chinense, polysaccharide, sulfation, anti-oxidant