Abstract:Jujube polysaccharide was obtained by water-extraction and alcohol-precipitation method from Ziziphus jujuba cv.Hamidazao and purified by defatting，deproteinization，and dialysis.The purified jujube polysaccharide was respectively modified by carboxymethylation，sulfation，and selenization，and then the structures of modified jujube polysaccharides were characterized.The jujube polysaccharide had a molecular weight of 136 413 Da and the polysaccharide content of 49.96%.The carboxymethylated jujube polysaccharide had the highest yield（91.1%），with the substitution degree of 0.42，the polysaccharide content of 36.51%，and the molecular weight of 46 637 Da.The sulfated jujube polysaccharide had the substitution degree of 1.65，the polysaccharide content of 42.73%，and the molecular weights of 9 970 Da and 6 149 Da.The selenized jujube polysaccharide had the selenium content of（580.15±11.96）μg/g，the polysaccharide content of 44.56%，and the molecular weight of 136 153 Da.The selenized jujube polysaccharide had the highest galacturonic acid content（53.23%）.The content of galacturonic acid in jujube polysaccharide（48.17%）was higher than that in sulfated jujube polysaccharide（30.51%）and carboxymethylated jujube polysaccharide（39.60%）.The infrared spectra showed that the modified polysaccharides still had functional groups of polysaccharides，and the change of other infrared indicators indicated that the modification was successful.