Study on Carboxymethylation Modification and Antioxidant Activity of Polysaccharides from Zizyphus jujuba

To investigate the changes of structural characteristics and antioxidant activity of carboxymethylated jujube polysaccharides, this study was carried out on the Zizyphus jujuba polysaccharide carboxymethylated modification. The crude polysaccharides of jujube were used as raw materials, deproteinization by Sevage method and decolorization by macroporous resin AB-8, then the polysaccharide was modified by carboxymethylation. With carboxymethyl substitution degree as the index, the concentration of NaOH, the addition amount of monochloroacetic acid and the temperature were optimized by single factor and response surface test. The scavenging ability of DPPH and hydroxyl radical and its reducing power and chelating ability to Fe²⁺ were taken as indexes before and after modification to explore the effect of antioxidant activity of carboxymethylated jujube polysaccharide. The results showed that the optimal process of carboxymethylation modification was as follows: Reaction temperature was 70 ℃, the addition amount of chloroacetic acid was 3.5%, and the concentration of NaOH was 3 mol/L. Under these conditions, carboxymethylated Zizyphus jujuba polysaccharides had the best molecular modification effect, and the degree of substitution up to 1.157. When the concentration was 5 mg/mL, the scavenging rates of DPPH and hydroxyl radical were 93.83% and 44.7%, and the reducing power and chelating capacity of Fe²⁺ were 0.462 and 44.05%. The significant improvement of antioxidant activity of Zizyphus jujuba polysaccharides indicated that carboxymethylation modification could improve antioxidant activity of polysaccharides, which could provide theoretical basis for further study of Zizyphus jujuba polysaccharides.