Degradation of sulphated polysaccharides from Grateloupia livida and antioxidant activity of the degraded components.

Degradation of sulphated polysaccharides from Grateloupia livida (GLP) was studied using H2O2-Vc combined with microwave treatment. Optimal conditions were determined after the Box-Behnken response surface analysis. The best degradation conditions were as follows: microwave power 250 W, microwave temperature 54 °C, the concentration of H2O2 3 mM, degradation time 33 min. Under these conditions, the DPPH scavenging activity of the degraded GLP (DGLP) was 71.39 ± 0.17% at a concentration of 6.0 mg/mL. The degradation method is fast and effective, which is beneficial to improve the antioxidant activity of polysaccharides. Two sulphated polysaccharide constituents (DGLP-1 and DGLP-2) were isolated from DGLP and characterized, and their antioxidant activities were determined. The two polysaccharides had high sulphate content (sulphate content: 25.18-25.26%), contained galactose as the major monosaccharide, and had molecular weights of 158.49 ± 0.43 and 18.06 ± 0.92 kDa, respectively. Antioxidant assays suggested that DGLP-1 and especially DGLP-2 possessed good antioxidant properties.