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In this study, two degraded polysaccharides were obtained by H 2 O 2 -Vc-ultrasonic and H 2 O 2 -Fe2+-ultrasonic treatment from Codium cylindricum. The basic structure of polysaccharides was characterized and the relationship between structure and antioxidant activity was studied. FTIR spectrum indicated that the degraded polysaccharides had similar functional groups (O H, C H, C O group) with ordinary polysaccharides. LC-MS analysis showed that the degraded polysaccharides were composed of the same monosaccharide units (mannose, galactose, arabinose, glucose, ribose) with Codium cylindricum polysaccharides, but the molar ratio was different. Meanwhile, the molecular weight and morphological feature of polysaccharides had been changed after degradation. Additionally, the antioxidant activity assay revealed that two degraded polysaccharides with lower molecular weight possessed better antioxidant property than ordinary polysaccharides. These results suggested that the basic structure of polysaccharides had not been damaged by two degradation methods, while the antioxidant activity was significantly enhanced. [ABSTRACT FROM AUTHOR]

Degradation of sulphated polysaccharides from Grateloupia livida (GLP) was studied using H 2 O 2 -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 H 2 O 2 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. • Grateloupia livida (GLP) polysaccharide were degraded using H 2 O 2 -Vc and microwave. • Optimal conditions were obtained after Box-Behnken response surface analysis. • Two sulfated polysaccharide constituents (DGLP-1 and DGLP-2) were isolated from DGLP. • DGLP-1 and DGLP-2 possess good antioxidant properties. [ABSTRACT FROM AUTHOR]