Abstract: To discuss the difference in monosaccharide composition and antioxidant activity among different algal polysaccharides,we analyzed the Ulva lactuca L.,Laminaria japonica,Undaria pinnatifida Suringar and Porphyra of Beibu Gulf in Guangxi.The monosaccharide compositions were analyzed by HPLC applied to PMP precolumn derivation.The antioxidant activity of polysaccharides was indicated by the scavenging DPPH,hydroxyl (·OH^-),and superoxide anions (O₂^-·) activity from algae polysaccharide.Results indicated that four algal polysaccharides were significantly different in monosaccharide composition by PCA analysis.Ulva lactuca L. and Porphyra were mainly composed by Glucosec,Laminaria japonica and Undaria pinnatifida Suringar was composed by Mannoseand Galactose,respectively.The scavenging capacity of DPPH of Undaria pinnatifida Suringar (the hemi-inhibitory concentration IC₅₀ was 0.56±0.02 mg/mL) was significantly higher than that of Ulva lactuca L.,Laminaria japonica and Porphyra.The scavenging ability for (·OH^-) of Porphyra polysaccharide (IC₅₀ was 26.59±0.98 mg/mL) was significantly lower than that of Ulva lactuca L.,Laminaria japonica,Undaria pinnatifida and Suringar.According to the scavenging superoxide anions (O₂^-·)  activity,Ulva lactuca L. was significantly higher than Undaria pinnatifida Suringar,and the value of IC₅₀ of Ulva lactuca L. and Undaria pinnatifida Suringar were 1.61±0.17 mg/mL and 2.73±0.06 mg/mL,respectively.Besides,Pearson correlation analysis and redundancy analysis both showed that glucose (Glc),ribose (Rib),xylose (Xyl) significantly influenced the antioxidant activity of algae polysaccharide (P<0.01).

Key words: algae, polysaccharide extraction, monosaccharide composition, antioxidant activity