Abstract: DEAE-Sepharose CL-6B column chromatography was used to separate and purify a polysaccharide STP-I from the algae Sargassum thunbergii.The structural assignment of STP-I was performed using Fourier transform infrared spectroscopy (FTIR) analysis,periodate oxidation-smith degradation,methylation analysis and nuclear magnetic resonance (NMR).The repeating unit of STP-I was therefore determined.Major sugar residues of STP-I were6-β-D-Glcp and4-α-D-Galp, other residues including 5-α-L-Araf, 2,3-α-D-Xylp, T-β-D-Xylp and T-β-D-Glcp.The degree of branching (DB) of STP-I was 26.7%.On the basis of radical assays,STP-I exhibited higher scavenging activities of hydroxyl and superoxide radicals than Vitamin C with EC₅₀ values of 0.15 and 1 mg/mL,respectively.STP-I also exhibited the capability of anti-proliferation in human colon cancer cells Caco-2 with IC₅₀ value of 2.56 mg/mL,and cause little loss to common cells.

Key words: Sargassum thunbergii, structural analysis, antioxidant activity, anti-proliferation capability