Structural Characteristics and Antioxidant Activities of Fucoidans from Five Brown Seaweeds

Five kinds of fucoidans from the brown seaweeds Cladosiphon okamuranus, Sargassum hornery, Kjellmaniella crassifolia (Saccharine sculpera), Nemacystus decipiens, and Fucus vesiculosus, were isolated according to a previously reported procedure with slight modification. The scavenging activities of DPPH radical, superoxide radical, and hydroxyl radical, as well as the ORAC value were measured for the isolated fucoidans. Fucoidans from S. hornery, F. vesiculosus, and K. crassifolia showed higher antioxidant activity than that from S. hornery and C. okamuranus, except for the hydroxyl radical scavenging activity. The relationship between the antioxidant activity and the structure was examined for each fucoidan. Fucoidans with high amount of sulfate groups did not necessarily result in increased antioxidant activity, although the sulfate group itself was essential for the antioxidant activity. Furthermore, the fucoidan linked to a side chain monosaccharide, such as GlcA, demonstrated similar antioxidant activity. The antioxidant activity of the fucoidans was possibly due to a combination of the factors involved, such as the amount of sulfate groups, the position of the sulfate groups, the kind of side chain sugar, the linkage of a side chain sugar, and the molecular weight.