Degradation of Laminaria japonica fucoidan by hydrogen peroxide and antioxidant activities of the degradation products of different molecular weights

Conditions of fucoidan degradation by hydrogen peroxide and the antioxidant activities of fucoidans with different molecular weights (Mws) were studied. Fucoidan degradation was monitored by gel permeation chromatography (GPC). Results showed that higher reaction temperature, hydrogen peroxide concentration and reaction time were the main factors that determined the decrease in Mw. There were no significant chemical changes in the backbones of the fucoidans treated with hydrogen peroxide, and the sulphate group contents barely change as compared to the raw polysaccharide. The antioxidant activities of seven fucoidans with different Mws (1.0 kDa, 3.8 kDa, 8.3 kDa, 13.2 kDa, 35.5 kDa, 64.3 kDa, 144.5 kDa) were assessed. The results showed that the relationship between Mws of fucoidans and their antioxidant activities is not simply linear. The samples with Mws of 3.8 kDa, 1.0 kDa and >8.3 kDa have better hydroxyl radical scavenging activity, reducing power and superoxide anion scavenging activity, respectively.