Antioxidant activity of purified fractions obtained from membrane ultrafiltration of hydrolysed fucoidan from brown seaweed Nizamuddinia zanardinii

Polysaccharides are one of the biomacromolecules that, in addition to their peculiar physicochemical properties, possess promising biological capabilities depend on chemical structure. The purpose of the present study was to evaluate the effect of membrane ultrafiltration on antioxidant properties of hydrolysed fucoidan from brown seaweed Nizamuddinia zanardinii. After removing pigments and low molecular weight compounds, the extracted crude fucoidan, was hydrolysed by 0.01N hydrochloric acid at 100°C for 20 minutes (FH20). Then, FH20 was fractionated using ultrafiltration with 2, 10, 30, 100 kDa membranes. The average molecular weight of fractions was 553.7, 39.2, 12.4 and 4.6×103 g/mol in KDa>100, 100-30 KDa, 30-10 KDa and 2-10 KDa, respectively. After separation based on molecular weight, the obtained fractions, compared to FH20, which were significantly capable of inhibiting DPPH free radicals (85.05-37.69%), ABTS radicals (89.65-55.43%) and reduction Fe3+ ions (absorption of 0.72-0.07). In the meantime, 2-10 KDa fraction had the greatest potential in inhibiting DPPH free radicals (85.05-74.12%), ABTS free radicals (89.65-75.16%) and reducing Fe3+ ions (absorption of 0.21-0.72). Overall, the results of this study showed that reducing the molecular weight of fucoidan to a specific range could lead to significant increase of antioxidant activity.