Evaluation of stepwise precipitation of fucoidan from brown seaweed Nizamuddinia zanardinii on its chemical, molecular and antioxidant properties

The aim of the current study was the evaluation of stepwise recovery of fucoidan extracted from seaweed Nizamuddinia zanardinii and the assessment of relationship between sulfate content and molecular weight with its antioxidant activity. After the removal of pigments and low molecular weight compounds, fucoidan extracted with water was precipitated using different concentrations of ethanol at three levels (30, 50 and 70%). Three fractions of Fuc30, Fuc50 and Fuc70 showed molecular weights of 731.62, 655.76 and 10.41 × 103 g/mol, respectively. The content of sulfate esters in the obtained fractions were measured between 6.49-25.03%. The color evaluation of produced fucoidans by a digital chroma meter indicated the highest lightness index for Fuc50 fraction. Antioxidant results were varying in DPPH radical (43.93-89.40%) and ABTS radical (25.05-96.10%) scavenging activities as well as Fe3+ reducing power (Abs of 0.142-0.259). Overall, the findings of the present study indicated that stepwise precipitation of fucoidan from N. zanardinii leads to production of fractions with different chemical and molecular weight characteristics and antioxidant activities. Besides, although all isolated fucoidan fractions are introduced as potent antioxidant compounds, polymers possessing lower molecular weight and greater sulfate content exert higher antioxidant activities.