Subcritical water extraction as an efficient technique to isolate biologically-active fucoidans from Nizamuddinia zanardinii

A sulfated polysaccharide (fucoidan) has been isolated from Nizamuddinia zanardinii using subcritical water extraction method (SCWE), and extraction conditions were optimised using the response surface methodology. The optimum extraction conditions were found to be: extraction time of 29 min, extraction temperature of 150 °C, and raw material-to-water ratio of 21 g/mL. The fucoidan yield under these optimum conditions was 25.98%, which was considerably higher than that of conventional solvent extraction (5.2%). Extraction time and temperature were the extraction variables that most significantly affected fucoidan yield. Chemical and monosaccharide composition, molecular weight, and the antioxidant, anticancer and immunomodulatory activities of the extract have also been investigated. The monosaccharide composition of fucoidan included fucose (34.13%), mannose (30.70%), galactose (23.19%), xylose (9.35%) and glucose (2.65%). The average molecular weight of the extracted fucoidan was 694 kDa. Antioxidant results revealed that SCWE-extracted fucoidan had appreciable ABTS radical scavenging (70.35%) and reducing power (0.182 Abs). The anticancer activity of fucoidan ranged from 24.60 to 49.46% for HeLa cells and from 23.95 to 46.78% for HepG