The effect of polymer degradation was studied on immunomodulatory and antioxidant properties of fucoidan isolated from S. angustifolium. Partially hydrolyzed fucoidans were prepared using 0.01 N hydrochloric acid after incubation for 10 and 15 min in boiling water. FT-IR analysis showed two major peaks at 850 cm-1 corresponding to bending vibration of C-O-S of sulfate and 1256 cm-1 derived from the stretching vibration of S-O. The native fucoidan consisted mainly of carbohydrate (49.4%), sulfate (22.9%), uronic acid (10.3%) and minor amount of protein (4.1%). The hydrolysis reduced the molecular weight of native fucoidan from 421 × 103 g/mol to 104.1 × 103 g/mol after 10 min boiling and 63.9 × 103 g/mol after 15 min boiling, without a significant change in their chemical compositions. Acid degradation increased the specific volume of gyration from 0.84 to 3.32 cm3/g in hydrolyzed fucoidan polymers. Fucoidan with the lowest molecular weight showed the greatest proliferating effect on RAW264.7 cells and induced the macrophage cells to release more nitric oxide (39.0 μmol) at 50 μg/mL. The DPPH radical scavenging activity, ABTS radical scavenging activity and reducing power remarkably increased after hydrolysis. The current results showed that molecular weight has determinant effect on immunomodulatory and antioxidant activities of unrefined fucoidan and thus acid hydrolysis can be applied on commercial scale to obtain fucoidans with more beneficial effects.
Keywords: Fucoidan; Hydrolysis; Immunomodulatory; Molecular weight; Sargassum angustifolium.