Infrared characterisation, monosaccharide profile and antioxidant activity of chemical fractionated polysaccharides from the edible seaweed sugar Kombu (Saccharina latissima)

The central goal of this study was to evaluate the antioxidant activities related to the nondigestible polysaccharides present in the brown alga Saccharina latissima. For this purpose, a chemical fractionation procedure based on the different solubilities of polysaccharides was achieved. FTIR spectra of freeze-dried polysaccharide fractions were recorded to confirm the presence of sulphate. A significant correlation was found between sulphate content in the different fractions tested and antioxidant activities, either by reduction power (RP) or radical scavenging assay (RSA) (RP, P<0.0001; and RSA-ABTS P<0.0001). The acidic fraction, with the highest sulphate content among soluble fractions and presumably containing sulphated fucans, showed the highest antioxidant activity either for reducing power or scavenging assays. Consistently, it is reported that the acid-soluble fraction containing fucans shows higher antioxidant activity than those containing alginate and laminaran in Turbinaria conoides seaweed.