Influence of alkali treatment and ultrasonication on the bioactivities and rheological properties of sulfated polysaccharides.

The rheological, antioxidant and anticoagulant properties of 17 different structurally uniform and hybrid sulfated polysaccharides are presented in this study. Alkali treatment was used to modify carrageenan precursors, while ultrasonication was employed to partially depolymerize polysaccharide chains. Native and modified sulfated polysaccharides with well-resolved molecular structures were characterized by size exclusion chromatography and dynamic rheometry methods. Extensive ultrasonication (1-64 min) reduced the molecular weights of the samples from approximately 384-1156 kDa to 47-95 kDa. Their rheological properties showed strong dependence on molecular weight, with gelling ability decreasing in the order: furcellaran, kappa carrageenan > iota carrageenan, funoran > lambda carrageenan > theta carrageenan, sulfated chitosan. The anticoagulant activity, measured via aPTT assay, followed the order: lambda carrageenan > iota carrageenan, kappa/iota carrageenan, carrageenan mixture, sulfated chitosan > theta carrageenan > kappa carrageenan, funoran. Among the antioxidant properties determined using Folin-Ciocalteu, DPPH, ABTS, OH radical, and FRAP assays, OH radical scavenging activity was particularly noteworthy, being inherent to all polysaccharides and displaying a correlation with molecular weight. These results validate the interdependence of alkali treatment and the molecular weights of both natural and chemically sulfated polysaccharides in influencing their respective anticoagulant and antioxidant activities measured using in-vitro assays.