Rheological properties of aqueous fucoidan solutions

Rheological properties of the solutions of fucoidans- -natural polysacchari des isolated from brown algae collected in various regions of the Far-East Coast of the Pacific Ocean were investigated. A broad spectrum of the subst ances studied allowed variation of the properties of polysaccharides to be followed, depending on the carbohydrate composition ad the degree of sulfat ation. The investigations were performed in the systems of three types: aqu eous solutions, solutions in water-glycerol and water-diol systems, and fuc oidan-albumin mixtures. Dissolution of the polysaccharides in water is acco mpanied by a considerable increase in viscosity, but no gel formation is ob served until the fucoidan concentration reached 25 wt %. Fucoidans with gre ater molecular masses and higher degrees of sulfatation form solutions of h igher viscosity. Adding glycerol and diols also leads to a significant incr ease in viscosity. In the case of high-molecular-mass fucoidans, glycerol a nd 1,4-butanediol induce a sol-gel transition. The effect is explained by p oor quality of the mixed solvent and by crosslinking of the neighboring pol ysaccharide molecules as a result of the hydrogen bond formation. Fucoidans form complexes with albumin, the process being controlled by electrostatic interactions between charged groups of both molecules. It is suggested tha t an increase in the solution viscosity in this system is related to unfold ing of the protein globule caused by electrostatic repulsion of the adsorbe d fucoidan molecules.