Mixed iota and kappa carrageenan gels in the presence of both calcium and potassium ions

The effect was studied of adding both KCl and CaCl2 on gelation of solutions of iota-carrageenan, kappa-carrageenan and mixtures of both types. The gel temperature (T-g) of iota-car was found to be determined by the CaCl2 concentration and T-g of kappa-car by the KCl concentration. At a given salt concentration, iota-car was stiffest with pure CaCl2, but kappa-car gels and mixed carrageenan gels were stiffer when both KCl and CaCl2 were present. Gelation of kappa-car increased the turbidity of mixed carrageenan gels in the presence of KCl or CaCl2, but when both salts were present it led to a drop of the turbidity. In mixed salt, K+ induces formation of a homogeneous kappa-car network that causes the mixed network to become more homogeneous. Rheological and structural properties of carrageenan gels can be tuned for a given polymer and salt concentration by adding both KCl and CaCl2 to kappa-car/iota-car mixtures.