Viscoelasticity, conformational transition and ultrastructure of Kappa-Carrageenan in the presence of potassium ion around the critical total ion concentration

Rheology, microDSC, and confocal laser scanning microscopy were used to study the effect of potassium ion on the viscoelastic behavior, disorder-order transition and the ultrastructure, respectively, of kappa-carrageenan in aqueous medium in the vicinity of the critical total ionic concentration (C*). The rheological tests showed a "weak" gel behavior, with G′>G″ and both moduli dependent on frequency. However, during heating, microDSC showed two zones: one attributed to the presence of ordered double helices without aggregation, and another to the fusion of aggregated double helices. Microscopy showed a three-dimensional network whose continuity depends of the concentration of added potassium ions. For a gel to be formed, a sufficient amount of potassium ion is necessary to promote complete aggregation of double helices so they can form a continuous three-dimensional network.