Cation effects on sol-gel and gel-sol phase transitions of k-carrageenan-water systems

Sol–gel and gel–sol phase transitions of κ-carrageenan in pure water and in KCl solution were studied using photon transmission technique. Photon transmission intensity, Itr, was monitored against temperature to determine the sol–gel and gel–sol temperatures (Tsg and Tgs) and activation energies (ΔHsg and ΔHgs). It was observed that Tgs was notably higher than Tsg due to the hysteresis on the phase transition loops. Tgs and ΔHgs values were also higher for gels containing KCl than for those without KCl. The increase in carrageenan content caused an increase in both critical temperatures and activation energies for the gels prepared in pure water and in KCl solution. Increases in the KCl/carrageenan ratio, raised both Tgs and Tsg. Similarly ΔHsg was elevated by the increase in cation content of the gel. These results were interpreted as the formation of stronger gels in the presence of KCl in water.