Sol-gel and gel-sol phase transitions Of K-carrageenan in pure water and in KCl solution were studied using photon transmission technique. Photon transmission intensity, I-tr was monitored against temperature to determine the sol-gel and gel-sol temperatures (T-sg and T-gs) and activation energies (DeltaH(sg) and DeltaH(gs)). It was observed that T-gs was notably higher than T-sg due to the hysteresis on the phase transition loops. T-gs and DeltaH(gs) 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 T-gs and T-sg. Similarly DeltaH(sg) 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. (C) 2002 Elsevier Science B.V. All rights reserved.