RHEOLOGY AND FRACTURE OF MIXED IOTA-CARRAGEENAN AND KAPPA-CARRAGEENAN GELS - 2-STEP GELATION

It is shown that under certain circumstances, on cooling mixed l- and K-carrageenan solutions, the two forms gel separately at different temperatures, with the l form gelling first. This 'two-step gelation' was only observed when both sodium and potassium ions were present, with a sodium/potassium mole ratio of between 1 and 100. For such mixed gels, a K fraction as low as 2.5% of the total carrageenan has significant effects on their rheology, both at low deformation and fracture. In these systems, the K form, gelling in the presence of an existing l gel, produces measurable rheological effects at much lower concentrations than if it were alone. This behaviour can be used as a sensitive test of the 'rheological purity' of samples of l-carrageenan.