EFFECTS OF SMALL AMOUNTS OF KAPPA-CARRAGEENAN ON THE RHEOLOGY OF AQUEOUS IOTA-CARRAGEENAN

The temperature dependence of the rheology (shear storage and loss moduli) of two ion forms (sodium and potassium) of aqueous iota-carrageenan was investigated in the presence and in the absence of small fractions (less-than-or-equal-to 10%) of added kappa-carrageenan. Both native iota-carrageenan (which already contains kappa-carrageenan as an impurity) and a sample purified by kappa-carrageenase was investigated. In either ion form, pure iota-carrageenan forms a weak gel as a consequence of its conformational transition, and the gel becomes stronger as the helical content increases. No marked ion specificity is seen in the rheology of pure iota-carrageenan. Small fractions of kappa-carrageenan, whether added or present as impurities, have no effect on the rheology of the sodium form but a large effect on the modulus of the potassium form of iota-carrageenan. The storage moduli of the potassium iota/kappa gels fall within the limits expected for a phase-separated gel structure.