RHEOLOGICAL BEHAVIOR OF KAPPA-CARRAGEENAN GALACTOMANNAN MIXTURES AT AVERY-LOW LEVEL OF KAPPA-CARRAGEENAN

The rheological behaviour of kappa-carrageenan/galactomannan blends, a t ratios ranging from 1/99 to 5/95 in the presence of KCl, was investi gated by means of viscosity and oscillatory shear measurements. These experiments were performed at 1% total polymer concentration and at 15 C. The results were compared to those of the galactomannans alone (loc ust beam gum or guar gum). The mixtures exhibited gel-like properties provided the KCl content was high enough to induce stabilisation of th e kappa-carrageenan molecules in the helical conformation. This limiti ng KCl content for gelation was of the order of 0.02% and did not depe nd upon the kappa-carrageenan concentration under these experimental c onditions. The mixtures exhibited similar tendencies overall irrespect ive of whether the galactomannan was guar gum or locust beam gum. Howe ver, the phenomena appeared somewhat less pronounced with guar gum tha n with locust bean gum. The results are discussed on the basis of a mo del assuming the formation of a biphasic system, one phase being enric hed with the galactomannan, the other phase consisting of kappa-carrag eenan. Since the galactomannan remains the major component, the proper ties are primarily governed by this polysaccharide in solution. The ge l-like properties of the mixture result from gelation of the kappa-car rageenan, this having a dominating effect upon the rheological behavio ur of the galactomannan.