RHEOLOGICAL BEHAVIOR OF MIXED GELS OF KAPPA-CARRAGEENAN LOCUST BEAN GUM

Mixed gels of the K, Na and Ca-formS Of kappa-carrageenan and locust bean gum at a total polysaccharide concentration of 1% (w/w) were studied by dynamic viscoelastic measurements. Synergistic effects were only observed for mixed gels with K-kappa-carrageenan in less-than-or-equal-to 0.1 M KCl. The composition favouring maximum synergy shifted from 90%-kappa-carrageenan in distilled water down to 35% K-kappa-carrageenan in 0.1 M KCl. Gels of K-kappa-carrageenan/locust bean gum did not show synergistic effects at high potassium concentration (0.2 M KCl). The typical behaviour of K-kappa-carrageenan at greater-than-or-equal-to 50 mm KCl dominated the rheological behaviour of the mixed systems even when the locust bean gum content was high. The synergistic effects probably originate from different mechanisms at low, 0-10 mm KCl, and high, 50-100 mM KCl, concentrations because of differences in the potassium-induced microstructure. The mixed gels with the Na or Ca-form Of kappa-carrageenan showed no synergy. Addition of locust bean gum caused the storage modulus to decrease and the phase angle to increase. The gels were weak, with G' < 170 Pa for the Na form and G' < 350 Pa for the Ca form. The mixed gels with both the Na and Ca forms had a broken frequency dependence of G'(f).