Rheological behaviour of mixed gels of κ-carrageenan-locust bean gum

Abstract

Mixed gels of the K, Na and Ca-forms of κ-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-κ-carrageenan in ≤0·1 m KCl. The composition favouring maximum synergy shifted from 90%-κ-carrageenan in distilled water down to 35% K-κ-carrageenan in 0·1 m KCl. Gels of K-κ-carrageenan/locust bean gum did not show synergistic effects at high potassium concentration (0·2 m KCl). The typical behaviour of K-κ-carrageenan at ≥50 m m 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 m m KCl, and high, 50–100 m m KCl, concentrations because of differences in the potassium-induced microstructure. The mixed gels with the Na or Ca-form of κ-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).