Structure and rheology of the kappa-carrageenan/locust bean gum gels

The structure and interaction Of kappa -carrageenan and locust bean gum (LB G) has been studied using rheology, cryo-SEM, conductivity and syneresis ch aracterization. The rheological behaviour of the binary system has been cha racterized using both compression and shear measurements. Elimination of sl ip in the shear measurements yields G ' values of the order 10,000-30,000 P a for a 1% kappa -carrageenan gel in 0-0.2 M added KCl. These values are hi gher than previously reported. No synergistic peak was found with the addit ion of LBG as has been previously reported. ne measured modulii for these g els yields a Poisson's ratio of 0.5. Compression rupture stress and strain were also monitored. The rupture measurements do show a synergistic peak in dicating that the interaction does occur and is important at high strain am plitudes. The gel points as determined by conductivity for these systems sh ow a decrease in temperature with increasing LBG concentration, which is co nsistent with rheological measurements. Syneresis results are reported for the range Of kappa -carrageenan/LBG ratios. The syneresis shown by the mixt ures is the same as that shown by the same concentration of K-carrageenan. Structures of the gels as determined by cryo-SEM are also reported. Charact eristic length scales in these systems are of the order of tens of microns and show little change with LBG concentration. The reduction in the charact eristic length scale with increasing LBG concentration is discussed in term s of the rheological behaviour. (C) 2001 Elsevier Science Ltd. All rights r eserved.