Molecular interaction between xanthan and locust bean gum in dilute solution

Four studies were carried out to investigate the interaction between xanthan gum and locust bean gum in dilute solution. In the first study, we used an oscillatory capillary rheometer to investigate visco-elastic properties of xanthan and locust bean gum (LBG) blends in dilute solution. Gums were evaluated for intrinsic viscosity and the elastic component. Molecular conformation of the complex of xanthan-LBG was assessed by the power law and the Huggins equations. A 60% xanthan-40% LBG blend exhibited the strongest attraction between xanthan and LBG molecules as evidenced by a greater intrinsic viscosity, the polymer miscibility coefficient alpha, and the elastic component. The power-law coefficient b increased as the LBG fraction increased in the blends, suggesting a more flexible xanthan-LBG complex dependent on LBG. The second study investigated the effects of NaCl, KCl, and CaCl2 on visco-elastic properties of xanthan and LBG blends in dilute solution using an oscillatory capillary rheometer. Addition of any of the three salts significantly reduced the intrinsic viscosity and elastic component of the gum blends, with a pronounced effect from divalent ions, compared to monovalent ions. The 60% xanthan-40% LBG blend exhibited the strongest attraction between xanthan and LBG. For the three salts, the attraction weakened with the addition of 5-mM salt and vanished with the addition of 50-mM salt. With addition of 50 mM of any of the three salts, the coefficient alpha was negative, suggesting a strong repulsion between the two gums. The power-law coefficient b increased as salt concentration and LBG fraction increased in the blends for the three salts, suggesting a more flexible xanthan-LBG complex dependent on salt concentrations and LBG. The third study investigated the interaction between xanthan and LBG in dilute solution using size-exclusion chromatography (SEC) coupled with multiangle laser light scattering (MALLS). Results showed that a synergistic interaction between xanthan and LBG occurred, which was evidenced by an increase in refractive index area for xanthan and a decrease in refractive index area for LBG. In the fourth study, we used the atomic force microscopy (AFM) technique to study the interaction between xanthan and LBG. Results showed xanthan molecules in a rigid rod shape interacting with adjacent and spherical LBG molecules to form the complex xanthan-LBG.