Studies on kappa-carrageenan locust bean gum mixtures in the presence of sodium chloride and sodium iodide

The solution properties of kappa-carrageenan and kappa-carrageenan/locust bean gum mixtures have been studied by small deformation oscillation measurements and differential scanning calorimetry (DSC) in the presence of sodium chloride and sodium iodide. Both salts induced the kappa-carrageenan to undergo a coil-helix conformational change as noted by an increase in the storage and loss moduli (G', G '') and by an exothermic peak in the DSC cooling curves. The enthalpy Delta Hc-h and temperature of the conformational transition Tc-h were higher in NaI compared to NaCl and Tc-h increased with increasing the concentration of both electrolytes. Gelation was not observed for carrageenan or carrageenan/locust bean gum mixtures in the presence of up to 200 mM NaI. Although carrageenan alone did not gel in the presence of 100 mM NaCl, a weak gel war obtained for a mixture containing 09%/0.1% carrageenan/locust bean gum. Furthermore, the mixture showed hysteresis in both the rheological and DSC cooling and heating curves A strong gel was produced for carrageenan alone in the presence of 200 mM NaCl and the gel strength increased on adding a small proportion of locust bean gum (0.9%/0.1%). (C) 1997 John Wiley & Sons, Inc.