Rheological aspects of the intermolecular interaction between xanthan and locust bean gum in aqueous media.

Non-Newtonianbehavior and dynamic viscoelasticity of a series of aqueous mixed solutions of xanthan and locust bean gumwere measured using a rheogoniometer, and the rheological properties were analysed.A gelation occurred in the mixture at the concentration of 0.2%total gumsat room temperature.The flow curves of the mixture solutions showeda yield value and approximated to plastic behavior at 50°C.The maximumdynamic modulus was obtained whenthe mixing ratio of xanthan to locust bean gum was 1 : 2, while comparable high moduli were also obtained in the mixing ratio of 1 : 3 or 1 : 4. A mixture ofdeacetylated xanthan and locust bean gum showed the highest dynamic modulus, about two times that of the mixture of native or Na-form xanthan.The dynamic modulus of the mixtures decreased rapidly with increasing temperature.In contrast, the dynamic viscosity was scarcely changed during increasing temperature in the mixing ratio of 2: 1.The dynamic modulus was decreased by addition of urea (4.0m), NaCl (0.1%) and MgCl2.Weconcluded that the intermolecular interaction between xanthan and locust bean gum might occur between the side chains of the former and backbone of the latter, as in a lock-and-key effect.