Rheological properties of the gellan/water system

Abstract

Rheological properties of the gellan/water system were investigated. Frequency dispersion curves of dynamic storage and loss moduli (G′ and G″, respectively) for gellan/ water at 5 wt% showed solidlike behavior at low temperatures. The values of G′ and G″ appeared to decrease with increasing time after gelation. The temperature dispersion curve of G′ on heating showed a shoulder in the transition region, while no shoulder was observed on the cooling curve. This indicated that the effect of aging on the rheological properties of the gels becomes larger at low temperatures. At 2 wt%, where the system remains liquid, little effect of aging on the rheological properties was observed. The activation energy of flow was estimated to be 30 kJ/mol for the gellan/water system in the random-coil conformation from the temperature dependence of the zero-shear viscosity. Two types of concentration dependence have been observed for the gellan/water system: one corresponds to the curve for gellan in the random-coil form at high temperatures, and the other is for the curve in the helical conformation at low temperatures. The dependence curves at the intermediate temperatures show the transition behavior. © Springer-Verlag 1999.