Rheological properties of rice starch-xanthan gum mixtures

Rheological properties of rice starch-xanthan gum mixtures (5% w/w) at different xanthan gum concentrations (0%, 0.2%, 0.4%, 0.6%, and 0.8% w/w) were evaluated in steady and dynamic shear. The rice starch-xanthan gum mixtures at 25 degrees C showed high shear-thinning flow behavior (n = 0.13-0.24), and consistency index (K) and apparent viscosities (eta(a,100)) increased with the increase in xanthan gum concentration. In the temperature range of 25-70 degrees C, mixtures followed the Arrhenius temperature relationship. Activation energy (1.83-9.89 kJ/mol) decreased and storage (G') and loss (G') moduli increased with the increase in xanthan gum concentration. The dynamic (eta*) and steady shear (eta(a)) viscosities at several xanthan gum concentrations followed the Cox-Merz superposition rule with the application of shift factor (alpha). Magnitudes of shift factor were in the range of 0.307-0.478. During aging at 4 degrees C for 10 h, the values of G' were found to increase rapidly the early stage and attained the plateau region after a few hours. The increase in rate constant (k) in gelation of rice starch-xanthan gum mixtures was a function of xanthan gum concentration. (c) 2005 Elsevier Ltd. All rights reserved.