Rheological properties of rice starch–xanthan gum mixtures

Abstract

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 °C showed high shear-thinning flow behavior ( n = 0.13–0.24), and consistency index ( K) and apparent viscosities ( η a,100) increased with the increase in xanthan gum concentration. In the temperature range of 25–70 °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 ( η ∗) and steady shear ( η a) viscosities at several xanthan gum concentrations followed the Cox–Merz superposition rule with the application of shift factor ( α). Magnitudes of shift factor were in the range of 0.307–0.478. During aging at 4 °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.