Rheological properties of rice starch–xanthan gum mixtures Original Research Article

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 (ηa,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 (ηa) 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.