Steady and Dynamic Shear Rheology of Rice Starch‐Galactomannan Mixtures

Rheological properties of rice starch‐galactomannan mixtures (5%, w/w) at different concentrations (0, 0.2, 0.4, 0.6 and 0.8%, w/w) of guar gum and locust bean gum (LBG) were investigated in steady and dynamic shear. Rice starch‐galactomannan mixtures showed high shear‐thinning flow behaviors with high Casson yield stress. Consistency index ( K ), apparent viscosity (η a,100 ) and yield stress (σ oc ) increased with the increase in gum concentration. Over the temperature range of 20–65°C, the effect of temperature on apparent viscosity (η a,100 ) was described by the Arrhenius equation. The activation energy values ( E a = 4.82–9.48 kJ/mol) of rice starch‐galactomannan mixtures (0.2–0.8% gum concentration) were much lower than that ( E a = 12.8 kJ/mol) of rice starch dispersion with no added gum. E a values of rice starch‐LBG mixtures were lower in comparison to rice starch‐guar gum mixtures. Storage ( G ′) and loss ( G ′′) moduli of rice starch‐galactomannan mixtures increased with the increase in frequency (ω), while complex viscosity (η*) decreased. The magnitudes of G ′ and G ′′ increased with the increase in gum concentration. Dynamic rheological data of ln ( G ′, G ′′) versus ln frequency (ω) of rice starch‐galactomannan mixtures have positive slopes with G ′ greater than G ′′ over most of the frequency range, indicating that their dynamic rheological behavior seems to be a weak gel‐like behavior.