Dynamic rheology of rice starch-galactomannan mixtures in the aging process

The effect of galactomananns (guar gum and locust bean gum) at different concentrations (0, 0.2, 0.4, 0.6 and 0.8%, w/w) on the dynamic rheological properties of aqueous rice starch dispersions (5%, w/w) was investigated by small-deformation oscillatory measurements during aging. Magnitudes of storage (G′) and loss (G″) moduli measured at 4°C before aging increased with the increase in gum concentration in the range of 0.2-0.8%. G′ and G″ values of rice starch-locust bean gum (LBG) mixtures, in general, were higher than those of rice starch-guar gum mixtures. G′ values of rice starchguar gum mixtures as a function of aging time (10 h) at 4°C increased rapidly at initial stage and then reached a plateau region at long aging times. However, G′ values of rice starch-LBG mixtures increased steadily without showing a plateau region. Increasing the guar gum concentration resulted in an increase in plateau values. The rate constant (K) for structure development during aging was described by first-order kinetics. K values in rice starch-guar gum mixtures increased with the increase in guar gum concentration. G′ values of rice starch-galactomannan mixtures after aging were greater than those before aging.