Rheological and thermal effects of galactomannan addition to acorn starch paste

Effect of galactomannans (guar gum and locust bean gum) at different concentrations on theological and thermal properties of acorn starch pastes was examined. Steady and dynamic shear rheological tests indicated that the magnitudes of consistency index (K), apparent viscosity (eta(a,100)). Casson yield stress (sigma(oc)), dynamic moduli (G`, G ''), and complex viscosity (eta*) of acorn starch-galactomannan mixtures were much higher than those of the control (0 g/100 g gum concentration), and that these values also increased with an increase in gum concentration. At temperatures ranging from 25 to 70 degrees C, the effect of temperature on eta(a,100) was well described by the Arrhenius equation. In addition, DSC studies showed that the presence of galactomannans resulted in an increase in the transition temperatures (T-o, T-p, and T-c) and a decrease of the gelatinization enthalpy (Delta H). In general, these results suggest that the presence of galactomannans in acorn starch modifies the rheological and thermal properties, but that these modifications are dependent on the gum type and gum concentration. (c) 2010 Elsevier Ltd. All rights reserved.