Rheological properties of azuki bean starch pastes in steady and dynamic shear

Abstract

The effects of concentration (4-7% starch, db) and temperature (25-70 degrees C) on the steady and dynamic shear rheological properties of Korean azuki bean starch (ABS) paste were investigated in this study. At 25 degrees C all starch pastes exhibited a pseudoplastic shear-thinning characteristic (n=0.28-0.41). Consistency index (K) and apparent viscosity ((a,50)) values increased with increasing starch concentration from 4 to 7%. The dependence of (a,50) on the temperatures followed the Arrhenius equation for all samples, and the activation energy (E-a) values of flow increased with increasing starch concentration from 4 to 6%. Both the power law and exponential models were suitable for relating starch concentration with (a,50) of the ABS pastes at different temperatures (25-70 degrees C). Storage modulus (G) and loss modulus (G) values increased with increasing starch concentration, while tan (ratio of G/G) values decreased. G values were much higher than G at all frequency values (), and were frequency dependent. The Cox-Merz rule is not applicable to the ABS pastes at different starch concentrations, showing that there was a deviation between dynamic viscosity (*) and apparent viscosity ((a)) values.