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

The effects of concentration (4-7% starch, db) and temperature (25-70°C) on the steady and dynamic shear rheological properties of Korean azuki bean starch (ABS) paste were investigated in this study. At 25°C all starch pastes exhibited a pseudoplastic shear-thinning characteristic (n = 0.28-0.41). Consistency index (K) and apparent viscosity ( η_a,50) values increased with increasing starch concentration from 4 to 7%. The dependence of η_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 η_a,50 of the ABS pastes at different temperatures (25-70°C). Storage modulus (G′) and loss modulus (G″) values increased with increasing starch concentration, while tan δ (ratio of G″/G′) values decreased. G′ values were much higher than G″ at all frequency values (ω), 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 (η∗) and apparent viscosity (η;_a) values.