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.