Flow property of globulin from red bean (Phaseolus angularis)

Abstract

Red bean globulin (RBG) dispersions exhibited pseudoplastic behavior, and the flow data were fitted to the power-law model. With increasing protein concentration, there were progressive increases in consistency coefficient (m), apparent viscosity and yield stress, suggesting protein-protein interactions. The flow behavior index (n) was decreased indicating enhanced pseudoplasticity. Ionic strength affected the flow behavior of RBG, with a reversal in its effect at a specific salt concentration (0.5-1.0 M). Addition of chaotropic salts and protein structure perturbants (urea, sodium dodecyl sulfate and dithiothreitol) caused changes in flow behavior, probably due to dissociation of the oligomers and protein unfolding. Pre-heat treatments at a temperature of 80°C, above the onset temperature of RBG, caused dramatic decreases in n and increases in m and apparent viscosity suggesting protein denaturation/aggregation. When RBG dispersions were heated from 25 to 90°C at a fixed rate (1.7°C/min), there was an initial decrease in apparent viscosity, probably due to a lowering of medium viscosity. The viscosity started to increase at around 78°C, the onset temperature of RBG; and sharp increases were observed from 80 to 90°C. Changes in apparent viscosity with increasing temperature (25-60°C) obeyed the Arrhenius law, with similar Ea values at three different shear rate values, suggesting little temperature dependence of viscosity at lower temperature range. © 2001 Elsevier Science Ltd.