Rheological behaviour of sesame (Sesamum indicum L.) protein dispersions

Abstract

The rheological parameters, flow behaviour index n, flow consistency index Ki and apparent viscosity η, were estimated for sesame protein dispersions using a rotational rheometer coupled a helical ribbon agitator. The effects of changes in protein concentrations, temperature, ionic strength and pH on the viscosities were investigated. At 20°C, the protein shear viscosity exhibited Newtonian behaviour, and a small increase was found when the protein concentration increased from 2% to 6%. At 40°C, the 4% sesame protein dispersion did not demonstrate Newtonian behaviour, while those at 2% and 6% did. At 60°C, the viscosities for protein concentrations of 2% and 4% followed Newtonian behaviour, while at a concentration of 6% it was non-Newtonian with shear-thickening behaviour. The pH affected protein viscosity, especially at pH 4.0 when the proteins reached their isoelectric point. Protein-NaCl solutions at 0.001, 0.01, and 0.1M NaCl presented a Newtonian behaviour. At greater ionic strength, i.e., 0.5 and 1.0M, the apparent viscosity of the proteins increased, and their behaviour became shear thinning, which was related to the high salt concentration. Rheological properties reported here might be more reliable than those reported with conventional geometries as concentric cylinders.