Connection between rheological parameters and colloidal interactions of a soy protein suspension

The viscosity of a 9.1% (w/w) aqueous suspension of soy proteins at pH 7.5, which constitutes a colloidal dispersion of negatively charged and hydrated particles, is analyzed in relation to colloidal interactions. An experimental study is carried out through the classical shear rate rheometry, in the range 20-50 degrees C. Viscosity data at different temperatures and shear rates are superimposed onto a master plot, which shows the characteristic shear-thinning behavior of colloidal suspensions. A microstructural model for the low shear limit viscosity is derived to establish a quantitative relationship between the viscosity and the interparticle forces in the suspension. Apart from the electrical forces, the hydration repulsive force must be considered in the calculation of the protein-protein interaction energy, in order to achieve a satisfactory prediction of the high viscosity values obtained experimentally. It is also observed that the relaxation time associated to small shear deformations differs from the characteristic relaxation time of the steady shear flow. The theoretical analysis carried out in this work explains the effect of colloidal interactions on rheological parameters of the soy protein suspension. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.