Variation of the viscosity of a concentrated, sterically stabilized, colloid: Effect of ethanol on casein micelles of bovine milk

Abstract

The relative viscosities of concentrated skimmed milk with and without added ethanol were measured using controlled stress rheometry and Ostwald viscometers. The dependence of relative viscosity on casein micelle volume fraction was found to follow the equation of I. M. Krieger and T. J. Dougherty ( Trans. Soc. Rheol. 3, 137 (1959); Adv. Colloid Interface Sci. 3, 111 (1972)). The addition of ethanol at concentrations below that required for coagulation was shown to cause a reduction in micellar voluminosity. The corresponding reduction in micelle radius is consistent with the reduction in hydrodynamic radius measured by quasi-elastic light scattering. Our experiments validate the use of viscosity measurements on highly concentrated micellar suspensions as a sensitive technique for quantifying small changes in micelle size.