DENSITY, VISCOSITY AND SURFACE TENSION OF WHEY PROTEIN CONCENTRATE SOLUTIONS

We have determined the density, rheological behavior and surface tension of whey protein concentrate (WPC) solutions. Densities (rho) were measured at concentrations of 0.05-0.40 w/w at temperatures of 20-35C. The results were expressed as a function of temperature and mass fraction (w). This function fit the data with deviations of less than +/- 0.4%. Apparent viscosities (eta(a)) for WPC solutions with mass fractions w <= 0.20 at temperatures of 10-40C and high shear rates, 50-1,200/s, were found to be independent of shear rates, implying that the rheological behavior of WPC solutions is Newtonian. Dynamic viscosity (eta) data were fitted to an empirical function of the WPC mass fraction and temperature with a mean deviation of +/- 4.7%. Surface tensions (sigma) were determined for mass fractions between 0.01 and 0.30 at 25C. At this temperature and w = 0.05, there was a critical surface tension, sigma(c) = 42.5 mN/m. When w >= 0.10, the arithmetic mean of sigma at 25C was 46.3 mN/m. The surface tension values were similar to those published for skimmed milk at 25C. In addition, for w = 0.05 and w = 0.20, we found that at temperatures between 20 and 40C, the surface tension decreased linearly with temperature. These linear equations fit our experimental data with an average deviation lower than +/- 0.4%.