Zeta potential of sodium caseinate in water-ethanol solutions

The zeta (zeta) potential at pH 7.0 is -42, -10 or -15 mV for an industrial sodium caseinate dissolved in water, in 50% or in 70% ethanol, respectively. The casein solubility as a function of the zeta potential can be represented by an equation describing the ionisation process. The half solubility is at zeta = -13 mV and within 2.3 mV from the inflection point the protein solubility changes from 50 to 90% or to 10%. The electrostatic surface potential is -101 mV in water and it increases to -155 mV in 70% ethanol. The nominal thickness of the electric double layer decreases from 3.5 nm for water solution to 2.9 nm for the 70% ethanol. The distance (d(zeta)) between the surface of shear and the surface of casein aggregate is 3.1, 7.8 and 6.7 nm, respectively, for water, 50 or 70% ethanol. The d(zeta) mainly depends on the viscosity of the solvent.