Effect of alcohol on adsorption of casein at the oil-water interface

We report on the effect of added ethanol on time-dependent interfacial tensions and surface shear viscosities at 25 degrees C for adsorbed films of sodium caseinate at the interface between n-hexadecane and an aqueous solution (pH 7. ionic strength 0.005 M) containing from 10 (4) wt% to 10 (1) wt% protein. Addition of 10 wt% ethanol causes changes in interfacial tension which vary from similar to 15 mN/m at short times to just 2-3 mN/m under steady-state conditions. The presence of 1 wt% ethanol inhibits the form at ion of a film with measurable sur face viscosity. Experiments in which ethanol is added to the sub-phase be low an aged protein film arc explained in terms of a rapid displacement step. followed by slow accumulation of ethanol-aggregated protein in secondary layers if the bulk protein concentration is high enough.