Adsorbed surface films of egg albumin

Abstract

The surface tension of egg albumin solutions in 1 M Na 2SO 4 as a function of time yields an inverse S-shaped curve, the maximum rate of change occurring at a film pressure of about 4 dyn/cm. The log of the surface tension after longer times is linear with respect to time and the apparent first order constants for surface tension decay decreased with increasing protein concentration reaching a constant level at about 0.02% protein. The plot of the 20-min film pressures as a function of protein concentration yields a 2-step curve. The first step, at lower protein concentrations, gives a plateau at about 12 dyn/cm followed by an increase in film pressure with protein concentration reaching a second plateau at about 25 dyn/cm and at about 0.02% protein, the film pressure-protein concentration curve is readily reversible with respect to decreasing protein concentration but not so easily reversible with respect to increasing protein concentration. The rates of desorption of protein from solution films transferred to clean ammonium sulfate solution is proportional to the amount of protein in the film minus 1.80 mg/m 2. It is concluded that 1.80 mg/m 2 of protein is irreversibly adsorbed and likely surface denatured. The interpolation of the film pressure-protein concentration curve permits the plot of a force-area curve for the adsorbed film of egg albumin; the adsorbed film is significantly more compressed than is the corresponding spread film.