EFFECT OF ETHANOL ON THE FOAMING OF AQUEOUS PROTEIN SOLUTIONS

The influence of ethanol on the stability of foams formed from dilute aqueous solutions of four proteins (β-casein, lysozyme, β-lactoglobulin and gelatin) has been investigated at pH 7 and 25°C. Results were obtained using a shaking method, which, for solutions containing a volatile solvent, is shown to be preferable to a sparging method. Irrespective of protein type or concentration, we found a sharp increase in foam lifetime with small additions of ethanol, followed by a gradual fall with larger additions. The maximum foam stability occurs at 0.2-0.3 wt% alcohol. Relative stabilities of the foams formed from solutions of the four proteins lie in the order: gelatin ≫ β-casein ≫ β-lactoglobulin ≫ lysozym. © 1990.