ζ potential measurement for air bubbles in protein solutions

Abstract

Protein adsorption at gas–liquid interfaces is important in a number of processes including foam formation in bioreactors, foam fractionation for protein recovery, and production of protein based food and drinks. The physical properties of the gas–liquid interface will influence foam stability; important properties will include both surface rheological and electrokinetic properties. While surface rheological properties of gas–protein solution interfaces have been reported, there are no published values for electrokinetic properties at such interfaces. In this paper, ζ potential values of gas bubbles in solutions of three proteins, measured using a microelectrophoresis technique, are reported. The three proteins chosen were BSA, β-casein, and lysozyme; these proteins have all been used previously in protein foaming studies. The effect of protein concentration and ionic strength is considered. For BSA and β-casein, ζ potential was found to increase with increasing protein concentration and ionic strength. For air bubbles in lysozyme solutions, measured ζ potential was zero. ζ potential values for air bubbles in some binary protein mixtures are also presented.