Stability and mechanical strength of aqueous foams containing food proteins

Abstract

The role of proteins in the formation and stabilization of foams is important in many food applications. Most such products are made with egg white or milk proteins as emulsifiers. This study is concerned with the foaming properties of high-quality caseins and ovalbumin, as model food systems. The foaming properties (foam strength and stability) were evaluated in an aeration column (bubbling method). Foams were generated with several well-known food proteins: casein, acid casein, sodium caseinate, calcium caseinate, and ovalbumin. Experimental conditions varied as follows: (a) temperature between 5 and 40°C; (b) protein concentration from 0.01 to 1% (w/w); (c) pH between 2 and 9; and (d) ethanol and sucrose were added to distilled water to produce solutions of concentrations between 0 and 1 M. A second-order kinetics model is a satisfactory mathematical description of the foam drainage behaviour, so the discussion of the results is based on the second-order rate constant for drainage. It was observed that intrinsic molecular properties (the nature and extent of protein-protein interactions), as well as environmental and processing factors (temperature, pH and viscosity of the continuous phase) affected the foaming properties. Moreover, foams with enhanced mechanical strength (greater protein-protein interactions) were more stable.