Food Chemistry and Fish in Nutrition ( 2+1)

7.3.4. Foam formation and foam stabilization by proteins

Proteins function as foam forming and foam stabilizing components, for example in baked goods, sweets, desert and beer. Foams are dispersions of gases in liquids. Proteins stabilize by forming feasible, cohesive foam around the gas bubbles. During impact, the protein is adsorbed at the surface via hydrophobic areas. There is partial infolding (surface denaturation). The reduction of surface tension caused by protein adsorption facilitates the formation of new interfaces and further gas bubbles. The partially unfolded proteins associate while forming stabilizing film.

The ideal foam forming and foam stabilizing protein is characterized by a low molecular weight, high surface hydrophobicity good solubility, a small net charge is terms of the pH of the food, and easy denaturability. Foams are destroyed by liquid and organic solvents such as higher alcohols which due to their hydrophobicity displace proteins from the gas bubbles surface. A very low concentration of egg yolk prevents the bursting of egg white. This is attributed to the disturbance of protein associates by the lecithin.

The foam forming and foam stabilizing characteristics of protein can be improved by chemical and physical modifications. A partial enzymatic hydrolysis leads to smaller, more quickly diffusing molecules, better solubility and the release of hydrophobic groups.