Protein–protein interactions: Their importance in the foaming of heterogeneous protein systems

Analysis of egg albumen foams by electrophoresis showed that the basic protein lysozyme (pI 10.7) was strongly retained. Addition of low concentrations (0.01–0.10% w/v) of the basic proteins clupeine (pI 12) and lysozyme to solutions (0.50% w/v) of several acidic proteins (pI 4.7–6.0) greatly improved their foaming properties at pH values between the isoelectric points. Sucrose strongly enhanced the action of the basic proteins, while not significantly affecting the foaming of the acidic proteins alone. Basic proteins did not enhance the foaming of ovalbumin and egg albumen in the absence of sucrose. Clupeine enhanced foaming more effectively than lysozyme under all conditions studied. Lysozyme was least effective near the isoelectric point of the acidic protein, where electrostatic interactions were weakest. Sodium chloride (0.1M) had a detrimental effect on the action of lysozyme.