Synergy between ovalbumin and lysozyme leads to non-additive interfacial and foaming properties of mixtures

This study was undertaken to characterize the interfacial and foaming properties of different mixtures at the air–water interface under the same concentration range, and to put into light putative particular behaviors of mixtures. Different complementary techniques have been coupled such as null ellipsometry, surface tension and shear elastic constant measurements as well as polarization-modulation infrared reflection–absorption spectroscopy (PM-IRRAS). Moreover, the foaming properties were also investigated by a bubbling method. Solutions of either ovalbumin or lysozyme exhibit different interfacial behaviors. Ovalbumin does not form multilayers, even at high concentration. Conversely, lysozyme forms films that are much thicker than a protein monolayer whereas the surface pressure is definitely smaller than that ovalbumin. It thus seems that ovalbumin is much more surface active than lysozyme. The ellipsometric angles for the binary mixtures are much higher than those of films formed by the pure proteins, independently of the molar ratio. These results suggest that there is a synergy in the interfacial adsorption between the two proteins, which is confirmed by PM-IRRAS measurements, most likely due to the electrostatic interactions between the oppositely charged lysozyme and ovalbumin. Moreover, shear elastic constant measurements suggest that lysozyme has a strong effect on the organization of the interfacial film. The foaming properties of the mixtures are, however, always close to those of the pure ovalbumin solution. Therefore, lysozyme does not foam alone, but is able to foam as well as pure ovalbumin after addition of a very small amount of ovalbumin, which suggests that the synergy between proteins has an impact on the foaming properties.