Sequential adsorption of egg-white proteins at the air–water interface suggests a stratified organization of the interfacial film

The aim of this work was to get further insight into the formation of the interfacial film by ovalbumin and lysozyme in equimolar binary solutions, as well as the organization of these proteins inside the interfacial film. Our approach consisted in the sequential adsorption of the two proteins, with or without previous replacement of the sub-phase with protein-free buffer before injection of the second protein. The results suggest that ovalbumin controls surface pressure of the interfacial film and whatever the order of adsorption, there would be a specific and stratified organization of the two proteins inside the interfacial film: an ovalbumin monolayer in direct contact with the air–water interface and multilayers of lysozyme below this top layer. The experiments of replacement of the sub-phase suggest that, for both proteins, the adsorption film is almost resistant to this replacement with protein-free buffer, showing an apparently irreversible adsorption for the time-scale considered and at high concentrations. Moreover, the synergy between ovalbumin and lysozyme put into evidence during the concomitant adsorption of the two proteins in a previous work (Le Floch-Fouéré et al., 2009, Food Hydrocolloids 23, 352–365) is a phenomenon which occurs as the result of adsorption of the proteins at the air–water interface.