Polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS), ellipsometry, and shearelastic constant measurements were used to study the adsorption and the behavior of ovalbumin andS-ovalbumin at the air-water interface at different values of the subphase pH. Native and S-ovalbuminexhibited similar behaviors, with a maximum plateau value of the shear elastic constant near the isoelectricpH of the protein. However, higher surface concentration values were reached with S-ovalbumin in lownet charge conditions, which suggest adsorption of aggregates or multilayer adsorption. For both proteins,the statistical analysis of PM-IRRAS spectra demonstrated that the aging of the interfacial film and theincrease of the shear elastic constant were correlated with a significant increase in the relative contributionof intermolecular‚-sheets in the amide I band with time. This increase was significantly faster at low pHvalues. At the same pH value and age of the interface, the relative contribution of intermolecular‚-sheetswas significantly higher for S-ovalbumin