Adsorption of α-lactalbumin and β-lactoglobulin on metal surfaces versus temperature

Abstract

The adsorption of α-lactalbumin and β-lactoglobulin on a hydrophilic chromium surface was followed in situ, using ellipsometry. The experiments were performed at temperatures up to and exceeding (in the case of α-lactalbumin) the thermal denaturation temperatures of the proteins. The denaturation temperatures and the reversibility of the denaturation of the proteins were estimated by differential scanning calorimetry (DSC). The residual transition enthalpy for the thermal denaturation of β-lactoglobulin, as a function of preheat time at temperatures dose to the denaturation temperature, was also recorded. In agreement with earlier reports, the denaturation of β-lactoglobulin was found to be irreversible, whereas the denaturation of α-lactalbumin was highly reversible. When approaching its denaturation temperature, the adsorption behavior of β-lactoglobulin indicates that an aggregation occurs at the surface starting after a time lag of several minutes. No such behavior was found for α-lactalbumin, where both the initial and the plateau values of the adsorbed amount increased gradually as a function of temperature. Preheated solutions of β-lactoglobulin had nearly the same adsorption behavior at 25°C as the native protein, while the thermally denatured form of α-lactalbumin seemed to be more surface active than the native.