Impact of structural changes and aggregation on adsorption kinetics of ovalbumin at the water/air interface

Abstract

Differential Scanning Calorimetry (DSC) was used to study the thermal stability of ovalbumin molecules at concentrations lying between 0.25% and 5% and at pH 3 and pH 7: critical temperatures such as temperature of the first increase in heat flow ( T i), peak temperature ( T p) and enthalpy change of heat reactions (Δ H app) were determined. The results indicated that T p did not vary significantly whatever the protein concentration, whereas the heat stability of protein conformational states was higher at pH 7 than at pH 3. These results were confirmed through the secondary structure changes upon heating, as monitored by circular dichroism measurements: at pH 3, we observed the formation of molecular species probably associated by intermolecular β-sheets at T⩽ T i. Electrophoretic patterns of preheated solutions indicated the formation of aggregates at T< T i (pH 3) and at T< T p (pH 7). The ability of the predenatured molecules to adsorb onto the air/water interface, as measured by the Wilhelmy balance, was shown to be closely related to their initial conformational states and aggregation properties before absorbing.