Foaming properties of egg white proteins affected by heat or high pressure treatment

This paper deals with the effect of heat (50–85 °C) and high pressure treatment (400–700 MPa at 10–60 °C) on the foaming properties of egg white solutions (10% v/v or 9.64 mg protein/mL). These physical treatments (20 min) were performed at two pH levels: pH 7.6 corresponding to the pH of fresh egg white and pH 8.8, corresponding to that of older egg white. Both heat and pressure treatment affected the foaming properties of egg white proteins. While foams from untreated egg white solutions were crispy and subject to collapse of the foam column after a long standing period, foams from heat and pressure-treated egg white solutions were moist and creamy, showing smaller bubble size and little or no sensitivity to foam collapse. The effect of physical treatments was strongly dependent on the pH during treatment. The most voluminous foams were obtained at pH 8.8, while the most stable, dense foams were obtained at pH 7.6, for both heat and pressure treatment. Based on previous data on the effect of heat and pressure treatment on the physicochemical properties of egg white proteins, the relationship between the processing-induced changes in these physicochemical properties and the foaming properties of egg white was investigated. Treatments resulting in a high level of protein unfolding, yet accompanied by a certain degree of residual protein solubility (primarily at pH 8.8), resulted in egg white solutions with improved foaming ability. A high level of unfolding combined with extensive protein solubility loss (primarily at pH 7.6) was associated with increased foam stability and density. Foams with high volume and average stability and density were obtained by pressure treatment at pH 8.8 (above 500 MPa). The processing-induced changes in the foaming properties could not be attributed to the changes in a single physicochemical property. The foaming ability was in part determined by the sulfhydryl content and protein flexibility. Improved protein–protein interactions (solubility and exposed SH groups) contributed to increased foam stability of treated egg white solutions. Other properties, not measured in this study, probably also contribute to the foaming properties of processed egg white solutions, especially after pressure treatment.