Foaming behaviour of EDTA-treated α-lactalbumin

The foaming properties of partially denatured α-lactalbumin was investigated. The partially denatured state was produced by removing bound Ca2+ by treatment with ethylenediaminetetraacetic acid (EDTA) at pH 8.0 and 25°C. Surface tension measurements showed that partially denatured α-lactalbumin unfolds easily at liquid interfaces compared with the native protein. The results of foam volume and stability measurements were consistent with the results of surface tension measurements. In the presence of EDTA a considerable amount of foam was obtained at low concentrations, such as 0.1 mg/ml, and the foam stability was improved. This indicates the importance of the protein structure on the adsorption of molecules at liquid interfaces. The presence of Ca2+ also resulted in an increase in the foamability and foam stability of α-lactalbumin compared with native protein, due to the saturation of the surface charges. This shows the binding affinity of protein to Ca2+. The investigation of the effect of Ca2+ on the surface behaviour of β-lactoglobulin, another whey protein, also showed an improvement in the foaming properties of protein.