Improvement of solubility and of emulsifying properties of milk proteins at acid pHs by esterification

Three milk proteins (beta -lactoglobulin, alpha -lactalbumin and beta -casein) were esterified to different extents with methanol, ethanol and propanol, then their solubility was studied in the pH-range of 3-10. Their emulsifying properties were also checked in the pH-range of 3-7 by measuring the oil-droplet size using laser light scattering. Solubility of all esterified proteins was improved in the acidic pH range (3-6). The magnitude of improvement was depending on the extent of esterification, the nature of the grafted ester group and the nature of the modified protein. Emulsifying activity and stability of esterified milk proteins in the acidic pH range of 3-5 were generally higher compared to the corresponding native proteins. This improvement was associated with the degree of solubility, the degree of esterification, the type of ester group grafted and the nature of the used protein. The highest emulsifying activity improvement was observed for methyl ester derivatives at pH 5 where the native proteins have poor emulsifying properties.