Effects of Various Heat Treatments on Structure and Solubility of Whey Proteins

Structure and solubility of whey proteins are interrelated and affected by commonly used heat treatments.The relation between these characteristics, however, varies with the nature of the protein and the composition of the protein solution.After a brief analysis of structure and properties of the major whey proteins in the native state, attention is given to effects of thermal treatments (up to 150°C) on structure and solubility of the different whey proteins.It is pointed out that mild heat treatments up to 60°C may affect reversibly the solubility and foaming properties of whey proteins.Conformationat changes, as reflected by differential scanning calorimetry and observed above 60°C for a-lactalbumin and near 80 and 140°C for fl-lactoglobulin, however, exert more serious effects on the functional properties of whey proteins.Modifications of cystineresidues in the polypeptide chain are detected by amino acid anal~csis upon heat treatments above 100-C under identical heating conditions as used for differential scanning calorimetry.Special attention is given to the effect of changes of environmental conditions such as pH and the presence of lactose and calcium salts, to get more information on the complicated relation between structure and properties of proteins in whey.