SURFACE HYDROPHOBICITY CHANGES AND HEAT-INDUCED MODIFICATIONS OF ALPHA-LACTALBUMIN

A study on the thermal modification of the structure of a-lactalbumin was carried out on the calcium-containing and the calcium-free forms of the protein using different techniques, namely differential scanning calorimetry, intrinsic fluorescence, and spectrofluorometric determination of changes in the binding properties of the fluorophor 1,8-anilinonaphthalenesulfonate. A modification of this latter technique was used to study surface hydrophobicity changes while the proteins were heated at a given temperature and allowed the detection and the analysis of molecular modifications in the course of the heat treatment. Some of these modifications were found to differ from those made evident by other experimental approaches. Comparison of the E(a) values determined for the individual phases of the surface hydrophobicity changes in kinetic studies with those obtained by other methodologies suggests that the overall denaturation process-including the formation of aggregates and the precipitation of the protein in whey and skim milk-is related to the swelling of the protein structure in the early phases of exposure to heat.