Solutions of a whey protein mixture were subjected to various time/temperature treatments, at pH 6.7. Kinetic and thermodynamic activation parameters for the rates of irreversible denaturation/aggregation of the principal whey protein component-␤-lactoglobulin (␤-lg) were followed by gel permeation. Fast Protein Liquid Chromatography (non-dissociating, non-reducing conditions) and by SDS-PAGE (dissociating, non-reducing conditions). The rate of loss of native ␤-lg owing to the formation of disulphide linked protein aggregates (k S D S -P A G E ) and the rate of formation of aggregates via both covalent and non-covalent bonds (k G P -F P L C ) showed similar biphasic Arrhenius plots. However, the break of the plot occurred at different points. The k G P -F P L C values were higher than values of k S D S -P A G E for all the temperatures examined. There was a similar trend for the thermodynamic activation parameters implying that not all of the ␤-lg aggregates through thiol-disulphide interactions. Hydrophobically driven associations occur within the aggregates.

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