Isothermal and Scanning Calorimetry Measurements on β-Lactoglobulin

The denaturation and aggregation of β-lactoglobulin was studied by isothermal calorimetry. Experiments with several β-lactoglobulin concentrations (15−100 g/L) were performed at temperatures in the range 62−68.5 °C. Even a small change in temperature had a tremendous effect on the shape of the thermograms, depending also very strongly on the β-lactoglobulin concentration used. The measured thermograms were modeled using the kinetic model for the denaturation and aggregation of β-lactoglobulin recently developed by Roefs and De Kruif. In this kinetic model we recognize four consecutive steps: dissociation, unfolding, exchange of disulfide bonds, and aggregation. The numerical calculations yielded results that were in qualitative and quantitative agreement with typical experimental isothermal calorimetry curves. DSC curves and the decrease in concentration of native β-lactoglobulin as a function of time could also be reproduced well. We think that isothermal calorimetry, in combination with this kinetic model, provides a valuable and useful approach to the study of the denaturation and aggregation of β-lactoglobulin and other proteins.