A differential scanning calorimetric study of the thermal denaturation of bovine beta-lactoglobulin. Thermal behaviour at temperatures up to 100 degrees C.

The thermal behaviour of beta-lactoglobulin in aqueous solutions was followed by differential scanning calorimetry in the temperature range from 40 to 100 degrees C. From the results the following information is obtained. 1. The DSC thermograms show a large transition peak in the temperature range from 60 to 90 degrees C, which reflects the denaturation (unfolding) of beta-lactoglobulin. 2. From the peak surface an apparent denaturation enthalpy delta H = 230 +/- 15 kJ/mol is calculated at pH 6.5. 3. The temperature of maximum deflection of the DSC curve is dependent on the heating rate. Extrapolation to zero heating rate results in a denaturation temperature of 70.4 +/- 0.5 degrees C at pH 6.7. 4. A kinetic analysis of the DSC curves shows that the denaturation of beta-lactoglobulin is of the first order at temperatures between 65 to 72 degrees C. The apparent activation energy amounts to 343 kJ/mol, calculated according to the method of Kissinger. After comparison of the results with data from the literature, it was concluded that 70 degrees C is a critical temperature for the denaturation of beta-lactoglobulin. Above 70 degrees C the denaturation behaviour is changed, probably because of the starting of the aggregation process. This change is indicated by the transition temperature of the DSC curve at the corresponding heating rate.