The heat stability of β-lactoglobulin (β-lg) is usually described with reference to a concentration-dependent pseudo-rate constant k. Kinetic and thermodynamic parameters for the irreversible denaturation of β-lg, in a whey protein mixture dissolved in Tris-HCl buffer, were examined over a wide temperature range 75–120°C and for degrees of denaturation [(Co-Ct)/Co] up to about 90%. The first-order kinetic model best described β-lg denaturation over the temperature range 75–85°C, whereas the second-order model applies in the range 90–120°C. A comparison between β-lg thermostability in buffer and literature data pertaining to more complex heating media (whey and milk), over the range 75–120°C, was carried out on the basis of changes in activation free energy (ΔG#), which itself takes into account changes in both activation enthalpy (ΔH#) and activation entropy (ΔS#). It was found that the thermal stability of β-lg in different media, and irrespective of the kinetic model assumed in the present study, can be ranked: buffer ≪ whey>milk for the temperature range 75–85°C. On the contrary, at the higher temperature range, 90–120°C, the ranking is buffer<whey<milk, when using the second-order model to describe the present data. For such comparisons to be valid the initial concentration of β-lg in various studies, as well as the reaction order applied, should be taken into consideration.
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Galani et al. (1997) studied this question.