The comparative heat stability of bovine beta-lactoglobulin in buffer and complex media
1997
Galani, D. | Owusu Apenten, R.K.
The heat stability of beta-lactoglobulin (beta-lg) is usually described with reference to a concentration-dependent pseudo-rate constant k. Kinetic and thermodynamic parameters for the irreversible denaturation of beta-lg, in a whey protein mixture dissolved in Tris-HCl buffer, were examined over a wide temperature range 75-120 degrees C and for degrees of denaturation [(C(o) -- C(t))/C(o)] up to about 90%. The first-order kinetic model best described beta-lg denaturation over the temperature range 75-85 degrees C, whereas the second-order model applies in the range 90-120 degrees C. A comparison between beta-lg thermostability in buffer and literature data pertaining to more complex heating media (whey and milk), over the range 75-120 degrees C, was carried out on the basis of changes in activation free energy (Delta G#), which itself takes into account changes in both activation enthalpy (Delta H#) and activation entropy (Delta S#). It was found that the thermal stability of beta-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 degrees C. On the contrary, at the higher temperature range, 90-120 degrees 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 beta-lg in various studies, as well as the reaction order applied, should be taken into consideration.
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