Concentration effects on the kinetics of beta-lactoglobulin heat denaturation: a differential scanning calorimetric study

The heat denaturation of beta-lactoglobulin dispersed in distilled water at concentrations from 3.5% to 24% (pH 3.2) was studied by differential scanning calorimetry. The activation energies, determined from Kissinger's and Borchardt and Daniel's methods. are in approximate agreement. The half reaction times of the native beta-lactoglobulin. calculated from the experimental parameters E(A) (activation energy). Z (pre-exponential factor) and n (apparent reaction order), were checked by an isothermal method. The results were in good agreement, except at the lowest concentration (3.5%). Peak temperatures, apparent enthalpy changes, widths at the half-height of the peaks and half reaction times tend to decrease with increasing concentration. The results indicate that inter-chain interactions play a larger role in the whole process, when the concentration increases and when the scanning rate decreases. This process can be modelled as a second-order reaction and a mechanism is suggested implying the dimerization of partly denatured beta-lactoglobulin molecules as a rate-limiting step.