Reaction Kinetics of Thermal Denaturation of Whey Proteins in Heated Reconstituted Whole Milk

Reconstituted whole milk was heated using pilot-scale heating equipment. Kinetic and thermodynamic parameters for the irreversible denaturation of β-lactoglobulins A and B and α-lactalbumin were determined. α-Lactalbumin denaturation was first order, whereas both β-lactoglobulin variants had a reaction order of 1.5. Arrhenius plots for all three proteins showed an abrupt change in temperature dependence. In the low-temperature range, the thermodynamic parameters were ascribed to typical denaturation processes in which the unfolding of the protein tertiary structure is the rate-determining step. At higher temperatures, these parameters were in the range expected for typical condensation reactions, suggesting that aggregation processes may be rate-determining in this temperature range. The rate constants for β-lactoglobulin denaturation were independent of the initial protein concentration at all temperatures. For α-lactalbumin at temperatures below 85 °C the rate constants may have been dependent on the initial α-lactalbumin concentration as higher rate constants were observed with decreasing protein concentrations. Keywords: Whey protein; denaturation; whole milk; reconstituted milk