THERMAL-DENATURATION OF WHEY PROTEINS IN SKIM MILK

Heat-induced denaturation of whey proteins, analyzed by reversed-phase HPLC, indicated that denaturation proceeds in two stages. The first stage of denaturation proceeds less rapidly than the second stage. Aggregation of whey proteins begins at about 70-degrees-C, and more aggregation was found to occur in sweet whey than in acid whey. The dimer of beta-LG and the beta-LG-alpha-LA complex were found to form preferentially in heated acid whey. Comparison of the second derivative Fourier transform infrared spectra of reconstituted skim milk and high-heat nonfat dry milk (NDM) powder (85-degrees-C) showed that heat treatment results in formation of two new bands (1684 and 1613 cm-1) in the amide I region at frequencies usually associated with intermolecularly hydrogen bonded-beta-sheets. The bands were smaller in sweet whey, compared with acid whey; difference spectra indicated that beta-LG was primarily responsible for the formation of heat-induced hydrogen bonding.