Effects of storage temperature on the solubility of milk protein concentrate (MPC85)

The effect of storage time and temperature on the solubility of milk protein concentrate (MPC85) was investigated using solubility tests, gel electrophoresis and mass spectrometry. It was found that, at a given temperature, the solubility of MPC85 decreased exponentially with time and a master curve was obtained using a temperature–time superposition. Gel electrophoresis indicated that the insoluble proteins were the caseins, whereas the whey proteins remained soluble. Mass spectrometry showed that, with storage time, the casein was lactosylated. In the light of these measurements, it is speculated that the insolubility of the MPC85 could have been due to cross-linking of the proteins at the surface of the MPC85 powder. However, other mechanisms, such as the cross-linking of the proteins by hydrophobic and/or hydrogen bonding, are not ruled out.