The influence of milk minerals and lactose on heat stability and age-thickening of milk protein concentrate systems

Reconstituted milk protein concentrate (MPC; 80% protein) was mixed with lactose (MPC-Lac) or milk permeate (MPC-Perm) to 20% dry matter (DM) before been evaporated to 45% DM and subsequently spray dried. The pH of protein solutions, measured during evaporation from 20 to 45% DM at 50 °C, decreased from pH 6.64 to pH 6.53 and from 6.1 to 5.95 for MPC-Lac and MPC-Perm, respectively. The particle size and viscosity were greater in MPC-Perm than MPC-Lac solutions after evaporation. However, the heat stability of rehydrated MPC-Perm powder (3.5% protein) were significantly higher than MPC-Lac at pH values between 6.4 and 6.8, which may be attributed to the lower calcium ion concentration in MPC-Perm than in MPC-Lac. This study highlighted the complexity of mineral addition and phase distribution in protein-standardised milk systems; whereby higher levels of mineral addition contribute to viscosity and age thickening, but not necessarily lower heat stability.