Heat stability of reconstituted milk protein concentrate powders

Milk protein concentrates (MPCs) were manufactured from skim milk at pilot scale by ultrafiltration, or ultrafiltration and diafiltration, to different protein concentration factors. MPCs were then spray-dried into seven powders ranging from 36.6% (w/w; MPC35) to 89.6% (w/w; MPC90) protein in dry matter. Powders were reconstituted to 3.5% (w/w) protein and the heat stability of MPC suspensions measured at 140°C in the pH range 6.3-7.3. At pH<6.8, the heat stability of MPC suspensions decreased with increasing protein content of the MPC powders, due to high Ca-ion activity. At pH>6.8, the destabilising influence of increased Ca-ion activity with increasing protein content of the MPC powders was countered partially by reduced heat-induced κ-casein dissociation. The heat stability of MPC80 was restored by re-establishment of the serum composition of skim milk; fortification with lactose or urea only affected heat stability outside the pH region where rapid Ca-induced coagulation occurred.