Heat stability of concentrated skim milk

Heat-induced coagulation of concentrated skim milk was studied. Heat-induced changes in partition between serum and colloidal particles of calcium and phosphate and of the various proteins were investigated as a function of heating time and conditions like pH, addition of phosphate and preheating. Aggregation of casein micelles upon heating was assessed by various methods, both at 120°C and after cooling to 20°C. A qualitative model for heat-induced coagulation of concentrated skim milk was proposed, which largely explained phenomena like the effects of pH, addition of phosphate and preheating. For concentrated skim milk produced from preheated milk, this model was also discussed semi-quantitatively. It is shown that the geometry of the emerging aggregates influences time of visible coagulation as much as the rate of aggregation of casein particles.