Effect of NaCl on some physico-chemical properties of concentrated bovine milk

The influence of added NaCl (75-850 mmol L^-1) on some physicochemical properties of 2× or 3× concentrated milk (18 or 27%, w/v, total solids, respectively) was investigated. Adding NaCl did not influence average casein micelle size, but reduced the net-negative charge on the casein micelles and milk pH. The level of soluble and ionic calcium was increased by addition of NaCl, but the level of soluble inorganic phosphorus was not influenced. Addition of NaCl shifted the maximum in the pH-heat coagulation time (HCT) profile of 2× or 3× concentrated milk to a higher pH value and certain concentrations increased the maximum HCT, probably due to the fact that NaCl reduced the extent of heat-induced dissociation of κ-casein. Added NaCl reduced the ethanol stability, with the extent of this effect increasing with the concentration of NaCl. The key-mechanism though which added NaCl induces changes in the physico-chemical stability of casein micelles appears to be through changes in the charge on the casein micelles.