Effect of Various Salts on the Coagulation of Casein

Abstract

Summary Addition of potassium or sodium chloride (80 or 130m M ) to skimmilk increased the time the milk could be held in frozen storage without development of 4% precipitate by volume. Addition of phosphate or calcium (10m M ) had the opposite effect. Addition of large amounts of sodium chloride (up to 1.0 M ) offset the destabilizing effect of phosphate or calcium at 0, 10, and 20° F., but addition of similar amounts of potassium chloride stabilized the samples only at 10 and 20° F. Addition of potassium chloride (1.0 M or more) and of phosphate (100m M or more) induced gelation of milk at room temperature. Addition of sodium chloride and phosphate did not induce gelation. Addition of either potassium or sodium chloride (2.3 M ) shifted approximately 20% of the insoluble calcium and 7.5% of the insoluble phosphate to the soluble forms, displaced calcium from casein, and increased the dissociation of calcium citrate. A possible explanation of these effects, based on the interlinking of potassium-calcium-caseinate micelles by precipitating calcium phosphate, is presented.