Heat Stability of Casein in the Presence of Calcium and Other Salts

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Abstract
The extent of calcium binding and the heat stability of colloidal suspensions of freeze-dried casein in calcium hydroxide solution, with added phosphates, citrates, and chlorides in some tests, was studied. The calcium-binding power of freshly prepared freeze-dried casein was greater (pK 4.5) than that reported for other casein preparations. However, the pK value decreased during storage of the casein at room temperature and within 1 or 2 mo. attained a value (pK = 3.0 [plus or minus] 0.3) in agreement with published values. The heat stability of simple casein caseinate suspensions was inversely related to the extent to which the casein was saturated with calcium, and this relation appeared to be linear at calcium levels sufficient to give over 80% saturation. The heat stability of more complex suspensions was inversely related to the ratio of soluble or ionic calcium to soluble phosphate in the suspension. Chlorides and phosphates of sodium, potassium, and ammonium displaced calcium from caseinate to about the same extent, but ammonium ion appeared to have a specific depressant effect on heat stability.