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Precipitation of Caprine and Bovine Caseins from Acidic Solutions by Sodium Polyphosphate: Influence of pH and Urea. Utilization for Separation of _s- and -caseins

Eastern Regional Research Laboratory, USDA, Philadelphia, Pennsylvania

ABSTRACT

The caseins, both caprine (goat) and bovine, are precipitated by relatively low concentrations (approximately 4 mg per 10 ml for a 0.5% casein solution at pH 2.0) of sodium polyphosphate. The casein precipitation is pH dependent (1.5 mg per 10 ml precipitates 50% at pH 2.0, whereas only 0.5 mg is required at pH 3.5), but this pH dependence is much less than that shown by sulfate precipitation of the caseins, -Casein in the presence of 2.0 M urea is not precipitated by polyphosphate; this concentration of urea has a neglible effect on the precipitation of _s-casein. This behavior provides a means for separating _s- and -caseins. Separation is facilitated by reducing the -casein to the monomeric form with mercaptoethanol. The caprine and bovine -caseins cannot be distinguished in the stabilization of _s-casein against precipitation with calcium ions.