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Interaction of _s-Casein with -Casein in Model Systems Before and After Freezing¹

Agricultural Products Utilization Biochemistry, Department of Animal and Range Sciences, Montana State University, Bozeman

ABSTRACT

Model systems containing ratios of 0.03 to 0.10 -/_s-caseins were prepared from combinations of 0.10 M CaCl₂, 3.19% NaH₂PO₄ (3.50 mg P/ml), 2.20% Na-citrate (20 mg citric acid/milliliter), 4.64% NaCl (28 mg Cl/milliliter), and 32% lactose. These systems were adjusted to pH 6.6–6.8 and their stability measured in terms of per cent soluble _s-casein both before and after freezing for 24 hr at 10 F.

The stability of <xs-casein increased directly with increase in - to _s-casein ratio in the presence of 0.02 M Ca. Addition of 0.20% citrate along with Ca caused a 14% increase in soluble _s-casein, whereas addition of citrate plus 16% lactose increased it by 45%. Addition of 0.035% P along with Ca resulted in 11% loss in _s-casein solubility. More drastic losses (about 18%) resulted from addition of 0.14% Cl to Ca. Freezing of the above systems caused a substantial loss in _s-casein solubility, except in those containing Ca + citrate + lactose.

In absence of calcium ions, -casein stabilized _s-casein to an extent dependent on the ionic species present.

¹ A contribution from Montana State University, Agricultural Experiment Station, Paper no. 768, Project no. 1351.