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Comparison of Calcium Sensitivities of _s1-B, ß-A², and -A² Caseins and Their Stabilization by K-Casein A¹

Department of Animal Science, Texas A&M University, College Station 77843

ABSTRACT

Increasing concentrations of calcium increased precipitation of _s1-B, ß-A², and -A² caseins. However, differences occurred at various concentrations of added calcium. At low calcium (<4mM), -casein A² was more calcium-sensitive than either _s1-B or ß-A² casein. At high added calcium (15mM), only 55% of the -casein A² precipitated compared to 94 and 80% of the _s1-B and ß-A² caseins. Variations in calcium sensitivity were attributed to differences in average hydrophobicity and in phosphorus content of the three caseins. Solubilities of _s1-B, ß-A², and -A² caseins in the presence of 10 mM calcium increased with increasing concentrations of -casein A. In each case, the maximum solubility was near a -casein/calcium-sensitive casein ratio of .10. At ratios of -casein A/ß-casein A² and -casein A/-casein A² of .04 and greater, the solubility curves were similar. The ability of -casein to stabilize ß- and -caseins against precipitation by calcium was attributed primarily to hydrophobic interactions. Further work on -casein is needed.

¹ Technical article 11692 of the Texas Agricultural Experiment Station, College Station.

² Food Sciences Institute, Purdue University, Lafayette, IN 47907.