Comparison of Calcium-Induced Associations of Bovine and Caprine Caseins and the Relationship of αs1-Casein Content to Colloidal Stabilization: A Thermodynamic Linkage Analysis

In milk, O(sl-, O(s2-, {3-, and K-caseins undergo association into colloidal complexes (casein micelles) that are visible with the electron microscope. Hydrophobic interactions and ea 2 + bonding are among the major causes of colloidal complex formation. In model systems, stable colloidal casein micelles can be obtained in a calcium caseinate solution by centrifugation at 1500 x g. The stabilities of colloidal complexes of bovine and two caprine caseins, selected for their O(sl-casein contents, were tested and thermodynamically linked with the calcium-induced changes in the amount of stable colloid present. Analysis of the data according to this thermodynamic linkage approach for bovine and caprine caseins indicates colloid formation at low calcium concentrations .015 M). However, at increased calcium ion concentrations, these colloids are destabilized. Bovine casein (O(sl-casein = 38% of total casein) was most stable with respect to added calcium ion concentration, and caprine casein, low in O(slcasein (5% of total casein), was least stable. The high caprine (O(sl-casein = 17% of total casein) was intermediate in stability. After destabilization, bovine