COMPARISON OF CALCIUM-INDUCED ASSOCIATIONS OF BOVINE AND CAPRINE CASEINS AND THE RELATIONSHIP OF ALPHA(S1)-CASEIN CONTENT TO COLLOIDAL STABILIZATION - A THERMODYNAMIC LINKAGE ANALYSIS

In milk, alpha(s1)-, alpha(s2)-, beta-, and kappa-caseins undergo asso ciation into colloidal complexes (casein micelles) that are visible wi th the electron microscope. Hydrophobic interactions and Ca2+ bonding are among the major causes of colloidal complex formation. In model sy stems, stable colloidal casein micelles can be obtained in a calcium c aseinate solution by centrifugation at 1500 x g. The stabilities of co lloidal complexes of bovine and two caprine caseins, selected for thei r alpha(s1)-casein contents, were tested and thermodynamically linked with the calcium-induced changes in the amount of stable colloid prese nt. Analysis of the data according to this thermodynamic linkage appro ach for bovine and caprine caseins indicates colloid formation at low calcium concentrations (<.015 M). However, at increased calcium ion co ncentrations, these colloids are destabilized. Bovine casein (alpha(s1 )-casein = 38% of total casein) was most stable with respect to added calcium ion concentration, and caprine casein, low in alpha(s)1-casein (5% of total casein), was least stable. The high caprine (alpha(s1)-c asein = 17% of total casein) was intermediate in stability. After dest abilization, bovine casein was not resolubilized at elevated calcium c oncentrations, but both caprine caseins were. More casein from the low alpha(s1)-casein sample could be resolubilized (salted in). These res ults suggest a role for casein composition in dictating the functional properties of milks from various species.