Comparison of Calcium-Induced Associations of Bovine and Caprine Caseins and the Relationship of s1-Casein Content to Colloidal Stabilization: A Thermodynamic Linkage Analysis

¹ Cooperative Agricultural Research Center Prairie View A&M University Prairie View, TX 77446
² US Department of Agriculture, ARS Eastern Regional Research Center Philadelphia, PA 19118

In milk, _s1-, _s2-, ß-, and -caseins undergo association into colloidal complexes (casein micelles) that are visible with the electron microscope. Hydrophobic interactions and Ca²⁺ 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 _s1-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 (c.015 M). However, at increased calcium ion concentrations, these colloids are destabilized. Bovine casein (_s1-casein = 38% of total casein) was most stable with respect to added calcium ion concentration, and caprine casein, low in s1-casein (5% of total casein), was least stable. The high caprine (_s1-casein = 17% of total casein) was intermediate in stability. After destabilization, bovine casein was not resolubilized at elevated calcium concentrations, but both caprine caseins were. More casein from the low _s1-casein sample could be resolubilized (salted in). These results suggest a role for casein composition in dictating the functional properties of milks from various species.

Key Words: colloidal stability • calcium binding • casein • thermodynamic linkage analysis

Submitted on August 6, 1992
Accepted on June 14, 1993