Caseïnemicellen

Casein micelles are the colloidal assemblies that carry most of the casein proteins in milk. They form a stable, translucent suspension in bovine milk and many other species’ milks. Typical micelle diameters range from about 100 to 200 nanometers. They function as a reservoir for calcium and phosphate and as a carrier for nutrients.

Micelles consist mainly of four casein proteins: alpha-S1-casein, alpha-S2-casein, beta-casein, and kappa-casein. The four proteins assemble into a network stabilized by interactions and by colloidal calcium phosphate (CCP) nanoclusters that bridge casein molecules. Kappa-casein is located on the micelle surface and forms a stabilizing layer that provides steric and electrostatic stabilization.

During milk secretion, caseins assemble into micelles in the presence of calcium; CCP contributes to their cross-linking; surface charge is negative due to phosphate groups; pH around 6.6; they are stable until acidification or enzymatic action reduces repulsion.

Coagulation occurs by acidification or rennet action. When pH decreases to near the isoelectric point or when kappa-casein is cleaved by rennin, the micelles aggregate, expelling serum whey to form cheese curd. Cheese and yogurt production rely on this behavior.

Casein micelles influence milk texture, digestibility, and mineral delivery. Their size, composition, and CCP content can vary with breed, diet, and processing; industrial processing often involves heat treatment, pH adjustment, or proteolysis that affects micelle stability.