Casein component in milk

Milk contains two major protein groups: caseins and whey proteins. Caseins, which occupy about 80% of the total protein in bovine milk, exist mainly in macromolecular complexes as casein micelles consisting of more than 1000 casein submicelles.

The casein proteins are the major component of milk true protein and are comprised of alpha S1 (αS1), alpha S2 (αS2), beta (β), kappa (κ), gamma (γ) caseins. Γ-casein is a product of the proteolytic degradation of β casein.

As caseins are polyelectrolytes, they are very susceptible to changes in pH. They have, in general, an isoelectric point in the region of pH 4.6. Changing the pH of skimmed milk from ~6.7 (natural pH) to 4.6 causes the caseins to self-aggregate on a macroscopic scale.

Caseins are known to be precursors of a number of different bioactive peptides. Casein is a group of phosphoproteins and consists of about 30 different components including genetic variants.

The casein micelle determines the colloidal stability of the polydisperse system in milk. The dimension and composition of casein micelles are of great importance for the coagulation process.
Casein component in milk