Casein

Casein is a family of phosphoproteins that make up about eighty percent of the protein in cow's milk, existing in solution as colloidal clusters called micelles held together by calcium ions and hydrophobic interactions; it is rich in the amino acid proline and has little tertiary structure, and it supplies amino acids, calcium and phosphorus as a food source. In cheesemaking, destabilizing casein with rennet or acid triggers coagulation into curds, the starting point for cheese, and it is also used as an emulsifier in ice cream and whipped toppings and historically as the basis of casein plastics such as galalith and casein fibers such as Lanital.