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Casein (/ˈksn/ KAY-see-n, from Latin caseus "cheese") is a family of related phosphoproteins (αS1, aS2, β, κ) that are commonly found in mammalian milk, comprising about 80% of the proteins in cow's milk and between 20% and 60% of the proteins in human milk.[1] Sheep and buffalo milk have a higher casein content than other types of milk with human milk having a particularly low casein content.[2]

Casein has a wide variety of uses, from being a major component of cheese, to use as a food additive.[3] The most common form of casein is sodium caseinate.[4] In milk, casein undergoes phase separation to form colloidal casein micelles, a type of secreted biomolecular condensate.[5]

Micelle casein

As a food source, casein supplies amino acids, carbohydrates, and two essential elements, calcium and phosphorus.[6]