Casein from bovine milk is a phosphoprotein and forms three-dimensional colloidal supramolecular micelles. There are four main types of casein which make up approximately 80% of the total protein in bovine milk: α-s1 casein, α-s2 casein, β-casein, and κ-casein. Casein is proposed to be the main protective constituent in milk. Casein is an amphiphilic protein.