kasein

Casein, sometimes spelled kasein in some languages, is a family of phosphoproteins that forms the major protein fraction of milk. In cow’s milk it accounts for about 80% of the total protein and is organized into casein micelles, large colloidal aggregates stabilized by calcium phosphate and enveloped by whey proteins. The four principal types are alpha-s1-casein, alpha-s2-casein, beta-casein, and kappa-casein, each contributing distinct functional properties to milk and dairy products.

Casein's key role in dairy processing is its ability to coagulate and form curds. Rennet cleaves the kappa-casein on the micelle surface, destabilizing the micelle and causing coagulation to produce cheese. Acidification can also precipitate casein, a process exploited in yogurt and other cultured dairy products. In food manufacturing, soluble caseinates such as sodium caseinate and calcium caseinate are used as emulsifiers, stabilizers, and texturizers.

Nutritionally, casein provides a high-quality source of essential amino acids and is relatively slowly digested, yielding a steady release of amino acids. It also supplies minerals such as calcium and phosphorus bound within the micellar structure. Some individuals have cow’s-milk protein allergies or intolerances to casein, requiring avoidance of dairy ingredients. Beyond nutrition, casein and its derivatives find widespread use in processed foods and various industrial applications.