κ-Casein

κ-Casein is the gatekeeper of the casein micelle: it coats the micelle surface with hydrophilic glycopeptide hairs that keep the particles dispersed in milk and stable against calcium-induced precipitation. Rennet’s chymosin clips these hairs at a single specific bond, and the denuded micelles aggregate into the curd that becomes cheese, which is why κ-casein is the molecular trigger of cheesemaking. Its genetic variants affect rennet coagulation time and cheese yield, and its glycosylation influences micelle stability during heating. In yoghurt manufacture, heat-denatured whey proteins complex with κ-casein to firm the gel. Few proteins illustrate so neatly how one molecule’s structure controls an entire food technology.