parakappacaseïne

Parakappacaseïne, also written parakappa-casein, is a proteolytic fragment derived from kappa-casein, one of the main milk caseins that stabilize the casein micelle. It is formed when kappa-casein is cleaved by proteolytic enzymes such as chymosin (rennet) during cheese production.

The enzymatic cleavage occurs at the Phe105–Met106 bond of bovine kappa-casein, yielding para-kappa-casein (the N-terminal fragment) and gamma-casein (the C-terminal fragment). Para-kappa-casein remains associated with the micelle surface, while gamma-casein is released into the whey as the micelle surface is destabilized. This cleavage reduces the steric stabilization of micelles and promotes coagulum formation, which is the basis of rennet-induced cheese coagulation.

In dairy science, para-kappa-casein is considered a transient intermediate rather than a stable protein; its presence and subsequent conversion influence curd texture and yield. The extent of para-kappa-casein formation depends on factors such as enzyme type and activity, milk composition, pH, calcium concentration, and temperature.

Parakappacaseïne is primarily discussed in the context of bovine milk but can also occur in milks of other ruminants. It is related to but distinct from intact kappa-casein and from gamma-casein.