Enzymes in milk

Milk contains more than 60 different indigenous enzymes. Indigenous milk enzymes are found in or associated with a virus casein micelles, milk fat globule membrane, milk serum or somatic cells and may originate from blood, somatic ells, the MFGM or the cell cytoplasm.

Many enzymes found commonly in milk are not intrinsic milk enzymes, but are in milk because of the presence of microorganisms.

Pasteurization eliminates most natural enzyme activity in milk.

The two groups of enzymes of major economic importance are proteinases and lipases, including phospholipases, which are produced extracellularly and can act on micellar casein or on milk fat globules.

Besides microbial enzymes, milk also contains a natural proteinase and lipase. The milk lipase is inactivated by pasteurization, while the alkaline milk proteinase is heat stable and survives low-temperature short-time pasteurization conditions.

Other milk enzymes are stable; plasmin, for example, loses only 60% of its activity after 15 sec at 100 °C. Plasmin is the predominant indigenous proteinase in milk. It is part of a complex protease system in milk, consisting of its inactive, precursor, plasminogen, plasminogen activators, which catalyze the conversion of plasminogen to plasmin, plus inhibitors of plasmin and plasminogen activators.

Plasmin and plasminogen originate from the mammal’s blood and are predominantly associated with the casein micelle in milk.
Enzymes in milk