Milk Enzymes

•        Each enzyme has a specific site of action on its target molecule, and optimal conditions (pH and temperature).
•         There are a large number of enzymes in milk and the functions of many are not well-defined.
•         It should be noted that the enzymes in milk do not make a major contribution to the digestion of milk in humans, which is accomplished by enzymes in the human stomach and small intestine.

Lipases:

•          Lipases are enzymes that degrade fats.
•         The major lipase in milk is lipoprotein lipase.
•         It is associated with the casein micelle.
•         Agitation during processing may bring the lipase into contact with the milk fat resulting in fat degradation and off-flavors.
•         Pasteurization will inactivate the lipase in milk and increase shelf life.

Proteases:

•         Proteases are enzymes that degrade proteins.
•        The major protease in milk is plasmin.
•         Some proteases are inactivated by heat and some are not.
•         Protein degradation can be undesirable and result in bitter off-flavors, or it may provide a desirable texture to the cheese during ripening.
•        Proteases are important in cheese manufacture, and a considerable amount of information is available in the cheese literature.

Alkaline Phosphatase:

•         Alkaline phosphatase is a heat-sensitive enzyme in milk that is used as an indicator of pasteurization. If milk is properly pasteurized, alkaline phosphatase is inactivated.

Lactoperoxidase

•         Lactoperoxidase is one of the most heat-stable enzymes found in milk.
•          Lactoperoxidase, when combined with hydrogen peroxide and thiocyanate, has antibacterial properties.
•         It is suggested that the presence of lactoperoxidase in raw milk inhibits the disease-causing microorganisms (pathogens) present in milk.
•         However, since there is no hydrogen peroxide or thiocyanate present in fresh milk, these compounds would have to be added to milk in order to achieve the antibacterial benefits.

Lysozyme:

•         Lysozyme is another enzyme that has some antibacterial activities, although the amount of lysozyme present in milk is very small.