Bovine milk contains a native lipoprotein lipase (LPL) that preferentially acts on emulsified substrates at water–oil interfaces and several esterases that preferentially act on soluble ester substrates. The lipase is by far the most abundant, most studied, best characterized, and of most practical significance. It is synthesized in the mammary gland and transported to the milk where, under certain circumstances, it catalyzes the hydrolysis of triacylglycerols to free fatty acids and mono- and diacylglycerols. It is mostly bound to the casein micelles but can move to the milk fat globule membrane under conditions that induce lipolysis of the globular fat. It is a glycoprotein of molecular mass 100 kDa and requires lipoproteins or apolipoproteins for full activity. By contrast, the esterases in milk are not well characterized. They are present in low concentrations except in abnormal milks such as colostrum and mastitic milks. The types reported include arylesterases, carboxylesterases, and cholinesterases. They seem to have no significant technological importance in milk. Human milk contains a relatively high concentration of a bile salt-stimulated lipase, in addition to LPL, which does not appear to be present in bovine milk. It has a role in the digestion of milk fat in neonates.
Encyclopedia of Dairy Sciences (Second Edition)