Lipases and esterases EC

Lipases catalyse the development of hydrolytic rancidity in milk, and, consequently, lipases and lipolysis in milk have been studied extensively. Milk contains three types of esterase  

A-type carboxylic ester hydrolases (arylesterases EC 3.1.1.2), which hydrolyse aromatic esters, e.g. phenylacetate they show little activity on tributyrin, and are not inhibited by organophosphates. 

B-type esterases (glycerol tricarboxyl esterases, aliphatic esterases, lipases EC 3.1.1.3) they are most active on aliphatic esters although they show some activity on aromatic esters they are inhibited by organophosphates. 

In normal milk, the ratio of A B C esterase activity is about 3 10 1 but the level of A-esterase activity increases considerably on mastitic infection. A and C esterases are considered to be of little technological significance in milk. 

---