Lipolytic rancidity in milk

The term rancidity refers to ‘off’ odors and flavors resulting from lipid oxidation or lipolysis. Lipolysis is the process of breaking down of oils chemically or by lipase into constituent fatty acids. It entails hydrolysis whereby a triglyceride, for instance, is broken down into free fatty acids and glycerol.

Rancidity can be classified into 3 types such as hydrolytic rancidity, oxidative rancidity, and microbial rancidity.

Lipolytic rancidity in milk is caused by the liberation of C4-C12 fatty acids from milk fat by milk lipase or bacterial lipases. Terms to describe this off-flavor are soapy, rancid and butyric acid. Free fatty acids contribute to the desirable flavor of milk and milk products but, when present in high concentrations as a result of excessive lipolysis, can impart rancid off-flavors to the product.

Sometimes lipolytic rancidity is accompanied by bitterness as a result of the formation of certain mono- and diglycerides.

Lipoprotein lipase is active on the fat in natural milk fat globules only after their disruption by physical treatments or if certain blood serum lipoproteins are present. The major microbial lipases are produced by psychrotrophic bacteria.
Lipolytic rancidity in milk