General principle:

Oxidation is an irreversible process by which molecular oxygen combines with nutrients in food, a process which will decrease the quality of the food by creating rancidity. There are two types of rancidity: hydrolytic and oxidative. Hydrolytic rancidity is caused either by the reaction of lipid and water in the presence of a catalyst or by the action of lipase enzymes. The oxidative rancidity results from a more complex three-stage oxidation process involving oxygen and lipids. The three-stage oxidation can be described in terms of initiation, propagation and termination reactions. In the initiation phase highly active free radicals are formed by the influence of temperature, light or metal ions. The second step in the oxidation process is called the propagation phase since in every reaction, new reactive radicals are formed and a chain reaction is started. During the termination phase two radicals will combine and neutralize each other resulting in the formation of stable oxidation products. These stable products are the cause for the typical rancid odour of oxidized foods.

The oxidative rancidity in food can be prevented by the addition of antioxidants. Antioxidants are able to delay oxidation by absorbing the radicals themselves rather than allowing the oxidation of the fats/lipids in food.

This page has been prepared by Kemin Industries Inc. (WFP's corporate partner)