Lipids can be oxidized by three main ways that include complex reactions: autoxidation, enzymatic-catalyzed oxidation and photo-oxidation.
Autoxidation is a spontaneous reaction between oxygen and the unsaturated lipids to form a lipid hydro-peroxide, which then undergoes further reaction with or without the participation of other compounds. The reaction leading to oxidative deterioration.
Metals are thought to play a key role in the initiation of autoxidation process, as it is difficult to eliminate traces of metals during food processing. Metal ions may originate from plant and animal tissues.
Autoxidation proceeds by a free radical chain mechanism involving three steps:
* Initiation step:
Initiation occurs as hydrogen is abstracted from an unsaturated fatty acid.
* Propagation step:
A phase of oxidation occurs by lipid-lipid interactions resulting in a magnification of radical formation.
* Termination step
A phase consists of the reaction between radicals or with other non-radical compounds to give rise to non-radical products.
Oxidation in fish and fish oil occurs as a result of because of high concentration of polyunsaturated fatty acid exposure to air. These fatty acids are more susceptible to radical initiated triple oxygen oxidation than monounsaturated fatty acids.
Fats in the early stages of autoxidation are edible, but unpalatable. Thereafter the degree of unpalatability increases until the odor and flavor become so repulsive that the fat cannot be eaten.
The oil, meat, fishery, dairy, and bakery industries suffer serious losses from autoxidation of their products.
Autoxidation in food
