Oxidative rancidity II

Oxidative rancidity II
A mechanism for the autoxidation of a methylene-interrupted unsaturated system (e.g. linoleate) was proposed.

The various reactions that may occur are presented. In the initiation step, a hydrogen atom (H) is abstracted from the methylene carbon atom adjacent to a double bond. This reaction results in formation of a free radical.

The reaction is catalyzed by catalysts (trace metals, oxygen, light, etc) or enzyme (lipoxidase).

Catalysts are necessary otherwise the reaction would be too slow to be significant.

Factors affecting autoxidation of fats
One of the factors that affects the autoxidation of common food fats is the total number of unsaturated linkages in the sample.

However, the total amount of unsaturated may not be as important as the degree of unsaturation within a given molecule.

A fat high on linolenic acid (three double bonds) would be more susceptible to oxidation than one containing a similar amount of oleic acid (one double bond).

Oxygen is necessary for autoxidation of fats. At very low oxygen pressure, the rate of oxidation is approximately proportional to the pressure.

Therefore, removal of atmospheric oxygen from a fat or food product exerts a protective effect.

This is accomplished in the food industry by vacuum packing or packaging under an inert gas such as nitrogen.

All forms of light radiation from ultraviolet to the infrared region are conductive to fat oxidation.

Ultraviolet light has more pronounced effect than visible light due to higher energy of ultraviolet.

Packaging in lightproof containers or amber colored containers is the usual means of controlling the destructive effect of light.
Oxidative rancidity II