Introduction to Chemistry of Lipids

2.12. Rancidity

Rancidity also called Rancidification, is a condition that is produced by the aerial oxidation of unsaturated fat present in foods and also other products that are marked by unpleasant flavours or odours. When unsaturated components of a fatty material are exposed to sunlight, they can be converted into hydroperoxides, which break down into esters, volatile aldehydes, ketones, alcohols, and hydrocarbons, some of which have unpleasant odours.

How does a food become rancid?

Rancidity, in general terms, is always used for food products that have oil and fatty acids in them. Fatty acids are generally composed of fats, cholesterol and steroids. 

These are mostly carboxylic acids that consist of a long aliphatic chain. They are either saturated which means there is only a single linkage between the carbon atoms or unsaturated that comprises multiple linkages between the carbon atoms.