Aging of Vegetable Oils

Vegetable oils (such as olive oil) are not inert substances. Their chemistry evolves over time. To illustrate this aging of oils, here is the example of the degradation of a fatty acid commonly found in vegetable oils: oleic acid. Oleic acid is a fatty acid with a carbon chain of 18 carbon atoms and a double bond on carbon 9 (hence the name omega 9). In the presence of naturally dissolved oxygen in oils, light, or various chemical impurities, oleic acid undergoes peroxidation. See the diagram below. The peroxidized form of oleic acid is in equilibrium with a radical form (represented by the dot) that is unstable and reactive. It can react with other fatty acids (extramolecular reaction) or with the molecule that carries it (intramolecular reaction). Here we illustrate the case of an intramolecular reaction of the radical on the carbon chain of oleic acid.