Editing Rancidification (section)

====Enzyme-catalysed oxidation====
A double bond of an unsaturated fatty acid can be oxidised by oxygen from the air in reactions catalysed by plant or animal [[lipoxygenase]] enzymes,<ref name="koon" /> producing a [[hydroperoxide]] as a reactive intermediate, as in free-radical peroxidation. The final products depend on conditions: the lipoxygenase article shows that if a [[hydroperoxide lyase]] enzyme is present, it can cleave the hydroperoxide to yield short-chain fatty acids and [[dicarboxylic acid]]s (several of which were first discovered in rancid fats).