Oxidative rancidity is defined as the oxidation of unsaturated lipids and the carbon-carbon double bond with the presence of typically oxygen gas. Sometimes aldehydes and ketones are released as products.
How does the presence of metal ions catalyze this reaction? What are, if any exist, the reaction intermediates?
Here are some of the things I thought about:
The reason why light favors the oxidative rancidity of lipids while temperature does not, (at least not as far as I know) may be an indication that the reaction can not occur with out ionized oxygen atoms, which photolysis of oxygen may produce. This will also explain why simply increasing the temperature will not work, since increase in temperature does not lead to an increase in oxygen ions. The presence of metal ions would than be hypothesized to assist the oxidative rancidity of lipids by helping with the formation of oxygen ions. However, that calls in question whether or not should the metal be ionized to start with, because if the metal ions were cations to begin with, say it is $Na^+$ from table salt, how would that increase the concentration of oxygen ions?