Deep frying and the use of same oil for frying many times is a general practice mostly in commercial and sometimes in domestic cooking processes. This practice generates lipid per- oxidation products that may be harmful to human health. Most of these compounds are non-volatile, so they remain in the frying medium and affect its physical properties at elevated temperatures in the presence of air and moisture causing the oxidative degradation of their amino acids and the partial con- version of these lipids to volatile chain-scission products, non- volatile oxidized derivatives and dimeric, polymeric or cyclic substances leading to the formation of toxic and/or carcino- genic compounds.