Degradation of monocarbonyls from autoxidizing lipids

Abstract

Abstracts In an attempt to account for carbonyls found in oxidized lipid systems, but not theoretically predicted from the decomposition of lipid hydroperoxides, a member from each of the monocarbonyl classes commonly observed in oxidizing lipids was oxidized at 45C in a Warburg apparatus and the carbonyl products studied. The carbonyl compounds used were n ‐nonanal, n ‐non‐2‐enal, n ‐hepta‐2,4‐dienal and n ‐oct‐1‐en‐3‐one. Nonanal was relatively stable to oxidation and was oxidized to nonanoic acid. Oct‐1‐en‐3‐one did not absorb oxygen during a 52‐hr period; however, the unsaturated aldehydes oxidized at faster rates than methyl linoleate or linolenate. Non‐2‐enal upon absorption of 0.5 mole of oxygen was oxidized almost quantitatively to non‐2‐enoic acid. Hepta‐2,4‐dienal was polymerized at 0.5 mole of oxygen uptake. In addition both of the unsaturated aldehydes produced shorter chain mono‐ and dicarbonyls as oxidative degradation products. The identification of these compounds helps to explain the presence of carbonyls in oxidizing lipids and model systems that are not accountable through the decomposition of theoretically predictable isomeric hydroperoxide esters. The relatively large yield of malonaldehyde from the oxidized dienal suggests that these carbonyls may serve as a major source of malonaldehyde in oxidizing diene esters. Significant quantities of malonaldehyde are not observed in methyl linoleate until late stages of oxidation, and the dienals formed through degradation of primary hydroperoxides may in turn oxidize to give malonaldehyde.