A Review of Thermo-Oxidative Degradation of Food Lipids Studied by<sup>1</sup>H NMR Spectroscopy: Influence of Degradative Conditions and Food Lipid Nature
This review summarizes present-day knowledge provided by proton nuclear magnetic resonance (1H NMR) concerning food lipid thermo-oxidative degradation. The food lipids considered include edible oils and fats of animal and vegetable origin. The thermo-oxidation processes of food lipids of very different composition, occurring at low, intermediate, or high temperatures, with different food lipid surfaces exposed to oxygen, are reviewed. Mention is made of the influence of both food lipid nature and degradative conditions on the thermo-oxidation process. Interest is focused not only on the evolution of the compounds that degrade, but also on the intermediate or primary oxidation compounds formed, as well as on the secondary ones, from both qualitative and quantitative points of view. Very valuable qualitative and quantitative information is provided by 1H NMR, which can be useful for metabolomic and lipidomic studies. The chemical shift assignments of spectral signals of protons of primary (hydroperoxides and hydroxides associated with conjugated dienes) and secondary, or further (aldehydes, epoxides, among which 9,10-epoxy-12-octadecenoate [leukotoxin] can be cited, alcohols, ketones) oxidation compounds is summarized. It is worth noting the ability of 1H NMR to detect toxic oxygenated α,β-unsaturated aldehydes, like 4-hydroperoxy-, 4,5-epoxy-, and 4-hydroxy-2-alkenals, which can be generated in the degradation of food lipids having omega-3 and omega-6 polyunsaturated groups in both biological systems and foodstuffs. They are considered as genotoxic and cytotoxic, and are potential causative agents of cancer, atherosclerosis, and Parkinson's and Alzheimer's diseases.