A Review of Thermo‐Oxidative Degradation of Food Lipids Studied by ¹H NMR Spectroscopy: Influence of Degradative Conditions and Food Lipid Nature

Abstract

This review summarizes present-day knowledge provided by proton nuclear magnetic resonance ( 1 H 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 1 H 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 1 H 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.

New 1H NMR-Based Technique To Determine Epoxide Concentrations in Oxidized Oil

“…The chemical shifts of epoxides (2.90−3.24 ppm) were distinct from other oxidation products including alcohols (3.43−3.62 ppm), conjugated dienes (5.40−6.58 ppm), double bonds conjugated with carbonyls (6.08−6.82 ppm), hydroperoxides (8.30−8.90 ppm), and aldehydes (9.49−9.79 ppm). 29 In summary, 1 H NMR can be used to detect epoxides in oxidized soybean oils with superior selectivity, which is a major advantage over the chromatography method.…”

1H–13C HMBC NMR experiments as a structural and analytical tool for the characterization of elusive trans/cis hydroperoxide isomers from oxidized unsaturated fatty acids in solution

“…In the absence of sufficient quantities of chain‐terminating lipid soluble antioxidants, hydroperoxides are degraded to a wide variety of secondary oxidation products such as saturated and unsaturated aldehydes and oxo and hydroxy acids. Even for a simple monounsaturated lipid, such as oleate, the oxidation may lead to a variety of hydroperoxides and terminal oxidation products . The problem of oxidative deterioration is also of great economic importance in the production of lipid containing foods, because oxidation of unsaturated lipids produces offensive odors and imparts flavors, which also reduce its nutritional quality and safety.…”

Use of ATR-FTIR spectroscopy to detect the changes in extra virgin olive oil by adulteration with soybean oil and high temperature heat treatment

“…On the one hand, in the course of high temperature exposure, the oil undergoes severe changes including thermo-oxidation, cis-trans isomerisation, cyclization, polymerization and hydrolysis. On the other hand, the changes are difficult to predict because of the large numbers of variables involved, depending on the oil composition and the specific process conditions [10][11][12].…”