Monitoring the oxidation state evolution of unsaturated fatty acids in four microwave-treated edible oils by low-field nuclear magnetic resonance and 1H nuclear magnetic resonance

Edible oils oxidize during microwave heating, which may affect their nutritional value and safety. Exploring the oxidation mechanisms of unsaturated fatty acids in edible oils to determine which are suitable for microwave heating is therefore important. We used GC-MS, low-field NMR, and H-1 NMR techniques to study functionalgroup oxidation, the unsaturated fatty acid change law, and the distribution and migration of protons in various functional groups of four common vegetable cooking oils during microwave treatment. We show that the acid values of sunflower, soybean, peanut, and corn oil increased by 14%, 31%, 36%, and 101%, respectively, while the concentrations of malondialdehyde increased by 115%, 664%, 158%, and 333%, respectively, and the peroxide value fluctuated with increasing microwave power. The C16:0 concentrations of all four edible oils increased by more than 50%, and the concentration of polyunsaturated fatty acids decreased by more than 30% during microwave treatment; hence sunflower oil is the most suitable of the above-mentioned oils for daily microwave heating. In addition, we recommend the use of three characteristic functional groups to monitor the oxidative changes undergone by oils: olefinic H (CH = CH), diallyl CH2(CH = CH-CH2 -CH = CH), and allyl CH2(CH = CH-CH2).

Automated summary

During microwave heating, edible oils undergo oxidation, affecting their nutritional value and safety. Researching the oxidation mechanisms of unsaturated fatty acids in these oils is important for determining their suitability for microwave heating. An analysis of four common vegetable cooking oils showed that sunflower oil is the most suitable for daily microwave heating, based on changes in acid values, malondialdehyde concentrations, and fatty acid composition during microwave treatment. Monitoring three characteristic functional groups can help track the oxidative changes in oils.