Monitoring of the oxidation process of egg yolk phospholipids at frying temperature by nuclear magnetic resonance

Abstract

Egg yolk phospholipids (EPLs) are sensitive to oxidation and can produce large quantities of volatile compounds. This study monitored the oxidation process of EPLs at frying temperature. The changes in the classes of EPLs, molar percentages of their fatty acyl groups and the concentrations of oxidation compounds under frying temperature were monitored by 31P nuclear magnetic resonance (NMR) and 1H NMR. Meanwhile, egg yolk triglycerides (ETGs) were used as controls. EPLs were mainly composed by phosphatidylcholine (76.74% ± 1.48%), phosphatidylethanolamine (17.97% ± 1.40%) and phosphatidylserine (1.26% ± 0.55%). EPLs, especially phosphatidylethanolamine, were degraded significantly during heating. The molar percentages of unsaturated acyl groups in EPLs were decreased, while the percentages of saturated plus modified acyl groups were increased during heating. EPLs produced large quantities of hydroperoxides and secondary oxidation compounds quickly. The results proved that EPLs were more sensitively to oxidation than ETGs during frying process, and EPLs could generate abundant of secondary oxidation compounds, especially 2,4-alkadienals, which demonstrated that EPLs are an ideal precursor of lipid-derived odorants.