Effects of Fe3+ and Antioxidants on Glycidyl Ester Formation in Plant Oil at High Temperature and Their Influencing Mechanisms.

This research investigated the effects of Fe3+ and antioxidants on the formation of glycidyl esters (GEs) and the free radical mediated mechanisms involving the recognition of cyclic acyloxonium free radical intermediate (CAFRI) for GE formation in both the plant oil model (palm oil, camellia oil, soybean oil, and linseed oil) system and the chemical model (dipalmitin and methyl linoleate) system heated at 200 °C. Results show that Fe3+ can promote the formation of GEs, which can be inhibited by antioxidants in plant oil during high-temperature exposure. Based on the monitoring of cyclic acyloxonium and ester carbonyl group by Fourier transform infrared spectroscopy, the promotion of Fe3+ and the inhibition of antioxidants (tert-butylhydroquinone and α-tocopherol) for GE formation occurred not only through lipid oxidation but also through directly affecting the formation of cyclic acyloxonium intermediate. Additionally, a quadrupole time-of-flight tandem mass spectrometry measurement was conducted to identify the presence of radical adduct captured by 5,5-dimethylpyrroline N-oxide, which provided strong evidence for the formation of CAFRI. Thus, one possible influencing mechanism can be that free radical generated in lipid oxidation may be transferred to dipalmitin and promote CAFRI formation. Fe3+ can catalyze free radical generation while antioxidants can scavenge free radical, and therefore they also can directly affect CAFRI formation.