Kinetic Study and Degradation Mechanism of Glycidyl Esters in both Palm Oil and Chemical Models during High-Temperature Heating

A kinetic model for glycidyl ester (GE) formation in both palm oil and chemical models during high-temperature heating was built to investigate the formation and degradation mechanisms of GEs in refined palm oil. The results showed that the formation and degradation of GEs followed pseudo-first-order reactions, and the rate constants of reaction kinetics followed the Arrhenius equation. The estimated activation energy of the GE degradation reaction (12.87 kJ/mol) was significantly lower than that of the GE formation reaction (34.58 kJ/mol), suggesting that GE degradation occurred more readily than formation. The Fourier transform infrared (FTIR) band intensities of epoxy and ester carboxyl groups decreased over heating time, while no band assigned to the cyclic acyloxonium group was found. Furthermore, no 5,5-dimethyl-1-pyrroline N-oxide (DMPO)-cyclic acyloxonium radical adduct was detected by quadrupole time-of-flight mass spectrometry (Q-TOF-MS). The above findings indicated that GEs were decomposed, fatty acid was also liberated, and GE degradation did not involve a cyclic acyloxonium intermediate. GEs were primarily decomposed into monoacylglycerol via ring-opening reaction during heating followed by fatty acid and glycerol via hydrolysis reaction.