Thermal Oxidation Rate of Oleic Acid Increased Dramatically at 140 °C Studied using Electron Spin Resonance and GC–MS/MS

Abstract Thermal oxidation of oleic acid at high temperatures was studied using combination of electron spin resonance (ESR) spin‐trapping technique and solid phase microextraction (SPME)‐Gas chromatography‐mass spectrometry‐mass spectrometry (GC–MS/MS). Dimethyl pyridine N‐oxide (DMPO) was applied as the spin trap. Alkyl, alkoxyl, and oxidized DMPO adducts were identified in the experimental spectra. At 140 °C, the alkyl radical adduct was the major component, accounting for 63.89% of the total radical adducts. However, the alkoxyl radical adduct was the main radical adduct in the temperature range of 120 to 135 °C. The total amount of spins, a parameter to indicate radical concentrations, detected at 140 °C was nearly three times higher than that at 135 °C. And, the total amount of alkyl radical adducts was higher than that of alkoxyl radical adducts at 140 °C, which indicated a higher alkyl radical formation rate. Besides, a larger amount (10.30%) of oleic acid degraded at 140 °C than that at 135 °C with the detection of GC. More (E)‐2‐Decenal (plastic) and (E)‐2‐undecenal (herbaceous) formed affect the flavor of frying.