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

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 degrees 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 degrees C. The total amount of spins, a parameter to indicate radical concentrations, detected at 140 degrees C was nearly three times higher than that at 135 degrees C. And, the total amount of alkyl radical adducts was higher than that of alkoxyl radical adducts at 140 degrees C, which indicated a higher alkyl radical formation rate. Besides, a larger amount (10.30%) of oleic acid degraded at 140 degrees C than that at 135 degrees C with the detection of GC. More (E)-2-Decenal (plastic) and (E)-2-undecenal (herbaceous) formed affect the flavor of frying.