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.Keywords Oleic acid Á Thermal oxidation Á Temperature Á ESR Á Spin trapping J Am Oil Chem Soc (2019) 96: 937-944.

Electron Paramagnetic Resonance Spin Trapping of Sunflower and Olive Oils Subjected to Thermal Treatment: Optimization of Experimental and Fitting Parameters

“…In our experiment, this species was not detected, but we identified a species with a H 0.2081 mT. Similarly, other authors , observed during the thermal oxidation of oleic acid a DMPO adduct having a H 0.212 and 0.19921 mT and interpreted this splitting as due to the γ-hydrogen of an oxidized DMPO adduct where the β-hydrogen was lost. Besides the species with a H 0.2081 mT, we observed another species with only three lines.…”

Free-Radical-Mediated Formation Mechanism of Polar Polymeric Triglycerides in Vegetable Oil Studied by Electron Spin Resonance and High-Performance Liquid Chromatography

“…The intensity of alkyl radical adducts was kept the highest in the detection process. In our former study, the DMPO-oxidized radical adducts were also oxygen-centered radicals, which formed from the β-cleavage of alkoxyl radical adducts . With the comparison of the radical adducts formed in three kinds of vegetable oil, alkoxyl radicals formed in the initial stage.…”

“…In our former study, the DMPO-oxidized radical adducts were also oxygen-centered radicals, which formed from the β-cleavage of alkoxyl radical adducts. 27 With the comparison of the radical adducts formed in three kinds of vegetable oil, alkoxyl radicals formed in the initial stage. Then, alkyl radicals formed and accumulated to be the dominating free radicals.…”

“…ESR spectra of PO (A), RO (B), and SO (C) at different times (a: 2 min, b: 4 min, c: 12 min, and d: 30 min) are shown in Figure . The experimental spectra could be simulated by alkoxyl, alkyl, and DMPO-oxidized radical adducts. , In the ESR spectrum of PO at 2 min, DMPO-oxidized adducts were the main radical adducts, followed by alkyl radical adducts and alkoxyl radical adducts. The intensity of DMPO-oxidized radical adducts increased to 0.65 at 4 min, then decreased, and were almost nondetectable at 30 min.…”

Identification of Key Off-Flavor Compounds in Thermally Treated Watermelon Juice via Gas Chromatography–Olfactometry–Mass Spectrometry, Aroma Recombination, and Omission Experiments

“…(E)-2-decenal was employed as an aroma marker of oxidation degradation to quantitatively monitor and describe the quality of packaged olive oil [47]. (E)-2-Decenal also formed by oleic acid being degraded at 140 • C affects the flavor of frying [48,49]. It is derived from the thermal reaction of enzymatic hydrolysates of the protein with oxidized lard [50].…”