Formation of hydroperoxy- and hydroxyalkenals during thermal oxidative degradation of sesame oil monitored by proton NMR

Detection of primary and secondary oxidation products by Fourier transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance (NMR) in sunflower oil during storage

The oxidation of sunflower oil, stored in closed receptacles at room temperature for a period of 10 years, was monitored using Fourier transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance (NMR). The objective was to understand the evolution of the oxidation process in sunflower oil under the conditions above mentioned. These techniques provide information about the oxidative status of several oil samples and the primary and some of the secondary oxidation products formed in the oxidation process. The results obtained show that, under these conditions, sunflower oxidation takes place in a different way to that at higher temperatures with aeration. The 1H NMR spectra show that in the first oxidation stages of the process only hydroperoxides supporting cis, trans-conjugated double bonds are formed and that at more advanced stages hydroperoxides having trans, trans-conjugated double bonds are generated, with the latter always being in a smaller proportion than the former. In addition, the presence of hydroxy derivatives supporting cis, trans-conjugated double bonds among the primary oxidation compounds is shown for the first time. Also, from early oxidation stages onward and unlike the process at 70 degrees C with aeration, it is noticeable that 4-hydroxy- trans-2-alkenals are formed in much higher proportions than 4-hydroperoxy- trans-2-alkenals. This fact could be associated with the presence of hydroxy derivatives with cis, trans-conjugated double bonds among the primary oxidation products and the limited concentration of oxygen during the oxidation. Furthermore, relationships between some oxidation conditions and the oxidation level of the samples were statistically analyzed.

Identification of volatile degradants in formulations containing sesame oil using SPME/GC/MS

Solid-phase microextraction (SPME), in combination with gas chromatography/mass spectrometry (GC/MS), was used to identify an unknown degradant observed during stability studies of a pharmaceutical formulation containing sesame oil. SPME is a solvent-less, rapid, sensitive, and inexpensive extraction method that minimizes sample preparation. SPME combined with GC is a widely used technique in certain fields, such as food, environmental analysis, forensics, and consumer products, but has only rarely been used for the analysis of pharmaceutical formulations. Hexanal, octanal, 2-octenal, 2-decenal, 2-undecenal, and 2,4-decadienal can be detected and identified by GC/MS, but they cannot be detected by LC/MS due to their volatility and low ionization efficiency under atmospheric pressure ionization conditions. Combining the MS data from the GC/MS with LC/DAD data resulted in the identification of the unknown degradant in the formulation as 2,4-decadienal. The presence of this and other aldehydes was attributed to the oxidative degradation of the unsaturated fatty-acid component in vegetable oils.

Study of both sunflower oil and its headspace throughout the oxidation process. Occurrence in the headspace of toxic oxygenated aldehydes

The static headspace composition of sunflower oil throughout the oxidation process at 70 degrees C with circulating air is studied by means of solid-phase microextraction followed by gas chromatography-mass spectrometry (SPME-GC-MS); at the same time the liquid phase of the same oil is studied by means of Fourier transform infrared (FTIR) spectroscopy. Each technique provides complementary information about the process; FITR spectroscopy detects changes in the functional groups of the liquid matrix in a global way and SPME/GC-MS provides information about the different components present in the volatile phase during the oxidation process. Concordance between the timing of the changes produced in both liquid and gaseous phases is observed, as well as agreement and complementarity in the results obtained from both phases. The formation of some well-known genotoxic and cytotoxic oxygenated aldehydes in this process and their presence in the oil headspace are proved.