Detection of Primary and Secondary Oxidation Products by Fourier Transform Infrared Spectroscopy (FTIR) and ¹H Nuclear Magnetic Resonance (NMR) in Sunflower Oil during Storage

Abstract

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.

A review of analytical methods measuring lipid oxidation status in foods: a challenging task

“…Infrared (IR) spectroscopy is also known as a very helpful way to study lipid degradation under oxidative conditions [113], particularly since it is an easy, rapid, economical and non- IR has been applied to measure the peroxide value in oxidized lipids [115] and differences were found in the IR spectra of fresh and aged oils [116,117]; so IR spectra can be used to characterize the aging of various edible oils [118][119][120][121][122]. The investigation of the FTIR spectra of the treated oils revealed that the microwave heating of oils [123] caused significant changes in the intensities of their absorption bands and produced no shifts in the position of the bands.…”

Monitoring the oxidation of almond oils by HS-SPME–GC–MS and ATR-FTIR: Application of volatile compounds determination to cultivar authenticity

“…As mentioned in previous papers (Guillén & Goicoechea, 2007), a great deal of information about the oxidative status of oils can be obtained by studying the frequency and absorbance values of several bands of their infrared spectra. Fig.…”

“…(c) 1800-1700 cm À1 : This band in non-oxidised almond oil is solely due to the ester carbonyl functional group of triglycerides. In oxidised oils, it overlaps with that of aldehydes causing a decrease in the frequency value of the resulting band in relation to the first (Guillén et al, 2007). (d) 1000-900 cm À1 : The absorbance of the band in raw almonds is associated with bending vibrations of CH functional groups of isolated trans-olefins.…”

Thermal oxidative process in extra-virgin olive oils studied by FTIR, rheology and time-resolved luminescence

“…EVOO2 (not reported) showed an intermediate behaviour. In both native samples the presence of bands at about 3470 and 3530 cm À1 is revealed; the first is assigned to the overtone of the glyceride ester carbonyl absorption, the second to the presence of significant proportions of secondary oxidation products, such as alcohols, aldehydes or ketones (Guillèn & Cabo, 2000;Van de Voort, Ismail, Sedman, & Emo, 1994) and in particular to the stretching of OH groups (Borchman & Sinha, 2002;Guillèn & Goicoechea, 2007). During the first phase of thermal oxidation, the band at 3468 cm À1 becomes wider and more intense because of the appearance of the component at 3435 cm À1 due to the formation of hydroperoxides or primary oxidation products.…”