Effect of garlic essential oil on sunflower oil oxidative stability during accelerated storage studied by FTIR spectroscopy

Abstract

Garlic essential oil (GEO) was added to sunflower oil at different concentrations (0.005%, 0.5%, 10%) and enriched and non-enriched oils were subjected to accelerated storage (70 °C). Oil samples were studied daily by Fourier Transform Mid-Infrared (FTIR) spectroscopy. The changes in the frequency values and absorbance of specific bands of the spectra allowed to shed light on the effect of GEO on oil oxidative stability, in a very simple, fast and accurate way, providing information on the degradation of cis-double bonds of unsaturated acyl groups (band near 3008 cm−1), as well as on the generation of oxidation compounds like hydroperoxides (band near 3469 cm−1) and aldehydes (band near 1746 cm−1). Moreover, GEO composition was studied by Proton Nuclear Magnetic Resonance spectroscopy (1H NMR) and by Solid-Phase Microextraction coupled with Gas Chromatography-Mass Spectrometry (SPME-GC/MS). The main GEO components identified were sulphur-containing compounds (diallyl-disulfide, diallyl-trisulfide, methyl-allyl-disulfide …). The addition of GEO at 0.005% did not affect oil oxidative stability; at 0.5%, it provoked a decrease in oil oxidative stability; and the addition of 10% GEO increased it, causing remarkable differences in the oxidation process compared to the other oils under the same storage conditions. The present study evidences that under accelerated storage conditions the antioxidant efficacy of GEO depends on the concentration added to sunflower oil. This study also underscores the need for careful evaluation of the effect of potential antioxidants, emphasizing the usefulness of FTIR to follow the changes occurring in edible oils during oxidation under accelerated storage conditions.