Abstract
The minor components of vegetable oils are important for their oxidative stability. In order to know to what extent they can influence oil behaviour under oxidative conditions, two commercial soybean oils, one virgin and the other refined, both with very similar compositions in acyl groups but differing in their minor component profiles, were subjected to accelerated storage conditions. They were characterized by 1H nuclear magnetic resonance (NMR) and direct immersion solid-phase microextraction coupled to gas chromatography/mass spectrometry (DI-SPME-GC/MS), while oil oxidation was monitored by 1H-NMR. The lower levels of tocols and sterols in the virgin oil, together with its higher free fatty acid content when compared to the refined one, result in a lower oxidative stability. This is deduced from faster degradation of acyl groups and earlier generation of hydroperoxides, epoxides, and aldehydes in the virgin oil. These findings reveal that commercial virgin soybean oil quality is not necessarily higher than that of the refined type, and that a simple and rapid analysis of oil minor components by DI-SPME-GC/MS would enable one to establish quality levels within oils originating from the same plant species and similar unsaturation level regarding composition in potentially bioactive compounds and oxidative stability.
Highlights
It is known that the oxidative stability of oils depends on their unsaturation degree, determined by their acyl group profile [1], and on their composition in minor components [2,3]
Bearing in mind that oil refining processes can reduce the concentration of minor components like tocopherols, carotenoids, or free fatty acids [8], it is possible to find commercial vegetable oils originating from the same plant species with very similar compositions in main components but which differ in minor ones
Composition in Main Components Determined by 1 H-nuclear magnetic resonance (NMR)
Summary
It is known that the oxidative stability of oils depends on their unsaturation degree, determined by their acyl group profile [1], and on their composition in minor components [2,3] These minor oil components include several types of compounds with attributed antioxidant ability like tocopherols and tocotrienols, squalene, sterols, or cyclic dipeptides [4,5,6,7], and other compounds reported to increase the susceptibility of oils to oxidation, such as free fatty acids [2]. The possibility of considering the minor component profile as an indicator of the oxidative stability of edible oils seems to have been little exploited Regarding this issue, some studies have been conducted in recent years aimed at finding relationships between the composition of a wide range of vegetable oils and their resistance to oxidation [9,10,11,12,13,14]. In two of them [13,14], the composition in main components was not analyzed, even though this affects the oxidative stability of oils [1]
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