# Assessment of Soybean Oil Oxidative Stability from Rapid Analysis of its Minor Component Profile
## 1 Introduction  
It is known that the oxidative stability of oils depends on their unsaturation degree, determined by their acyl group profile [1], but also on their composition in minor components [2; 3]. These minor oil components include several types of compounds with attributed antioxidant ability like tocopherols and toctorienols, squalene, sterols, or cyclic dipeptides [4; 5; 6; 7], but also other compounds reported to increase the susceptibility of oils to oxidation, such as free fatty acids [2]. In this context, it must be noticed that although most seed oils are usually subjected to a refining process, some can also be consumed without being refined, which is to say as either virgin or cold-pressed oils. Therefore, 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 (acyl groups) but which differ in minor ones. Despite this, 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 these works, in general, attention is paid to both fatty acid composition and minor components like polyphenols, sterols, tools, \(\beta\)-carotene, lutein, or chlorophyll. However, in two of them [13; 14], the composition in main components was not analyzed, even though this also affects the oxidative stability of oils [1]. Another subject that should be taken into account when analyzing the conclusions drawn from the aforementioned studies is the selection of the Rancimat test, performed at temperatures of either 110 or 120 \({}^{\circ}\)C, to assess oil oxidative stability. Thus, although according to [PERSON] and [PERSON] [15], it can be useful to act as a \"screening\" test to identify oils with lower stability under frying conditions, the only oxidation products considered are volatile organic acids; this represents an extreme over-simplification of the oxidation process, during which myriads of compounds, many of them non-volatile, can be generated [16]. Moreover, when performing oxidative stability tests at high temperatures, it must also be taken into account that the reactions occurring under these conditions are different from those occurring at lower temperatures [3], such as during the storage of oils, and that the effect of antioxidants can also vary depending on temperature [17]. Indeed, measurement of the induction period using a Rancimat apparatus led to surprising conclusions concerning the stability of corn and soybean oils [11], which was reported to be similar to that found by other researchers for cold-pressed olive oil [18], even though the oxidative stability of the latter has been shown to be considerably higher than that of the former, both under accelerated storage conditions [19; 20] and at frying temperatures [21]. In light of all the above, this work aimed to study the influence of the composition in minor components of two commercially available soybean oils, one virgin and the other refined, on their oxidative stability under accelerated storage conditions considering the whole oxidation process. The composition in acyl groups and the unsaturation degree of the two selected oils were analyzed by \({}^{1}\)H nuclear magnetic resonance (\({}^{1}\)H-NMR), while the study of the minor oil component profile was accomplished by means of direct immersion solid-phase microextraction followed by gas chromatography/mass spectrometry (DI-SPME-GC/MS).