A Rapid Analysis of Soybean Oil Minor Component Profile as a Tool to Predict Its Oxidative Stability: A Comprehensive View

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 oxidation products in the virgin oil. These latter include a broad variety of compounds, some of them detected for the first time in the oxidation process of soybean oil, like mono- and di-hydroperoxides, monohydroxy-conjugated dienes, epoxides, monoketo-conjugated dienes, di-or poly-hydroxy-compounds, formic acid, formates or poly-formates, compounds with 5-alkyl-(5H)-furan-2-one structure and aldehydes. 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.