# Assessment of Soybean Oil Oxidative Stability from Rapid Analysis of its Minor Component Profile
## 2 Results and Discussion
### Study by \({}^{1}\)H-NMR of the Evolution Under AS Conditions of VSO and RSO
#### 2.2.2 Formation and Evolution of Oxidation Products  
* Hydroperoxides giving signal between 8.3 and 9 ppm, and their associated conjugated (Z,\(E\))- and (\(E\),\(E\))-dienes  
The evolution of the concentration of total hydroperoxides, expressed in millimoles per mole of triglyceride (mmol/mol TG), can be estimated from signal \"a\" (see Table S2 and Figure 2) and is shown in Figure 3B. The first noticeable feature is that in VSO, hydroperoxides were already detectable after the first day under AS conditions, while in RSO these products were not observed until day 3, indicating lower oxidative stability of the virgin oil. In line with acyl group evolution, the hydroperoxide concentration increased slowly over 4 and 6 days in VSO and RSO, respectively, but then the growing rate became much higher until the maximum was reached after 6 days in VSO and 8 days in RSO. All this confirms that oxidation proceeds faster in VSO than in RSO. Hydroperoxides generated in oils under AS conditions usually support conjugated diene systems with either (Z,\(E\))- or (\(E\),\(E\))-isomerism, which can be monitored separately by measuring their corresponding signals (see Table S2, signals \"b\" and \"c\", respectively). The evolution of these signals throughout the AS process can be observed in Figure 2, while the progress of their estimated concentrations in the two studied oils is shown in Figure 3B. The latter reveals that, in line with the total hydroperoxide evolution, the emergence of both types of hydroperoxy-dienes occurs earlier in VSO than in RSO; notwithstanding, their progress over time exhibits the same trend in both oils. Figure 2: \({}^{1}\)H-NMR spectrum of sample RSO before being subjected to the AS process, together with the enlargements of some spectral regions where changes occur throughout time. Letters agree with those in Table S2 (Supplementary Material), considering that “e” includes signals “e1–e6”, “f” signals “f1–f3”, and “h” signals “h1+h2”. The plots corresponding to the same \({}^{1}\)H-NMR spectral region are presented at a fixed value of absolute intensity, for them to be valid for comparative purposes. “sb”: side band of the _bis_-allylic protons signals (H+G). * Epoxides  
Epoxides constitute a relevant group of secondary lipid oxidation products, due to their notable concentration and to their potential toxicity and other adverse effects [31], despite which they have received little attention in oxidation studies. Table S2, which compiles some of these compounds, shows that only some of them, like (_E_)-epoxystearates (letter \"d\") or (_E_)-epoxy-keto-enes (letters \"g\" and \"h\"), generate signals isolated from those of the rest of epoxides. However, an estimation of their overall amount can be made, which can be useful to assess the contribution of this type of oxidation product to the total compounds generated. The evolution of their corresponding signals with time can be observed in Figure 2 (letters \"d\", \"e\", \"f\", \"g\", and \"h\"), while the progress of their estimated concentrations throughout the AS process is displayed in Figure 4, in mmol/mol TG. As pointed out in the Supplementary Material, most of the epoxides considered, designated as \"major epoxides\", give their signals between 2.87 and 3.17 ppm approximately (see Table S2 and Figure 2). According to the data in Table S2, they are supposed to include (_Z_)-epoxystearates derived from oleic groups, as well as different types of epoxy-compounds coming from polyunsaturated groups, some of them supporting other functional groups like, for example, hydroperoxy- or hydroxy-ones. Figure 3: Evolution throughout the AS process in VSO and RSO of: (**A**) the molar percentages of linolenic, linoleic, and diunsaturated \(\omega\)-6, monounsaturated, and saturated+modified acyl groups; and (**B**) the concentrations, in mmol/mol TG (triglycerides), of hydroperoxides and of their associated conjugated (_Z_,_E_)- and (_E_,_E_)-dienes. All the figures reported are mean values corresponding to 2 replicates.