Oxylipins Associated to Current Diseases Detected for the First Time in the Oxidation of Corn Oil as a Model System of Oils Rich in Omega-6 Polyunsaturated Groups. A Global, Broad and in-Depth Study by 1H NMR Spectroscopy

Abstract

For the first time, an important number of oxylipins have been identified and quantified in corn oil submitted to mild oxidative conditions at each time of their oxidation process. This oil can be considered as a model system of edible oils rich in polyunsaturated omega-6 groups. The study was carried out using 1H nuclear magnetic resonance spectroscopy (1H NMR), which does not require chemical modification of the sample. These newly detected oxylipins include dihydroperoxy-non-conjugated-dienes, hydroperoxy-epoxy-, hydroxy-epoxy- and keto-epoxy-monoenes as well as E-epoxy-monoenes, some of which have been associated with several diseases. Furthermore, the formation of other functional groups such as poly-formates, poly-hydroxy and poly-ether groups has also been proven. These are responsible for the polymerization and increased viscosity of the oil. Simultaneously, monitoring of the formation of well-known oxylipins, such as hydroperoxy-, hydroxy-, and keto-dienes, and of different kinds of oxygenated-alpha,beta-unsaturated aldehydes such as 4-hydroperoxy-, 4-hydroxy-, 4-oxo-2E-nonenal and 4,5-epoxy-2E-decenal, which are also related to different degenerative diseases, has been carried out. The provided data regarding the compounds identification and their sequence and kinetics of formation constitute valuable information for future studies in which lipid oxidation is involved, both in food and in other scientific fields.

1H NMR Study of the In Vitro Digestion of Highly Oxidized Soybean Oil and the Effect of the Presence of Ovalbumin

“…In order to select the most appropriate values to obtain accurate quantitative results in the smallest possible period of time, a broad range of recycling times and relaxation delays were tested in the acquisition of the 1 H NMR spectra. In this way, the acquisition parameters finally used were: spectral width 6410 Hz, relaxation delay 3 s, number of scans 64, acquisition time 4.819 s and pulse width 90°, in agreement with previous studies on edible oils and fats carried out in our laboratory [ 24 , 38 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ]. The relaxation delay and acquisition time used allow the complete relaxation of the protons, the signal areas thus being proportional to the number of protons that generate them, being possible their use for quantitative purposes.…”

“…However, lipid samples can also contain minor components, either natural or formed in lipid degradation processes. If these are in enough concentration to be detected by 1 H NMR, their concentration in the sample can also be determined, provided that some of their signals do not overlap with other ones [ 24 , 47 ]. This determination can be made either by adding a standard compound or by using certain compounds or structures present in the sample as reference.…”

“…In previous studies we have taken as standard reference the non-deuterated chloroform that always accompanies the deuterated chloroform [ 47 , 49 ], but its high volatility is a great inconvenient for the repeatability of the experiments. For this reason, references such as either triglycerides [ 24 , 51 ] or the total fatty acids (FA) plus fatty acyl groups (AG) [ 15 , 38 ] present in the sample have been used to quantify minor components in mmol in relation to these references given in mol. In this study, the determination of the concentration of minor components in the samples before digestion and in their digestates, was made by using the total concentration of fatty acyl groups plus fatty acids as reference.…”

“…This is the case of oxygenated α,β-unsaturated aldehydes [ 18 ], certain monoepoxides coming from different fatty acyl groups [ 19 , 20 ], keto-epoxy-monoene-derivatives [ 21 , 22 ] or certain dihydroxy-derivatives coming from linoleic groups [ 23 ], among others. All of them have been proved recently to be generated during the oxidation of an edible oil under accelerated storage conditions [ 24 ], so they could also be present in dietary oxidized lipids. Therefore, depending on their evolution during digestion, oxidation products could react with different biological components of the gastrointestinal tract, especially of the mucosa [ 25 ], and also be absorbed, thus reaching different targets.…”

Assessment of Soybean Oil Oxidative Stability from Rapid Analysis of its Minor Component Profile

“…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.…”