A Dual Perspective of the Action of Lysine on Soybean Oil Oxidation Process Obtained by Combining 1H NMR and LC–MS: Antioxidant Effect and Generation of Lysine–Aldehyde Adducts

Abstract

Little is still known about both the effect of amino acids on the oxidation course of edible oils and the modifications that the former may undergo during this process. Bearing this in mind, the objective of this work was to study the evolution of a system consisting of soybean oil with 2% of l-lysine under heating at 70 °C and stirring conditions, analyzing how the co-oxidation of the oil and of the amino acid affects their respective evolutions, and trying to obtain information about the action mechanism of lysine on soybean oil oxidation. The study of the oil progress by 1H Nuclear Magnetic Resonance (1H NMR) showed that the presence of lysine noticeably delays oil degradation and oxidation products generation in comparison with a reference oil without lysine. Regarding lysine evolution, the analysis by 1H NMR and Liquid Chromatography–Mass Spectrometry of a series of aqueous extracts obtained from the oil containing lysine over time revealed the formation of lysine adducts, most of them at the ε position, with n-alkanals, malondialdehyde, (E)-2-alkenals, and toxic oxygenated α β-unsaturated aldehydes. However, this latter finding does not seem enough to explain the antioxidant action of lysine.

The Influence of Flaxseed Oil Cake Extract on Oxidative Stability of Microencapsulated Flaxseed Oil in Spray-Dried Powders

“…The effect of amino acids on the oxidation of edible oils is still not well described. Oxidation of proteins included in product might lead to degradation of the polypeptide chain and to formation of cross-linked protein aggregates [ 63 ]. Additionally, the functional groups of proteins can react with components from the lipid oxidation process, such as hydroperoxides or aldehydes.…”

“…Many authors reported several mechanisms of antioxidant activities of free amino acids which migrated to oil. These mechanisms include different processes, such as synergism with tocopherols, increase of radical scavenging ability, chelation of metals, and antioxidant activity of substances produced by reactions between amino acids and oxidized lipids, but these mechanisms are uncertain at this moment [ 63 , 64 ]. Additionally, the aim of the used protein mixes with polysaccharides in the case of oil encapsulation is the formation of Maillard conjugates which exhibit antioxidant mechanisms.…”

“…These amino acids can result in scavenging of free radicals and reduction of oxidation rate through electron or proton-donating ability [ 68 , 69 ]. For instance, Martin-Rubio et al [ 63 ] reported the ability of methionine to reduce lipid hydroperoxides to hydroxides. Spray drying is known to induce thermal denaturation of proteins and their partial degradation, resulting in change protein–protein hydrophobic, electrostatic, hydrogen-bonding, and disulfide-sulfhydryl interactions, which may affect the antioxidant activity of protein-rich extracts [ 20 , 70 , 71 ].…”

A Global Study by 1H NMR Spectroscopy and SPME-GC/MS of the in Vitro Digestion of Virgin Flaxseed Oil Enriched or not with Mono-, Di- or Tri-Phenolic Derivatives. Antioxidant Efficiency of These Compounds

“…However, it was noticeable that even in the more gamma-tocopherol enriched samples, having important concentrations of this compound that did not degrade, a small oxidation degree took place, as shown before. 0.95 ± 0.03 0.58 ± 0.02 DFγT 3 11.41 ± 0.29 0.78 ± 0.02 DFγT 4 28.73 ± 0.27 0.86 ± 0.01…”

“…A common strategy to avoid oxidation consists of the incorporation of compounds with antioxidant abilities in foods. Many studies have been published on the incorporation of antioxidants in lipid foods, and have evaluated their antioxidant efficiency under different processing conditions [3][4][5].…”