Analysis of isomeric forms of oxidized triacylglycerols using ultra-high-performance liquid chromatography and tandem mass spectrometry

Antioxidative Effect of Dihydrosphingosine (d18:0) and α-Tocopherol on Tridocosahexaenoin (DHA-TAG)

Sphingoid bases have shown promise as effective antioxidants in fish oils together with α-tocopherol, and the effect has been attributed to products resulting from amino-carbonyl reactions (lipation products) between the sphingoid base amine group and carbonyl compounds from lipid oxidation. In this study, the synergistic effect of dihydrosphingosine (d18:0) and α-tocopherol was studied on pure docosahexaenoic acid (DHA) triacylglycerols with an omics-type liquid- and gas-chromatographic mass spectrometric approach to verify the synergistic effect, to get a comprehensive view on the effect of d18:0 on the oxidation pattern, and to identify the lipation products. The results confirmed that d18:0 rapidly reacts further in the presence of lipid oxidation products and α-tocopherol. α-Tocopherol and d18:0 showed an improved antioxidative effect after 12 h of oxidation, indicating the formation of antioxidants through carbonyl-amine reactions. Imines formed from the carbonyls and d18:0 could be tentatively identified.

Analysis of docosahexaenoic acid hydroperoxide isomers in mackerel using liquid chromatography-mass spectrometry

Docosahexaenoic acid (DHA) is mostly esterified in food and is easily oxidized by exposure to heat or light. Hydroperoxide positions of DHA mono-hydroperoxide (DHA;OOH) provide information on oxidation mechanisms (e.g., radical- or singlet oxygen oxidation), yet direct identification of esterified DHA;OOH isomers has not been achieved. We previously accomplished the direct analysis of free DHA;OOH isomers with liquid chromatography-mass spectrometry (LC-MS/MS). In this study, we developed an LC-MS/MS method for direct analysis of esterified DHA;OOH based on our previous study. The developed method was capable of distinguishing esterified DHA;OOH isomers in raw- and oxidized mackerel. The result suggested that radical oxidation of esterified DHA can progress even in refrigeration. Different transitions were observed depending on the oxidation mechanism and lipid class. The analytical method and insights obtained in this study would be valuable to further understand and effectively prevent DHA oxidation in food products.

Chemistry and liquid chromatography methods for the analyses of primary oxidation products of triacylglycerols

Triacylglycerols (TAGs) are one of the major components of the cells in higher biological systems, which can act as an energy reservoir in the living cells. The unsaturated fatty acid moiety is the key site of oxidation and formation of oxidation compounds. The TAG free radical generates several primary oxidation compounds. These include hydroperoxides, hydroxides, epidioxides, hydroperoxy epidioxides, hydroxyl epidioxides, and epoxides. The presence of these oxidized TAGs in the cell increases the chances of several detrimental processes. For this purpose, several liquid chromatography (LC) methods were reported in their analyses. This review is therefore focused on the chemistry, oxidation, extraction, and the LC methods reported in the analyses of oxidized TAGs. The studies on thin-layer chromatography were mostly focused on the total oxidized TAGs separation and employ hexane as major solvent. High-performance LC (HPLC) methods were discussed in details along with their merits and demerits. It was found that most of the HPLC methods employed isocratic elution with methanol and acetonitrile as major solvents with an ultraviolet detector. The coupling of HPLC with mass spectrometry (MS) highly increases the efficiency of analysis as well as enables reliable structural elucidation. The use of MS was found to be helpful in studying the oxidation chemistry of TAGs and needs to be extended to the complex biological systems.