Formation of triacylglycerol core aldehydes during rapid oxidation of corn and sunflower oils with tert-butyl hydroperoxide/Fe2+

Effects of amino acids on the formation and distribution of glycerol core aldehydes during deep frying

Glyceryl core aldehyde (GCAs) are hazard factors produced during the frying process using oils and fats, and GCAs control and mitigation research is very important. This study investigated the effects of adding amino acids (methionine, glycine, and histidine) at 2.5, 5, and 10 mM on the formation and distribution of four GCAs during frying. High oleic sunflower oil (HOSO) was selected as frying oil for French fries. After 12 h of frying, the content of GCAs in the tert-butylhydroquinone-treated group (0.02 wt%, 1.1 mM) decreased by 29 % compared with the control group. The addition of methionine, glycine, and histidine decreased the total GCAs by 51 %, 28 %, and 27 %, respectively. The total GCAs content was best inhibited by methionine, while glycine and histidine were not significantly different from TBHQ. Methionine addition significantly reduced GCAs (9-oxo), GCAs (10-oxo-8), and GCAs (11-oxo-9) by 39 %, 78 %, and 80 %, respectively, while histidine was the most potent inhibitor of GCAs (8-oxo), which decreased by 40 %. Methionine also proved effective in slowing degradation of frying oil quality. These results provide a new direction for decreasing GCAs in frying systems.

Effects of temperature and ferric ion on the formation of glycerol core aldehydes during simulated frying

Glycerol core aldehydes (GCAs) are toxins widely formed in oils at high temperature. This study investigated the effects of frying time, temperature, and Fe³⁺ content on the GCAs formation in high-oleic sunflower oil. The results showed that the GCAs (8-oxo, 9-oxo, 10-oxo-8, 11-oxo-9) concentrations increased with time following the pseudo-first-order kinetics. Frying at 160 °C without Fe³⁺ and at 180 °C with 0.0005 mol·L^-1 Fe³⁺ yielded the lowest and highest total GCA content. The concentrations of GCAs (8-oxo) and GCAs (9-oxo) or GCAs (10-oxo-8) and GCAs (11-oxo-9) changed similarly with different frying temperature and Fe³⁺ concentration. The major GCAs was GCAs (9-oxo) (40-70%), which also had the highest formation rate (5.42 × 10^-4 mg·g^-1·h^-1). However, GCA (10-oxo-8) and GCAs (11-oxo-9) with similar proportion (ca. 10-20%) and GCAs (8-oxo) made up the least proportions (<10%).

Evaluation of glycerol core aldehydes formation in edible oils under restaurant deep frying

Glycerol core aldehydes (GCAs) are potentially toxic lipid oxidation products characterized by aldehydic acids bonded to glycerol via acyl groups. This study investigated the profile and change of GCAs in rapeseed oil (RO), high-oleic sunflower oil (HOSO) and cottonseed oil (CO) after frying chicken nuggets (CNs), fish nuggets (FNs) and French fries (FFs) for 60 h in real restaurant frying systems. Three GCAs (8-oxo, 9-oxo, and 10-oxo-8) were identified, with the GCAs (9-oxo) accounting for the highest value (60%), followed by GCAs (10-oxo-8) and GCAs (8-oxo). The total GCAs increased from 1.12 to 2.02 mg/g with frying time from 0 to 60 h in RO used for frying FNs. The FN frying systems produced the largest amount of GCAs, whereas the FF frying systems produced the least. RO contained more GCAs than CO and HOSO owing to its higher unsaturated fatty acid content (91.81%). Furthermore, the GCAs showed a high correlation with polymerized and oxidized products, indicating that the formation of GCAs were related to the oxidative stability of oils. These results may provide insight into the formation of GCAs and their control during frying.

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.

Use of lipidomics for analyzing glycerolipid and cholesteryl ester oxidation by gas chromatography, HPLC, and on-line MS

Various analytical techniques have been adopted for the isolation and identification of the oxolipids and for determining their functionality. Gas chromatography in combination with mass spectrometry (MS) has been specifically utilized in analysis of isoprostanes and other low molecular weight oxolipids, although it requires derivatization of the solutes. In contrast, liquid chromatography (LC) in combination with on-line MS has proven to be well suited for analysis of intact oxolipids without (or minimal) derivatization. LC-MS has also been helpful for the identification of lipidomic changes resulting from covalent binding of lipid ester core aldehydes to amino lipids, amino acids, peptides, and proteins. This chapter reviews the use of the above techniques for lipidomic analysis of the autoxidation products of cholesteryl esters and glycerolipids as practiced in the authors' laboratories.

A laser desorption ionization time-of-flight mass spectrometry investigation into triacylglycerols oxidation during thermal stressing of edible oils

Laser desorption ionization time-of-flight mass spectrometry (LDI-TOF MS) was used to characterize olive and sunflower oils before and after thermally assisted oxidation in order to develop a rapid fingerprinting method for oil that contains unchanged and oxidized components. No matrix was used to assist laser desorption, and simplified mass spectra were obtained in the mass range of interest (m/z 500-1000), where triacyl- and diacylglycerol ions were observed. Sample preparation was reduced to dissolving oil in chloroform saturated with NaCl. Sodiated triacylglycerols (TAGs), their epoxy/hydroxy and hydroperoxy derivatives, as well as TAGs with shortened chain fatty acids (beta-scission products) were clearly observed in the spectra. LDI-TOF MS rapidly provides semiquantitative information about the oxidation level of edible oil, and thus represents a very useful quality control tool.

Diet and lipoprotein oxidation: analysis of oxidized triacylglycerols in pig lipoproteins

Oxidized lipoproteins have a recognized role in atherogenesis, but molecular-level research on oxidized lipids in lipoproteins and the effect of diet on these molecules have been limited. In the present study, the effects of three sunflower seed oil diets differing in oxidation levels (PV in oils 1, 84, and 223 mequiv O2/kg) on lipoprotein lipid oxidation in growing pigs were investigated. The emphasis was on the investigation of oxidized TAG molecules found in chylomicrons and VLDL. A method based on RP-HPLC and electrospray ionization-MS was used for the analysis of oxidized TAG molecules. The baseline diene conjugation method was used for the estimation of in vivo levels of lipoprotein lipid oxidation. Several oxidized TAG structures were found in the samples. These products consisted of TAG molecules with a hydroxy, an epoxy, or a keto group attached to a FA, and of TAG molecules containing an aldehyde structure derived from a FA. The lipoprotein lipids and TAG were more oxidized in the pigs fed on the most oxidized oil compared with those fed on nonoxidized oil. Oxidation of dietary fat was reflected in the lipoprotein oxidation. New, detailed information on oxidized TAG molecules of chylomicrons and VLDL was obtained.

Structural analysis of hydroperoxy- and epoxy-triacylglycerols by liquid chromatography mass spectrometry

Oxidation of triacylglycerols (TAGs) containing oleic acid leads to the formation of several products. This study characterizes hydroperoxy- and epoxy-TAGs including their regio-isomers. For this purpose, epoxy- and hydroperoxy-TAGs, formed by oxidation of 1,2-dipalmitoyl-3-oleoyl-glycerol (PPO) and 1,3-dipalmitoyl-2-oleoyl-glycerol (POP) under air and 18O2, were analysed by reverse phase liquid chromatography-electrospray ionisation-mass spectrometry (LC-ESI-MS) using a triple quadrupole mass analyser, in positive ion mode. Post-column infusion of ammonium formiate was used to obtain intense molecular ion adducts. Pure 1,2-dipalmitoyl-3-epoxystearoyl-glycerol (PPEs) and 1,3-dipalmitoyl-2-epoxystearoyl-glycerol (PEsP), synthesized by epoxidation of the corresponding monounsaturated TAGs, were used to confirm MS/MS identification. The use of 18O2 oxidation experiments permitted unambiguous identification of MS/MS fragmentation pathways of both hydroperoxide and epoxy-TAGs. Fragmentation of hydroperoxy-TAGs are very distinct from their epoxy-TAGs homologues and consist of simultaneous losses of hydrogen peroxide (34 a.m.u.) and water (18 a.m.u.).

Tentative identification and quantification of TAG core aldehydes as dinitrophenylhydrazones in autoxidized sunflowerseed oil using reversed-phase HPLC with electrospray lonization MS

The molecular species of TAG core aldehydes (aldehydes still esterified to parent molecules) were detected and quantified in dietary-quality sunflowerseed oil autoxidized for 0-18 d at 60 degrees C in the dark. The analyses were performed by reversed-phase HPLC with UV (358 nm) absorption or light scattering and electrospray ionization-MS (ESI/MS) detection following preparation of the dinitrophenylhydrazone derivatives. Aldehyde production, as estimated by UV and ESI/MS, increased gradually over the 18-d period following a rapid initial destruction of the core aldehydes accumulated during storage of the commercial oil at 10 degrees C for 3 mon. The contents of hydroperoxides and hydroperoxide core aldehyde combinations were estimated to account for about 5% of total TAG, quantified as area in the chromatographic trace, after 18 d of autoxidation as estimated by an evaporative light scattering detector (ELSD). The major species of core aldehydes were tentatively identified as 9-oxononanoyl (70%)-, 12-oxo-9,10-epoxydodecenoyl (10%)-, and 13-oxo-9,11-tridecadienoyl (5%)-containing acylglycerols, plus smaller amounts of simple and mixed chain-length dialdehydes, and hydroxy and epoxy monoaldehyde-containing acylglycerols (15% of total). Quantitatively, the core aldehydes made up 2-12 g/kg of oil by UV detection and 2-9 g/kg of oil by ESI/MS detection, whereas the hydroperoxides measured in the unreduced state by HPLC with ELSD were estimated at 200 g/kg after 18 d of autoxidation. The major hydroperoxides of sunflowerseed oil were as previously identified.

Characterization of triacylglycerol and diacylglycerol composition of plant oils using high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry

Triacylglycerols (TGs) and diacylglycerols (DGs) in 16 plant oil samples (hazelnut, pistachio, poppy-seed, almond, palm, Brazil-nut, rapeseed, macadamia, soyabean, sunflower, linseed, Dracocephalum moldavica, evening primrose, corn, amaranth, Silybum arianum) were analyzed by HPLC-MS with atmospheric pressure chemical ionization (APCI) and UV detection at 205 nm on two Nova-Pak C18 chromatographic columns connected in series. A single chromatographic column and non-aqueous ethanol-acetonitrile gradient system was used as a compromise between the analysis time and the resolution for the characterization of TG composition of five plant oils. APCI mass spectra were applied for the identification of all TGs and other acylglycerols. The isobaric positional isomers can be distinguished on the basis of different relative abundances of the fragment ions formed by preferred losses of the fatty acid from sn-1(3) positions compared to the sn-2 position. Excellent chromatographic resolution and broad retention window together with APCI mass spectra enabled positive identification of TGs containing fatty acids with odd numbers of carbon atoms such as margaric (C17:0) and heptadecanoic (C17:1) acids. The general fragmentation patterns of TGs in both APCI and electrospray ionization mass spectra were proposed on the basis of MSn spectra measured with an ion trap analyzer. The relative concentrations of particular TGs in the analyzed plant oils were estimated on the basis of relative peak areas measured with UV detection at 205 nm.

Oxidized fats in foods

PURPOSE OF REVIEW

Lipid oxidation is the cause of important deteriorative changes in chemical, sensory and nutritional food properties. In particular, the question of whether oxidized fats in the diet may be detrimental to health is nowadays of the upmost concern, but finding an answer is not easy and requires careful consideration of different aspects of lipid oxidation.

RECENT FINDINGS

In this review, the most recent works on the formation, nature and evaluation of oxidized dietary lipids are addressed; important issues such as the difficulties encountered in estimating their intake and the relationships between oxidants and antioxidants in the diet are discussed, and the latest studies on health implications of oxidized lipids are summarized.

SUMMARY

The current literature reflects various important points. At present, there is no information on the intake of oxidized fats, which is essential to know if the amount of oxidized lipids in normal diets is sufficient to cause the physiological effects claimed. Recently, relevant advances in analytical methodologies for quantitation of specific oxidation compounds have been reported, although their application to improve the analytical definition of the oxidized substrate used in nutritional studies is still a goal to be reached. Alternatively, one of the most promising current tendencies in this field is the study of the molecular targets by which dietary oxidized lipids can influence health. Overall, more selected research based on coordinated multidisciplinary studies is needed to define the role of dietary oxidized fats in health.