Detection of aldehydes and their conjugated hydroperoxydiene precursors in thermally-stressed culinary oils and fats: investigations using high resolution proton NMR spectroscopy

Effectiveness of different antioxidants in suppressing the evolution of thermally induced peroxidation products in hemp seed oil

Several scientific studies have warned that the ingestion of dietary lipid oxidation products (LOPs) may initiate or exacerbate the development of several chronic non-communicable diseases in humans. Indeed, the constantly increasing consumption of culinary oils by larger global populations indicates the need for scientific techniques to suppress the evolution of LOPs in thermo-oxidised oils. This study employed a 600.13 MHz frequency NMR spectrometer in evaluating the effect of 10, 50, and 100 ppm concentrations of chemical compounds reported to have antioxidant properties in continuously-stirred and thermally stressed polyunsaturated fatty acid (PUFA)-rich hemp seed oil at a frying temperature of 180℃ for 180 min. Research data acquired showed that the antioxidants α- and γ-tocopherol, γ-oryzanol, β-carotene, eugenol, resveratrol, ascorbyl palmitate, gentisic acid, and L-ascorbic acid all played a vital role in suppressing the evolution of secondary aldehydic lipid oxidation products in hemp seed oil. However, the most ineffective LOP-suppressing agent was L-lysine, an observation which may be accountable by its poor oil solubility. Nonetheless, trends deduced for compounds acting as antioxidants were mainly unique for each class of agent tested. Conversely, the antioxidant capacity of resveratrol was consistently higher, and this effect was found to be independent of its added amounts. This report provides a direct approach in developing scientific methods for the suppression of LOPs in thermo-oxidatively susceptible PUFA-rich cooking oils.

Low-Field Benchtop NMR Spectroscopy for Quantification of Aldehydic Lipid Oxidation Products in Culinary Oils during Shallow Frying Episodes

Introduction: Toxic aldehydic lipid oxidation products (LOPs) arise from the thermo-oxidative deterioration of unsaturated fatty acids present in heated culinary oils when exposed to high-temperature frying episodes, and currently these effects represent a major public health concern. Objectives: In this study, we investigated the applications of low-field (LF), benchtop NMR analysis to detect and quantify toxic aldehyde species in culinary oils following their exposure to laboratory-simulated shallow frying episodes (LSSFEs) at 180 °C. Four culinary oils of variable fatty acid (FA) composition were investigated to determine the analytical capabilities of the LF NMR instrument. Oil samples were also analysed using a medium-field (400 MHz) NMR facility for comparative purposes. Results: Aldehydes were quantified as total saturated and total α,β-unsaturated classes. The time-dependent production of α,β-unsaturated aldehydes decreased in the order chia > rapeseed ≈ soybean > olive oils, as might be expected from their polyunsaturated and monounsaturated FA (PUFA and MUFA, respectively) contents. A similar but inequivalent trend was found for saturated aldehyde concentrations. These data strongly correlated with medium-field 1H NMR data obtained, although LF-determined levels were significantly lower in view of its inability to detect or quantify the more minor oxygenated aldehydic LOPs present. Lower limit of detection (LLOD) values for this spectrometer were 0.19 and 0.18 mmol/mol FA for n-hexanal and trans-2-octenal, respectively. Aldehydic lipid hydroperoxide precursors of aldehydic LOPs were also detectable in LF spectra. Conclusions: We therefore conclude that there is scope for application of these smaller, near-portable NMR facilities for commercial or ‘on-site’ quality control determination of toxic aldehydic LOPs in thermally stressed frying oils.

Updates and Original Case Studies Focused on the NMR-Linked Metabolomics Analysis of Human Oral Fluids Part II: Applications to the Diagnosis and Prognostic Monitoring of Oral and Systemic Cancers

Human saliva offers many advantages over other biofluids regarding its use and value as a bioanalytical medium for the identification and prognostic monitoring of human diseases, mainly because its collection is largely non-invasive, is relatively cheap, and does not require any major clinical supervision, nor supervisory input. Indeed, participants donating this biofluid for such purposes, including the identification, validation and quantification of surrogate biomarkers, may easily self-collect such samples in their homes following the provision of full collection details to them by researchers. In this report, the authors have focused on the applications of metabolomics technologies to the diagnosis and progressive severity monitoring of human cancer conditions, firstly oral cancers (e.g., oral cavity squamous cell carcinoma), and secondly extra-oral (systemic) cancers such as lung, breast and prostate cancers. For each publication reviewed, the authors provide a detailed evaluation and critical appraisal of the experimental design, sample size, ease of sample collection (usually but not exclusively as whole mouth saliva (WMS)), their transport, length of storage and preparation for analysis. Moreover, recommended protocols for the optimisation of NMR pulse sequences for analysis, along with the application of methods and techniques for verifying and resonance assignments and validating the quantification of biomolecules responsible, are critically considered. In view of the authors’ specialisms and research interests, the majority of these investigations were conducted using NMR-based metabolomics techniques. The extension of these studies to determinations of metabolic pathways which have been pathologically disturbed in these diseases is also assessed here and reviewed. Where available, data for the monitoring of patients’ responses to chemotherapeutic treatments, and in one case, radiotherapy, are also evaluated herein. Additionally, a novel case study featured evaluates the molecular nature, levels and diagnostic potential of ¹H NMR-detectable salivary ‘acute-phase’ glycoprotein carbohydrate side chains, and/or their monomeric saccharide derivatives, as biomarkers for cancer and inflammatory conditions.

Nuclear Magnetic Resonance Spectroscopic Analysis of the Evolution of Peroxidation Products Arising from Culinary Oils Exposed to Thermal Oxidation: An Investigation Employing 1H and 1H-1H COSY and TOCSY Techniques

Scientific warnings on the deleterious health effects exerted by dietary lipid oxidation products (LOPs) present in thermally stressed culinary oils have, to date, not received adequate attention given that there has been an increase in the use and consumption of such oil products in everyday life. In this study, high-resolution ¹H nuclear magnetic resonance (NMR) analysis was used to characterize and map chemical modifications to fatty acid (FA) acyl groups and the evolution of LOPs in saturated fatty acid (SFA)-rich ghee, monounsaturated fatty acid (MUFA)-rich groundnut, extra virgin olive, and macadamia oils, along with polyunsaturated fatty acid (PUFA)-rich sesame, corn and walnut oils, which were all thermally stressed at 180 °C, continuously and discontinuously for 300 and 480 min, respectively. Results acquired revealed that PUFA-rich culinary oils were more susceptible to thermo-oxidative stress than the others tested, as expected. However, ghee and macadamia oil both generated only low levels of toxic LOPs, and these results demonstrated a striking similarity. Furthermore, at the 120 min thermo-oxidation time-point, the discontinuous thermo-oxidation episodes produced higher concentrations of aldehydic LOPs than those produced during continuous thermo-oxidation sessions for the same duration. On completion of the thermo-oxidation period, a higher level of triacylglycerol chain degradation, and hence, higher concentrations of aldehydes, were registered in culinary oils thermally stressed continuously over those found in discontinuous thermo-oxidized oils. These findings may be crucial in setting targets and developing scientific methods for the suppression of LOPs in thermo-oxidized oils.

Analytical and Structural Tools of Lipid Hydroperoxides: Present State and Future Perspectives

Mono- and polyunsaturated lipids are particularly susceptible to peroxidation, which results in the formation of lipid hydroperoxides (LOOHs) as primary nonradical-reaction products. LOOHs may undergo degradation to various products that have been implicated in vital biological reactions, and thus in the pathogenesis of various diseases. The structure elucidation and qualitative and quantitative analysis of lipid hydroperoxides are therefore of great importance. The objectives of the present review are to provide a critical analysis of various methods that have been widely applied, and more specifically on volumetric methods, applications of UV-visible, infrared, Raman/surface-enhanced Raman, fluorescence and chemiluminescence spectroscopies, chromatographic methods, hyphenated MS techniques, NMR and chromatographic methods, NMR spectroscopy in mixture analysis, structural investigations based on quantum chemical calculations of NMR parameters, applications in living cells, and metabolomics. Emphasis will be given to analytical and structural methods that can contribute significantly to the molecular basis of the chemical process involved in the formation of lipid hydroperoxides without the need for the isolation of the individual components. Furthermore, future developments in the field will be discussed.

Evidence-Based Challenges to the Continued Recommendation and Use of Peroxidatively-Susceptible Polyunsaturated Fatty Acid-Rich Culinary Oils for High-Temperature Frying Practises: Experimental Revelations Focused on Toxic Aldehydic Lipid Oxidation Products

In this manuscript, a series of research reports focused on dietary lipid oxidation products (LOPs), their toxicities and adverse health effects are critically reviewed in order to present a challenge to the mindset supporting, or strongly supporting, the notion that polyunsaturated fatty acid-laden frying oils are "safe" to use for high-temperature frying practises. The generation, physiological fates, and toxicities of less commonly known or documented LOPs, such as epoxy-fatty acids, are also considered. Primarily, an introduction to the sequential autocatalytic peroxidative degradation of unsaturated fatty acids (UFAs) occurring during frying episodes is described, as are the potential adverse health effects posed by the dietary consumption of aldehydic and other LOP toxins formed. In continuance, statistics on the dietary consumption of fried foods by humans are reviewed, with a special consideration of French fries. Subsequently, estimates of human dietary aldehyde intake are critically explored, which unfortunately are limited to acrolein and other lower homologues such as acetaldehyde and formaldehyde. However, a full update on estimates of quantities derived from fried food sources is provided here. Further items reviewed include the biochemical reactivities, metabolism and volatilities of aldehydic LOPs (the latter of which is of critical importance regarding the adverse health effects mediated by the inhalation of cooking/frying oil fumes); their toxicological actions, including sections focussed on governmental health authority tolerable daily intakes, delivery methods and routes employed for assessing such effects in animal model systems, along with problems encountered with the Cramer classification of such toxins. The mutagenicities, genotoxicities, and carcinogenic potential of aldehydes are then reviewed in some detail, and following this the physiological concentrations of aldehydes and their likely dietary sources are considered. Finally, conclusions from this study are drawn, with special reference to requirements for (1) the establishment of tolerable daily intake (TDI) values for a much wider range of aldehydic LOPs, and (2) the performance of future nutritional and epidemiological trials to explore associations between their dietary intake and the incidence and severity of non-communicable chronic diseases (NCDs).

The impact of partial oil substitution and trace metal ions on the evolution of peroxidation products in thermally stressed culinary oils

Suppressing toxic aldehydic lipid oxidation product (LOP) generation in culinary oils is now considered vital, since the deleterious effects arising from their ingestion are implicated in a wide range of disease conditions. Partial substitution involves the replenishment of thermally-stressed culinary oils with corresponding unheated ones. This technique was tested by employing 10%, 25%, 50%, and 75% (v/v) partial substitutions of coconut, olive, rapeseed, and sunflower oils at 180℃ for a 300 min continuous thermo-oxidation duration. Oil samples were analysed by proton nuclear magnetic resonance (¹H NMR) spectroscopy. Trace metal levels, including oxidation-reduction (redox)-active metal ions credited with enhancing cooking oil oxidation were also analysed using inductively coupled plasma-optical emission spectroscopy (ICP-OES). As expected, the degree of oil unsaturation, and the % partial substitutions significantly influenced their susceptibility to thermo-oxidation. In view of the very low polyunsaturated fatty acid (PUFA) and monounsaturated fatty acid (MUFA) contents of coconut oil, both the class and concentrations of evolved LOPs were found to be least affected by this partial substitution process. Aldehydic LOPs were greatly suppressed in partially-substituted rapeseed oil. The % suppression activity of LOPs evaluated for the partially substituted oils were generally high making partial oil substitutions an effective chemical-free method in suppressing LOPs at both industrial and commercial levels. In general, the % partial oil substitutions were directly related to the dilution effect observed for LOPs quantified in the oils. Furthermore, trace metal ion concentrations measured in the culinary oils did not influence the evolution of LOPs in the oils.

Comparative 1H NMR-Based Chemometric Evaluations of the Time-Dependent Generation of Aldehydic Lipid Oxidation Products in Culinary Oils Exposed to Laboratory-Simulated Shallow Frying Episodes: Differential Patterns Observed for Omega-3 Fatty Acid-Containing Soybean Oils

Soybean oil is the second most exported oil from the United States and South America, and is widely marketed as a cooking oil product containing numerous health benefits for human consumers. However, culinary oils with high polyunsaturated fatty acid (PUFA) contents, are known to produce high quantities of lipid oxidation products (LOPs), including toxic aldehydes upon exposure to high-temperature frying episodes. Previous studies have demonstrated causal links between aldehyde ingestion and inhalation with deleterious health perturbations, including mutagenic and carcinogenic effects, along with cardiovascular and teratogenic actions. In this study, aldehydic LOPs were detected and quantified in commercially available samples of soybean, avocado, corn and extra-virgin olive oil products before and after their exposure to laboratory-simulated laboratory frying episodes (LSSFEs) using high-resolution 1H nuclear magnetic resonance (NMR) analysis. Results acquired demonstrated that PUFA-rich soybean and corn oils gave rise to the highest concentrations of oil aldehydes from the thermo-oxidation of unsaturated fatty acids, whereas monounsaturated fatty acid (MUFA)-laden avocado and olive oils were much more resistant to this peroxidation process, as expected. Multivariate chemometrics analyses provided evidence that an orthogonal component pattern of aldehydic LOPs featuring low-molecular-mass n-alkanals such as propanal, and 4-oxo-alkanals, arises from thermo-oxidation of the ω-3 fatty acid (FA) linolenic acid (present in soybean oils at levels of ca. 7% (w/w)), was able to at least partially distinguish this oil from corresponding samples of thermally-stressed corn oil. Despite having a similar total PUFA level, corn oil has only a negligible ω-3 FA content, and therefore generated significantly lower levels of these two aldehyde classes. In view of the adverse health effects associated with dietary LOP ingestion, alternative methodologies for the incorporation of soybean oils within high-temperature frying practices are proposed.

The Role of Polydimethylsiloxane in Suppressing the Evolution of Lipid Oxidation Products in Thermo-Oxidised Sunflower Oil: Influence of Stirring Processes

Suppressing the evolution of lipid oxidation products (LOPs) in commercially available culinary oils is considered to represent a valuable health-promoting incentive since these agents have cytotoxic and genotoxic properties and have been implicated in the pathogenesis of several chronic disease states. One agent used to suppress LOPs formation is polydimethylsiloxane (PDMS). In this study, proton nuclear magnetic resonance (¹H NMR) analysis was employed to evaluating the influence of increasing PDMS concentrations (6.25 × 10⁻⁷, 1.0 × 10⁻⁵, 0.025, 0.05, 0.1, 0.5, 1.0, 5.0, and 10.0 ppm) in either stirred or unstirred refined sunflower oil exposed to thermal stressing episodes continuously at 180°C for 300 min with no oil replenishment. Results acquired showed that the extent of blockage of LOPs generation was correlated with increasing concentrations of PDMS. The minimal level of added PDMS required to provide a statistically significant protective role for both stirred and unstirred culinary oils when exposed to high frying temperatures was only 6.25 × 10⁻⁷ ppm. Furthermore, stirring at 250 rpm was experimentally determined to reduce the functional role PDMS. This is vital in a real world setting since the boiling process of frying may ultimately reduce the LOPs suppression activity of PDMS.

NMR and Computational Studies as Analytical and High-Resolution Structural Tool for Complex Hydroperoxides and Diastereomeric Endo-Hydroperoxides of Fatty Acids in Solution-Exemplified by Methyl Linolenate

A combination of selective 1D Total Correlation Spectroscopy (TOCSY) and 1H-13C Heteronuclear Multiple Bond Correlation (HMBC) NMR techniques has been employed for the identification of methyl linolenate primary oxidation products without the need for laborious isolation of the individual compounds. Complex hydroperoxides and diastereomeric endo-hydroperoxides were identified and quantified. Strongly deshielded C-O-O-H 1H-NMR resonances of diastereomeric endo-hydroperoxides in the region of 8.8 to 9.6 ppm were shown to be due to intramolecular hydrogen bonding interactions of the hydroperoxide proton with an oxygen atom of the five-member endo-peroxide ring. These strongly deshielded resonances were utilized as a new method to derive, for the first time, three-dimensional structures with an assignment of pairs of diastereomers in solution with the combined use of 1H-NMR chemical shifts, Density Functional Theory (DFT), and Our N-layered Integrated molecular Orbital and molecular Mechanics (ONIOM) calculations.

Potential Adverse Public Health Effects Afforded by the Ingestion of Dietary Lipid Oxidation Product Toxins: Significance of Fried Food Sources

Exposure of polyunsaturated fatty acid (PUFA)-rich culinary oils (COs) to high temperature frying practices generates high concentrations of cytotoxic and genotoxic lipid oxidation products (LOPs) via oxygen-fueled, recycling peroxidative bursts. These toxins, including aldehydes and epoxy-fatty acids, readily penetrate into fried foods and hence are available for human consumption; therefore, they may pose substantial health hazards. Although previous reports have claimed health benefits offered by the use of PUFA-laden COs for frying purposes, these may be erroneous in view of their failure to consider the negating adverse public health threats presented by food-transferable LOPs therein. When absorbed from the gastrointestinal (GI) system into the systemic circulation, such LOPs may significantly contribute to enhanced risks of chronic non-communicable diseases (NCDs), e.g. cancer, along with cardiovascular and neurological diseases. Herein, we provide a comprehensive rationale relating to the public health threats posed by the dietary ingestion of LOPs in fried foods. We begin with an introduction to sequential lipid peroxidation processes, describing the noxious effects of LOP toxins generated therefrom. We continue to discuss GI system interactions, the metabolism and biotransformation of primary lipid hydroperoxide LOPs and their secondary products, and the toxicological properties of these agents, prior to providing a narrative on chemically-reactive, secondary aldehydic LOPs available for human ingestion. In view of a range of previous studies focused on their deleterious health effects in animal and cellular model systems, some emphasis is placed on the physiological fate of the more prevalent and toxic α,β-unsaturated aldehydes. We conclude with a description of targeted nutritional and interventional strategies, whilst highlighting the urgent and unmet clinical need for nutritional and epidemiological trials probing relationships between the incidence of NCDs, and the frequency and estimated quantities of dietary LOP intake.

Oxidative stability of extra-virgin olive oil enriched or not with lycopene. Importance of the initial quality of the oil for its performance during in vitro gastrointestinal digestion

The performance of commercial non-enriched and lycopene-enriched extra-virgin olive oils (EVOO) during in vitro gastrointestinal digestion was studied in order to elucidate potential benefits of lycopene addition. Samples were analyzed before and after digestion by Proton Nuclear Magnetic Resonance (¹H NMR) and Solid Phase Microextraction-Gas Chromatography/Mass Spectrometry (SPME-GC/MS). EVOO samples differed in both main (oleic and linoleic acyl groups) and minor components (phenolic and oxidation compounds). Regardless of the presence of lycopene, all the samples reached a high degree of lipolysis and showed high stability towards oxidation under digestion conditions. Rather than oxidation reactions, the hydroperoxides initially present in the oil were reduced to more stable hydroxides. Likewise, hydroxy-diene isomerization from cis,trans to trans,trans occurred. Hence, the presumed antioxidant effect of lycopene was not noticed during in vitro digestion of EVOO. Similar experiments carried out with a more polyunsaturated oil (sunflower oil) indicated that lycopene slowed down the advance of oxidation slightly. However, in the case of EVOO, its initial quality prevailed over the slight antioxidant effect exerted by lycopene at the concentration present in commercial samples, determining the oxidation compound profile of the digests.

Evaluations of the Peroxidative Susceptibilities of Cod Liver Oils by a 1H NMR Analysis Strategy: Peroxidative Resistivity of a Natural Collagenous and Biogenic Amine-Rich Fermented Product

High-resolution 1H nuclear magnetic resonance (NMR) analysis was employed to molecularly screen the lipid, lipid oxidation product (LOP), and antioxidant compositions of four natural (unrefined) cod liver oil (CLO) products. Products 1-3 were non-fermented CLOs, whilst Product 4 was isolated from pre-fermented cod livers. Supporting analytical data that were acquired included biogenic amine, flavanone, tannin, phenolic antioxidant, α-tocopherol, and oxygen radical absorbance capacity (ORAC) determinations by recommended HPLC, LC/MS/MS, or spectrophotometric methods. SDS-PAGE, HPLC, and 1H NMR analyses investigated and determined collagenous antioxidants and their molecular mass ranges. 1H NMR analysis of aldehydic LOPs was employed to explore the susceptibilities/resistivities of each CLO product to peroxidation that is induced by thermal stressing episodes (TSEs) at 180°C, or following prolonged (42 day) storage episodes at 4 and 23 °C. Product 4 displayed extremely high ORAC values, which were much greater than those of Products 1-3, and that were predominantly ascribable to significant levels of peroxidation-blocking and/or aldehyde-consuming collagenous polypeptides/peptides and ammoniacal agents therein. Significantly lower levels of toxic aldehydes were generated in the pre-fermented Product 4 during exposure to TSEs, or the above long-term storage episodes. These results confirmed the enhanced peroxidative resistivity of a fermented, antioxidant-fortified natural CLO product over those of non-fermented unrefined products. Product 4: Green Pasture Blue Ice™ Fermented Cod Liver Oil.

Evaluation of antioxidant properties of the different tissues of vine tea (Ampelopsis grossedentata) in stripped canola oil and sunflower oil

The leaves of Ampelopsis grossedentata have a long history of use as a health tea and herbal medicine. Data on the distribution of active metabolites in, and antioxidant capacities of, different vine tea tissues remain incomplete. The aim of this work was to investigate the content of metabolites from A. grossedentata different tissues and evaluate the antioxidant capacities of the extraction of the species in vitro and in oil systems: canola oil and sunflower oil. To evaluate the degree of lipid oxidation, the peroxide value (POV) and thiobarbituric acid-reactive substance value (TBARS) were determined, and proton nuclear magnetic resonance (¹ H-NMR) was performed. The results revealed a high total flavonoid content in each of the four extractions (>580 mg/g dried weigh). Leaf extractions exhibited higher antioxidant ability, followed by fruit extract and butylated hydroxytoluene (BHT). The POVs of oils bearing extracts of A. grossedentata and BHT maintained less than 21.08 meq/kg oil against to control with 1,406.33 ± 52.63 meq/kg oil on day 32 in canola oil, and 27.87 meq/kg oil comparing to 1,892.96 ± 48.63 meq/kg oil in control on day 24 in sunflower oil. Concurring results were also obtained in TBARS and ¹ H-NMR analysis. Our results indicated that these different tissues of A. grossedentata could be a potential antioxidant resource, and this work may contribute to the comprehensive utilization of this species. PRACTICAL APPLICATION: Leaf extracts of Ampelopsis grossedentata showed effective antioxidant properties, followed by the fruit extract, which showed similar activity to that of the synthetic antioxidant of BHT. Moreover, the investigation of different tissues within the plant may contribute to the comprehensive utilization of this species.

1 H-13 C HMBC NMR experiments as a structural and analytical tool for the characterization of elusive trans/cis hydroperoxide isomers from oxidized unsaturated fatty acids in solution

The radical-dependent oxidation of unsaturated fatty acids is a fundamental reaction in lipid chemistry, biochemistry, and technology. We report herein the first successful application of ¹ H-¹³ C HMBC NMR experiment for the identification and quantification of complex and minor (3.9% to 0.85%) components of cis and trans primary hydroperoxide isomers of oxidized oleate and linoleate methyl esters in solution, without the need of laborious isolation of the individual components.

Toxic aldehyde generation in and food uptake from culinary oils during frying practices: peroxidative resistance of a monounsaturate-rich algae oil

Human ingestion of cytotoxic and genotoxic aldehydes potentially induces deleterious health effects, and high concentrations of these secondary lipid oxidation products (LOPs) are generated in polyunsaturated fatty acid (PUFA)-rich culinary oils during high temperature frying practices. Here, we explored the peroxidative resistance of a novel monounsaturate-rich algae frying oil (MRAFO) during laboratory-simulated shallow- and domestically-based repetitive deep-frying episodes (LSSFEs and DBRDFEs respectively), the latter featuring potato chip fryings. Culinary frying oils underwent LSSFEs at 180 °C, and DBRDFEs at 170 °C: aldehydes were determined by ¹H NMR analysis in samples collected at increasing heating/frying time-points. Fast food restaurant-fried potato chip serving (FFRPCS) aldehyde contents were also monitored. Substantially lower levels of aldehydes were generated in the MRAFO product than those observed in PUFA-richer oils during LSSFEs. Toxicologically-significant concentrations of aldehydes were detected in FFRPCSs, and potato chips exposed to DBRDFEs when using a PUFA-laden sunflower oil frying medium: these contents increased with augmented deep-frying episode repetition. FFRPCS aldehyde contents were 10–25 ppm for each class monitored. In conclusion, the MRAFO product generated markedly lower levels of food-penetrative, toxic aldehydes than PUFA-rich ones during LSSFEs. Since FFRPCS and DBRDFE potato chip aldehydes are predominantly frying oil-derived, PUFA-deplete MRAFOs potentially offer health-friendly advantages.

Characterisation of peroxidation products arising from culinary oils exposed to continuous and discontinuous thermal degradation processes

High-resolution NMR analysis has been used, for the first time, to identify, putatively, two new secondary aldehydic lipid oxidation products in culinary oils.

High Resolution NMR Spectroscopy as a Structural and Analytical Tool for Unsaturated Lipids in Solution

Mono- and polyunsaturated lipids are widely distributed in Nature, and are structurally and functionally a diverse class of molecules with a variety of physicochemical, biological, medicinal and nutritional properties. High resolution NMR spectroscopic techniques including 1H-, 13C- and 31P-NMR have been successfully employed as a structural and analytical tool for unsaturated lipids. The objective of this review article is to provide: (i) an overview of the critical 1H-, 13C- and 31P-NMR parameters for structural and analytical investigations; (ii) an overview of various 1D and 2D NMR techniques that have been used for resonance assignments; (iii) selected analytical and structural studies with emphasis in the identification of major and minor unsaturated fatty acids in complex lipid extracts without the need for the isolation of the individual components; (iv) selected investigations of oxidation products of lipids; (v) applications in the emerging field of lipidomics; (vi) studies of protein-lipid interactions at a molecular level; (vii) practical considerations and (viii) an overview of future developments in the field.

Polyunsaturated lipids and vitamin A oxidation during cod liver oil in vitro gastrointestinal digestion. Antioxidant effect of added BHT

The extent of cod liver oil hydrolysis and oxidation during in vitro gastrointestinal digestion was investigated by Proton Nuclear Magnetic Resonance (¹H NMR) and Solid Phase Microextraction-Gas Chromatography/Mass Spectrometry (SPME-GC/MS). These techniques evidenced the degradation of polyunsaturated ω-3 and ω-6 lipids and, for the first time, that of vitamin A, naturally present in cod liver oil. Cis,trans-conjugated dienes associated with hydroperoxides, as well as monoepoxides, cis,trans-2,4-alkadienals, 4-hydroperoxy- and 4-hydroxy-2-alkenals, and several vitamin A derived metabolites were generated. Moreover, the effect of the addition of the synthetic antioxidant 2,6-di-tert-butyl-hydroxytoluene (BHT) at 20 and 800ppm was tackled. Both techniques showed BHT to be efficient in limiting oxidation reactions during digestion, almost inhibiting them at 800ppm. Therefore, the simultaneous intake of antioxidants with cod liver oil should be considered, in order to increase polyunsaturated lipid and vitamin A bioaccessibility and avoid formation of toxic oxidation compounds like oxygenated alpha,beta-unsaturated aldehydes.

Effects of Caffeic Acid Phenethyl Ester and 4-Vinylcatechol on the Stabilities of Oil-in-Water Emulsions of Stripped Soybean Oil

Caffeic acid phenethyl ester (CAPE) and 4-vinylcatechol (4-VC) were prepared for studying their antioxidative activities in emulsion. Oil-in-water emulsions of stripped soybean oil containing 200 ppm of CAPE, 4-VC, or α-tocopherol were stored at 40 °C in the dark for 50 days, and proton nuclear magnetic resonance ((1)H NMR) was used to identify and quantify the oxidation products. Emulsion droplet sizes, peroxide values, and levels of primary oxidation products (i.e., hydroperoxides) and secondary oxidation products (i.e., aldehydes) were determined. The results showed that CAPE (200 ppm) and 4-VC (200 ppm) had significantly greater antioxidant activities on the oxidation of stripped soybean oil-in-water emulsions than α-tocopherol (200 ppm). The peroxide values of CAPE (8.4 mequiv/L emulsion) and 4-VC (15.0 mequiv/L emulsion) were significantly lower than that of α-tocopherol (33.4 mequiv/L emulsion) (p < 0.05) on 36 days. In addition, the combinations of CAPE + α-tocopherol (100 + 100 ppm) or 4-VC + α-tocopherol (100 + 100 ppm) had better antioxidant activities than α-tocopherol (200 ppm). For CAPE + α-tocopherol, 4-VC + α-tocopherol, and α-tocopherol, the amounts of conjugated diene forms were 16.67, 13.72, and 16.32 mmol/L emulsion, and the concentrations of aldehydes were 2.15, 1.13, and 4.26 mmol/L emulsion, respectively, after 50 days of storage.

Lipid peroxidation in culinary oils subjected to thermal stress

The levels of cytotoxic aldehydic products in different culinary oils, with or without thermal stress, (routine domestic or commercial frying) were determined by thiobarbituric acid method. The results showed that (i) thiobarbituric acid reactivity was much higher in edible oils rich in polyunsaturated fatty acids than those rich in saturated fatty acids or monounsaturated fatty acids, even without thermal stress, (ii) the lipid peroxide levels were in proportion to the duration of thermal stress, (iii) nature of the container used (steel, iron or teflon-coated) had no significant effect on the extent of lipid peroxidation under identical conditions of thermal stress and (iv) thermally stressed oils collected from hotels and roadside caterers contained higher levels of cytotoxic aldehydic products, when compared to oils thermally stressed under domestic frying conditions. These results suggest that dietary ingestion of thermally or autoxidatively stressed polyunsaturated fatty acid rich culinary oils is more harmful compared with those similarly treated oils rich in saturated fatty acids and monounsaturated fatty acids.

Study of the heat stability of sunflower oil enriched in natural antioxidants by different analytical techniques and front-face fluorescence spectroscopy combined with Independent Components Analysis

The aim of this study was to find objective analytical methods to study the degradation of edible oils during heating and thus to suggest solutions to improve their stability. The efficiency of Nigella seed extract as natural antioxidant was compared with butylated hydroxytoluene (BHT) during accelerated oxidation of edible vegetable oils at 120 and 140 °C. The modifications during heating were monitored by 3D-front-face fluorescence spectroscopy along with Independent Components Analysis (ICA), (1)H NMR spectroscopy and classical physico-chemical methods such as anisidine value and viscosity. The results of the study clearly indicate that the natural seed extract at a level of 800 ppm exhibited antioxidant effects similar to those of the synthetic antioxidant BHT at a level of 200 ppm and thus contributes to an increase in the oxidative stability of the oil.

Changes in human meibum lipid composition with age using nuclear magnetic resonance spectroscopy

PURPOSE

Human tear film stability decreases with increasing age. In this study, the changes in meibum composition were measured in search of markers of tear film instability.

METHODS

(1)H NMR nuclear magnetic resonance (NMR) spectra of 43 normal donors aged 1 to 88 years were acquired.

RESULTS

Compared with meibum from adolescents and adults, meibum from infants and children contains less CH(3) and C═C groups and an increased aldehyde-to-lipid hydroperoxide ratio.

CONCLUSIONS

It is reasonable that tear film stability is higher in infants than in adults. Their meibum contains less CH(3) and C═C groups and higher levels of protein, and as a result, the lipid is more ordered because of the tighter and stronger lipid-lipid interactions. For water to evaporate, it must first pass through the tight lipid-lipid barrier. For tears to break up, lipid-lipid interactions must be broken. It is reasonable that because the lipid-lipid interactions are stronger in infants' and children's tears compared with those of adolescents and adults, the tear film in the younger groups is more stable and provides a better barrier to evaporation than does the tear film of adults. Lipid saturation could be the critical feature in meibum that stabilizes tears in infants.

Differences in human meibum lipid composition with meibomian gland dysfunction using NMR and principal component analysis

PURPOSE

Nuclear magnetic resonance (NMR) spectroscopy has been used to quantify lipid wax, cholesterol ester terpenoid and glyceride composition, saturation, oxidation, and CH₂ and CH₃ moiety distribution. This tool was used to measure changes in human meibum composition with meibomian gland dysfunction (MGD).

METHODS

(1)H-NMR spectra of meibum from 39 donors with meibomian gland dysfunction (Md) were compared to meibum from 33 normal donors (Mn).

RESULTS

Principal component analysis (PCA) was applied to the CH₂/CH₃ regions of a set of training NMR spectra of human meibum. PCA discriminated between Mn and Md with an accuracy of 86%. There was a bias toward more accurately predicting normal samples (92%) compared with predicting MGD samples (78%). When the NMR spectra of Md were compared with those of Mn, three statistically significant decreases were observed in the relative amounts of CH₃ moieties at 1.26 ppm, the products of lipid oxidation above 7 ppm, and the =CH moieties at 5.2 ppm associated with terpenoids.

CONCLUSIONS

Loss of the terpenoids could be deleterious to meibum since they exhibit a plethora of mostly positive biological functions and could account for the lower level of cholesterol esters observed in Md compared with Mn. All three changes could account for the higher degree of lipid order of Md compared with age-matched Mn. In addition to the power of NMR spectroscopy to detect differences in the composition of meibum, it is promising that NMR can be used as a diagnostic tool.

Fruit and vegetable and fried food consumption and 3-(2-deoxy-β-D-erythro-pentafuranosyl)pyrimido[1,2-α] purin-10(3H)-one deoxyguanosine adduct formation

Diet has been shown to modulate M(1)dG adduct, a biomarker of oxidative stress and lipid peroxidation. Thus, we analysed the association between diet and M(1)dG in 120 controls and 67 Map Ta Phut industrial estate workers in Rayong, Thailand, to evaluate the influence of fruit and vegetables, and fried and charcoal-grilled/barbecued food consumption on M(1)dG. M(1)dG was decreased in controls reporting to consume 14-17 servings/week of fruit and vegetables (mean ratio [MR]= 0.35, CI 0.18-0.69, p< 0.05). Conversely, a non-statistically significant M(1)dG increment was detected in controls consuming 9-18 servings/week of fried food (MR = 1.33, CI 0.88-2.00, p = 0.168). No effect of charcoal-grilled/barbecued food was found. No effect of diet was observed in workers. An association with smoking was observed in controls (MR = 1.88, CI 1.14-3.10, p < 0.05), but not in workers. M(1)dG can induce mutations and/or methylation changes within the promoter regions of cancer-related genes, thus promotion of healthy eating practices should be recommended.

Analysis of the composition of lipid in human meibum from normal infants, children, adolescents, adults, and adults with meibomian gland dysfunction using ¹H-NMR spectroscopy

PURPOSE

This study represents a first step toward the evaluation of possible compositional differences in meibum from normal donors (Mn) and donors with meibomian gland dysfunction (Md) by (1)H-NMR spectroscopy. The results highlight the applicability of (1)H-NMR spectroscopy for the quantitative analysis of waxes, cholesteryl esters, and glycerides in meibum lipid (ML).

METHODS

Meibum was obtained from 41 normal donors and 51 donors with meibomian gland dysfunction (MGD). (1)H-NMR spectroscopy was used to quantify the amount of waxes, glycerides, and cholesteryl esters in human meibum.

RESULTS

The relative amount of cholesteryl esters in Mn increased with age and was 40% (P < 0.05) lower in Md. Interestingly, the relative levels of cholesteryl esters in infant meibum were comparable to those in Md. The relative amounts of glycerides were not affected significantly by age or MGD.

CONCLUSIONS

The changes in cholesteryl ester could be used as a molecular marker for MGD and could potentially be applied to follow the efficacy of drug therapy in the treatment of MGD. The similarity of the levels of cholesteryl esters in infant meibum and Md suggests that the relative amounts of these meibum components alone are unlikely to be responsible for the increased stability of the infant tear film and decreased stability of the tear film with MGD. This study reveals the complexity of human MLs and the changes that occur with age and disease. Understanding the factors that lead to such variations is of utmost relevance in the design of effective therapies.

Effects of aldehydes on CD36 expression

INTRODUCTION

During the oil frying process lipid peroxidation compounds are formed. These products can modulate gene expression and alter cellular behaviour. The cellular uptake of oxidized LDL, a key step in the development of atherosclerosis, is mediated by the CD36 scavenger receptor, whose expression is down-regulated by alpha-tocopherol.

OBJECTIVE

To determine the effects of water-soluble aldehydes, obtained from thermally oxidized sunflower oil on the expression of CD36 scavenger receptor in human monocytes (THP-1 cells). We also wanted to study the effects of alpha-tocopherol on CD36 expression in the presence of water-soluble aldehydes.

MATERIALS AND METHODS

Sunflower oil was heated in a frying pan, at 180--200 degrees C for 40 min, water-soluble aldehydes were isolated, and the content of thiobarbituric acid reacting substances (TBARS) was determined. THP-1 monocytes were cultured in RPMI medium during 24 h and incubated with increasing concentrations of the water-soluble aldehydes (ranging from 0.05 to 1 microM) and with or without 50 microM of alpha-tocopherol. In parallel, THP-1 cells were cultured with the same volume of an extract obtained from non-oxidized oil or distilled water. The CD36 expression at the cell surface was studied with fluorescence-activated cell sorting (FACS).

RESULTS

Monocytes incubated in a medium containing water-soluble aldehydes, showed a dose dependent increase in the expression of the CD36 protein on the cell surface, compared to with the control groups. When the cells were treated simultaneously with 50 microM of alpha-tocopherol a significant reduction in the expression of the CD36 protein was observed.

CONCLUSION

Water-soluble aldehydes, extracted from thermally oxidized culinary oil, increase the expression of CD36. This effect is partially decreased by the presence of alpha-tocopherol.

Detection of primary and secondary oxidation products by Fourier transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance (NMR) in sunflower oil during storage

The oxidation of sunflower oil, stored in closed receptacles at room temperature for a period of 10 years, was monitored using Fourier transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance (NMR). The objective was to understand the evolution of the oxidation process in sunflower oil under the conditions above mentioned. These techniques provide information about the oxidative status of several oil samples and the primary and some of the secondary oxidation products formed in the oxidation process. The results obtained show that, under these conditions, sunflower oxidation takes place in a different way to that at higher temperatures with aeration. The 1H NMR spectra show that in the first oxidation stages of the process only hydroperoxides supporting cis, trans-conjugated double bonds are formed and that at more advanced stages hydroperoxides having trans, trans-conjugated double bonds are generated, with the latter always being in a smaller proportion than the former. In addition, the presence of hydroxy derivatives supporting cis, trans-conjugated double bonds among the primary oxidation compounds is shown for the first time. Also, from early oxidation stages onward and unlike the process at 70 degrees C with aeration, it is noticeable that 4-hydroxy- trans-2-alkenals are formed in much higher proportions than 4-hydroperoxy- trans-2-alkenals. This fact could be associated with the presence of hydroxy derivatives with cis, trans-conjugated double bonds among the primary oxidation products and the limited concentration of oxygen during the oxidation. Furthermore, relationships between some oxidation conditions and the oxidation level of the samples were statistically analyzed.

Clastogenic and cytotoxic effects of lipid peroxidation products generated in culinary oils submitted to thermal stress

In rats, the administration of oil submitted to high temperatures is teratogenic. To understand the mechanisms involved, the clastogenic and cytotoxic effects were studied respectively in lymphocytes, hepatocytes (HepG2) and in human umbilical vein endothelial cells (HUVEC) cultured with a water extract obtained from heated oil (HO). In lymphocytes incubated with HO containing 0.075 or 0.15 microM of thiobarbituric reacting substances, the rate of chromosomal breakage was 18.4% and 23.1%, compared to 8.7% and 6.6%, or 8.1% and 9.2%, respectively in lymphocytes incubated with the same volume of a water extract from non-heated oil (NHO) or distilled water (DW). In HepG2 or HUVEC cells, the cytotoxic properties of the HO were dose dependent, the cytotoxicity beginning at concentrations as low as 0.25 microM. In contrast, the same volume of NHO or DW was non-toxic for these cells. The results obtained show that a water extract obtained from heated oil is clastogenic and, in higher doses, cytotoxic.

In vitro inhibition of lipid peroxidation in fish by turmeric (Curcuma longa)

The beneficial effects of ∈-3 fatty acids on human health have been well documented. Fish and fish oils are the richest sources of ∈-3 fatty acids. However, due to their high degree of unsaturation, they are highly susceptible to lipid peroxidation. Regular consumption of peroxidised oils may represent a risk factor for the induction and development of atherosclerosis. In view of the above reports, it was considered necessary to study the effects of tumeric on fish lipid peroxidation during standard cooking practices and on time-dependent changes in the peroxidation of fish homogenate. The antioxidant effect of α-tocopherol was also studied to confirm the relevance of the study. The results suggest that turmeric may be considered as a safe, cheap and readily usable antioxidant for food preparations.