Study by 1H NMR spectroscopy of the evolution of extra virgin olive oil composition submitted to frying temperature in an industrial fryer for a prolonged period of time

Use of egg yolk phospholipids to improve the thermal-oxidative stability of fatty acids, capsaicinoids and carotenoids in chili oil

Phospholipids can act as antioxidants in food. In this study, egg yolk phospholipids (EPL) and sunflower oil were utilized in making chili oil, and proton nuclear magnetic resonance spectroscopy was employed to quantify the concentrations of fatty acyl groups, carotenoids, capsaicinoids in chili oil according to their specific signals in the spectra. The results showed that the changes in the concentrations of fatty acyl groups in the control samples were greater than those in the EPL-treated samples at the same frying temperature, while the contents of carotenoids and capsaicinoids were significantly lower than those of the EPL-treated samples when fried at 150 °C (p < 0.05). Two-way ANOVA indicated that frying temperature and EPL treatment, as well as their interaction had significant impacts on the thermal-oxidative stability of chili oil (p < 0.05). The results suggest that EPL may act as antioxidants during frying, and EPL can improve the thermal-oxidative stability of chili oil.

Study by means of 1H nuclear magnetic resonance of the oxidation process in high oleic sunflower oil and palm oil during deep-frying of fish cakes

This study aimed to compare the frying performance of palm oil (PO) and high oleic sunflower oil (HOSO) during frying aquatic products. The quality change and frying performance of HOSO and PO during frying of fish cakes were investigated. The oxidation and hydrolysis products of both oils were explored by the nuclear magnetic resonance technique. The results showed that the color deepening rate of PO was higher than that of HOSO. After 18 h of frying, the total polar compound content of PO and HOSO reached 25.67% and 27.50%, respectively. HOSO had lower degree of oxidation than PO after 24 h of continuous frying. The polyunsaturated fatty acid content in HOSO and PO significantly decreased. The oleic acid content in HOSO remained above 80% during the frying process. The major aldehydes in both oils were (E, E)-2,4-alkadienals and n-alkanals and glycerol diesters (DAGs) were abundant in PO. Furthermore, the addition of fish cakes had slight effect on the quality of the frying oil. Therefore, HOSO is an appropriate candidate for frying owing to its excellent frying stability and nutritional value.

Egg yolk phospholipids as an ideal precursor of fatty note odorants for chicken meat and fried foods: A review

Egg yolk phospholipids (PLs) have been demonstrated to generate large quantities of lipid-derived odorants, especially the fatty note odorants. Recently, egg yolk PLs have been successfully used in chicken meat and fried foods to improve aroma. This review comprehensively summarizes the properties of egg yolk PLs as precursors of fatty note odorants, including their classes, extraction, identification, oxidation, decomposition and odorant formation, applications, considerations and future prospects in the food industry. Most likely, phosphatidylcholine (PC) is the most abundant class in egg yolk PLs, and PC is more efficient than phosphatidylethanolamine in generating fatty note odorants; moreover, the predominant polyunsaturated fatty acid is linoleic acid, and its corresponding predominant hydroperoxide is 9-hydroperoxy-10,12-octadecadienoic acid during autoxidation, which is the precursor of 2,4-decadienals and 2,4-nonadienals, the key fatty note odorants. Therefore, egg yolk PLs could be an ideal precursor of fatty note odorants for chicken meat and fried foods.

Machine Learning-based Predictive Analysis of Total Polar Compounds (TPC) content in Frying Oils: A Comprehensive Electrochemical Study of 6 Types of Frying Oils with Various Frying Timepoints

Standard approaches to determining the total polar compounds (TPC) content in frying oils such as the chromatographic techniques are slow, bulky, and expensive. This paper presents the electrochemical analysis of 6 types of frying oils inclusive of 52 frying timepoints, without sample preparation. This is achieved via impedance spectroscopy to capture sample-specific electrical polarization states. To the best of our knowledge, this is a first-of-its-kind comprehensive study of various types of frying oils, with progressively increasing frying timepoints for each type. The principal component analysis distinguishes the frying timepoints well for all oil types. TPC prediction follows, involving supervised machine learning with sample-wise leave-one-out implementation. The R² values and mean absolute errors across the test samples measure 0.93-0.97 and 0.43-1.19 respectively. This work serves as a reference for electrochemical analysis of frying oils, with the potential for portable TPC predictors for rapid accurate screening of frying oils.

Possibility of using low-field nuclear magnetic resonance (LF-NMR) and differential scanning calorimetry (DSC) to monitor frying oil degradation

In this work, chemical degradation of oil was determined as a function of frying time during intermittent deep-fat frying (i.e. 185 °C for 5 h per day for 12 days) and was correlated with the thermal characteristics as measured by Differential Scanning Calorimetry (DSC) and proton mobility by Low-Field Nuclear Magnetic Resonance (LF-NMR). Linear increases of FFAs and PV were observed as a function of frying time. FFAs and PV were strongly correlated with the melting enthalpy. The melting enthalpy of oil decreased exponentially, and the melting temperature remained nearly same until 30 h of frying time followed by a sharp increase. The relaxation times of rigid, semi-rigid and mobile protons (i.e. T 2b , T 21 , and T 22 ) decreased with the increase of frying time. The decrease of T 21 , and T 22 were steeper as compared to the T2b. A strong correlation was observed between conventional chemical parameters (i.e. PV and FFAs), and T 21 and T 22. The populations of the three pools of protons as identified by Inverse Laplace Transformation and Gaussian distribution function showed the interchange of the protons with the chemical changes during frying. It is concluded that chemical free DSC and LF-NMR could be potential methods to monitor frying oil degradation.

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.

Individual and Joint Effect of Alpha-Tocopherol and Hydroxytyrosol Acetate on the Oxidation of Sunflower Oil Submitted to Oxidative Conditions: A Study by Proton Nuclear Magnetic Resonance

This study tackles the individual and joint effect of alpha-tocopherol and hydroxytyrosol acetate on the oxidation of sunflower oil submitted to accelerated storage conditions at intermediate temperature, in order to deepen the understanding of antioxidant–prooxidant behaviour. This was accomplished by ¹H Nuclear Magnetic Resonance. For this purpose, the evolution of the degradation of both the main components of the oil and the aforementioned added compounds was monitored by this technique throughout the storage time. Furthermore, the formation of a very large number of oxylipins and the evolution of their concentration up to a very advanced stage of oil oxidation, as well as the occurrence of lipolysis, were also simultaneously studied. The results obtained show very clearly and thoroughly that in the oxidation process of the oil enriched in binary mixtures, interactions occur between alpha-tocopherol and hydroxytyrosol acetate that notably reduce the antioxidant effect of the latter compound with the corresponding negative consequences that this entails. The methodology used here has proved to be very efficient to evaluate the antioxidant power of mixtures of compounds.

Utilization of Diaphragma juglandis extract as a natural antioxidant for improving the oxidative stability of soybean oil during deep frying

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Stabilization of oils during deep-frying by Diaphragma juglandis extract was studied.

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A total of 31 polyphenols were determined in Diaphragma juglandis extract.

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The extract is proven to inhibit the deterioration of triglycerides during frying.

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Extract-added frying oils exhibit a lesser increase in aldehydes and alcohols.

Lipid oxidation significantly shortens the life of frying oils, and this challenge can be addressed by using antioxidants. This work aimed to investigate the effect of Diaphragma juglandis extract (DJE) on the oxidative stability of soybean oil during deep frying. Tert-butylhydroquinone (TBHQ) and tea polyphenol (TP) were applied as positive controls. A total of 31 polyphenols were determined in DJE, and catechin, quercitrin, taxifolin, quercetin 3-β-d-glucoside, epicatechin, gallic acid, and 3,4-dihydroxybenzoic acid were the main components. The antioxidants effectively delayed the degradation of triglycerides and inhibited the increase in the contents of p-anisidine, oxidized triglyceride monomers, triglyceride dimers, and triglyceride oligomers, with DJE exhibiting better performance. Moreover, DJE showed better inhibitory effect on the formation of (E)-2-alkenals, (E,E)-2,4-alkadienals, 4-oxo-alkanals, primary alcohols, and secondary alcohols detected by ¹H nuclear magnetic resonance than TBHQ and TP. Therefore, DJE has great potential as an excellent antioxidant in large-scale industrial applications.

Influence of Hydroxytyrosol Acetate Enrichment of an Oil Rich in Omega-6 Groups on the Evolution of Its Oxidation and Oxylipin Formation When Subjected to Accelerated Storage. A Global Study by Proton Nuclear Magnetic Resonance

Sunflower oil samples, both unenriched and enriched with four different concentrations of hydroxytyrosol acetate, were subjected to accelerated storage at 70 °C until a very advanced oxidation stage and the process was monitored by ¹H NMR spectroscopy. The aim of the study is to know the effect that the presence of this antioxidant has on the oxidation process of sunflower oil under the aforementioned conditions, as well as on the formation and evolution of the concentration of a significant number of oxylipins. The oxidation process was studied globally by monitoring, during storage time, the degradation of both the linoleic acyl group of sunflower oil, which is the main component of sunflower oil, and the added hydroxytyrosol acetate. Simultaneously, the identification of up to twenty-six different types of oxylipins formed in the oxidation process and the monitoring of the evolution of their concentration over the storage time were carried out. In this way, essential information about the effect that hydroxytyrosol acetate provokes on the oxidation of this oil rich in omega-6 polyunsaturated acyl groups, has been obtained. It has also been shown that the enrichment of sunflower oil with this antioxidant under the conditions tested does not prevent the oxidation process but slows it down, affecting the entire oxidation process.

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.

Alpha-Tocopherol, a Powerful Molecule, Leads to the Formation of Oxylipins in Polyunsaturated Oils Differently to the Temperature Increase: A Detailed Study by Proton Nuclear Magnetic Resonance of Walnut Oil Oxidation

Lipid oxidation causes food degradation and the formation of toxic compounds. Therefore, the addition to foods of compounds able to avoid, delay or minimize this degradative process is a commonly used strategy. Nevertheless, neither the identity of most of the formed compounds in this complex process nor the way in which their formation is affected by the strategy used are well known. In this context, the effect the temperature increase and the enrichment level in alpha-tocopherol on the evolution of the walnut oil oxidation, as a model of an oil rich in polyunsaturated omega-6 acyl groups, submitted to storage conditions, are tackled by ¹H NMR. The study has allowed knowing the degradation kinetic of both the oil acyl groups and alpha-tocopherol, the identification of a very high number of oxylipins and the kinetic of their formation. The temperature increase accelerates the formation of all oxylipins, favouring the formation of hydroperoxy conjugated E,E-dienes and related derivatives versus that of the Z,E-isomers. The enrichment in alpha-tocopherol accelerates the formation of hydroperoxy conjugated Z,E-dienes and related derivatives, and delays in relation to the formation of the former that of the E,E-isomers and related derivatives, hindering, to a certain extent, the formation of the latter in line with the enrichment level.

Melting, Crystallization, and In Vitro Digestion Properties of Fats Containing Stearoyl-Rich Triacylglycerols

Fats containing the stearoyl-rich triacylglycerols (TAGs) of 1,2-distearoyl-3-oleoylglycerol (SSO) and 1,3-dioleoyl-2-stearoylglycerol (OSO) were synthesized via the lipase-catalyzed acidolysis of tristearin (SSS)-rich fat and oleic acids, followed by solvent fractionation. Their physicochemical properties and in vitro digestibilities were compared. The SSS-, SSO-, and OSO-rich fats comprised 81.6%, 52.9%, and 33.1% stearic acid, respectively, whereas oleic acid comprised 2.9%, 37.5%, and 56.2%, respectively. The SSS-, SSO-, and OSO-rich fats contained the TAGs of SaSaSa (100.00%), SaSaMo (86.98%), and MoSaMo (67.12%), respectively, and the major TAGs were SSS, SSO, and OSO, respectively. Melting and crystallization temperatures were higher and fat crystals were larger and densely packed in the descending order of SSS-, SSO and OSO-rich fats. Both in vitro multi-step digestion and pH-stat digestion were more rapid for OSO- than SSO-rich fat. Oleic acid was digested faster than stearic acid during the initial digestion, then the rate decreased, whereas that of stearic acid increased over prolonged digestion. Fats that were richer in stearoyl at the sn-1,3 position of TAG melted and crystallized at higher temperatures, had a densely packed microstructure of large fat crystals and were poorly digested. Stearic acid imparts the essential physical attributes of melting and crystallization in solid fats, and the low digestible stearoyl-rich fat would be a viable substitute for trans fatty acids in food lipid industry.

Regiospecific Positioning of Palmitic Acid in Triacylglycerol Structure of Enzymatically Modified Lipids Affects Physicochemical and In Vitro Digestion Properties

Tripalmitin-(PPP, 81.2%), 1,3-dipalmitoyl-2-oleoylglycerol-(POP, 64.4%), 1,2-dipalmitoyl-3-oleoylglycerol-(PPO, 86.5%), and 1,3-dioleoyl-2-palmitoylglycerol-(OPO, 50.2%)-rich lipids with different regiospecific positions of palmitic acid (P) were synthesized via acetone fractionation and lipase-catalyzed acidolysis, and their physicochemical and hydrolytic characteristics were compared. Triacylglycerols (TAGs) with higher content of P, wherein P was at the sn-1 (or 3) position, had higher melting points, crystallization temperatures, and packing densities of fat crystals compared to those with a lower content of P, and with P at the sn-2 position. The in vitro digestion degree calculated as released fatty acid (FA) (%) at 30, 60, and 120 min was in the following order: OPO-rich > PPO-rich > POP-rich lipids. At 120 min, in vitro digestion of the OPO-rich lipid released 92.6% of fatty acids, resulting in the highest digestibility, while 89.7% and 87.2% of fatty acids were released from the OPO-rich and PPO-rich lipids, respectively. Over the digestion period, the TAG and monoacylglycerol (MAG) contents decreased, while the diacylglycerol (DAG) content initially increased and then decreased, and the 1,2-DAG content exceeded the 1,3-DAG content. Therefore, the content and stereospecific position of P attached to a specific TAG affected the physicochemical and in vitro digestion characteristics of the lipids.

Characterization of Non-volatile Oxidation Products Formed from Triolein in a Model Study at Frying Temperature

Frying allows cooking food while promoting their organoleptic properties, imparting crunchiness and flavor. The drawback is the oxidation of triacylglycerides (TAGs), leading to the formation of primary oxidized TAGs. Although they have been associated with chronic and degenerative diseases, they are precursors of pleasant flavors in fried foods. Nevertheless, there is a lack of knowledge about the oxidation species present in foods and their involvement in positive/negative health effects. In this work, high-resolution (HR) C₃₀ reversed-phase (RP)-liquid chromatography (LC)-tandem HR mass spectrometry (MS/MS) was used to identify primary oxidation TAGs resulting from heating triolein (160 °C, 5 min). This allows simulating the initial heating process of frying oils usually used to prepare fried foods, such as chips, crisps, and snacks. Beyond hydroxy, dihydroxy, hydroperoxy, and hydroxy-hydroperoxy derivatives, already reported in phospholipids oxidized by Fenton reaction, new compounds were identified, such as dihydroxy-hydroperoxy-triolein derivatives and positional isomers (9/10- and 9/12-dihydroxy-triolein derivatives). These compounds should be considered when proposing flavor formation pathways and/or mitigating lipid-derived reactive oxygen species occurring during food frying.

Effects of ten vegetable oils on heterocyclic amine profiles in roasted beef patties using UPLC-MS/MS combined with principal component analysis

Soybean oil (SBO), rapeseed oil (RSO), peanut oil (PO), corn oil (CO), olive oil (OO), sunflower oil (SFO), rice germ oil (RGO), walnut oil (WO), torreya seed oil (TSO), and grapeseed oil (GSO) were used to investigate the formation of heterocyclic amines (HAs) in roasted beef patties. Seven HAs, including 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3,4-dimethyl-3H-imidazo[4,5-f]quinolone (MeIQ), 2-amino-3-methyl-3H-imidazo[4,5-f]quinoxaline (IQx), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 1-methyl-9H-pyrido[3,4-b]indole (harman), and 9H-pyrido[3,4-b]indole (norharman) were detected in control patties and patties with vegetable oils. GSO, SFO, and WO greatly reduced the content of PhIP and MeIQ. 1.25%TSO and 3.75% RGO showed higher inhibition effects on the more strongly mutagenic compounds (PhIP, MeIQ, IQx, 4,8-DiMeIQx, MeIQx). SBO, PO, and RSO promoted imidazoquin(ox)aline (MeIQ, MeIQx, 4,8-DiMeIQx, and IQx) and β-carboline (harman and norharman); 1.25% SBO had the most significant promoting effect on total HA. This could be useful for the reduction of HA by selecting oils during cooking.

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.

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

The minor components of vegetable oils are important for their oxidative stability. In order to know to what extent they can influence oil behaviour under oxidative conditions, two commercial soybean oils, one virgin and the other refined, both with very similar compositions in acyl groups but differing in their minor component profiles, were subjected to accelerated storage conditions. They were characterized by ¹H nuclear magnetic resonance (NMR) and direct immersion solid-phase microextraction coupled to gas chromatography/mass spectrometry (DI-SPME-GC/MS), while oil oxidation was monitored by ¹H-NMR. The lower levels of tocols and sterols in the virgin oil, together with its higher free fatty acid content when compared to the refined one, result in a lower oxidative stability. This is deduced from faster degradation of acyl groups and earlier generation of hydroperoxides, epoxides, and aldehydes in the virgin oil. These findings reveal that commercial virgin soybean oil quality is not necessarily higher than that of the refined type, and that a simple and rapid analysis of oil minor components by DI-SPME-GC/MS would enable one to establish quality levels within oils originating from the same plant species and similar unsaturation level regarding composition in potentially bioactive compounds and oxidative stability.

Fast, direct and in situ monitoring of lipid oxidation in an oil-in-water emulsion by near infrared spectroscopy

Lipid oxidation has implications on food, cosmetics and other fat containing products. Fatty acid autoxidation alters both the quality and safety of these products. Efficient and fast methods are needed to track lipid oxidation in complex systems. In this study, an oil-in-water emulsion (20% v/v of fish oil stabilized with high oleic sunflower lecithin) was subjected to iron-initiated oxidation. Conjugated dienes (CDs) were measured after fat extraction using a standardized method. Near infrared spectroscopy (NIRS) has been used to record chemical changes occurring during oxidation directly in the emulsion. Variations were noticed in different spectral regions. Partial least squares regression (PLSR) revealed correlations between conjugated diene values and NIRS spectra. High coefficients of determination (R2 = 0.967 and 0.996) were found for calibration and prediction respectively. The CD value was predicted from NIRS spectra with an error of 7.26 mmol eq. LH kg-1 oil (7.8% error). Limits of detection (LOD) and quantification (LOQ) of 4.65 and 15.5 mmol eq. LH kg-1 oil were estimated. NIRS is a rapid and simple method for measuring lipid oxidation (CD value) in an emulsion without prior fat extraction. NIRS can replace the reference methods that use hazardous solvents and consume time. Therefore, NIRS enables in-line monitoring for process and quality control.

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

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.

Study of the In Vitro Digestion of Olive Oil Enriched or Not with Antioxidant Phenolic Compounds. Relationships between Bioaccessibility of Main Components of Different Oils and Their Composition

The changes provoked by in vitro digestion in the lipids of olive oil enriched or not with different phenolic compounds were studied by proton nuclear magnetic resonance (¹H NMR) and solid phase microextraction followed by gas chromatography/mass spectrometry (SPME-GC/MS). These changes were compared with those provoked in the lipids of corn oil and of virgin flaxseed oil submitted to the same digestive conditions. Lipolysis and oxidation were the two reactions under consideration. The bioaccessibility of main and minor components of olive oil, of phenolic compounds added, and of compounds formed as consequence of the oxidation, if any, were matters of attention. Enrichment of olive oil with antioxidant phenolic compounds does not affect the extent of lipolysis, but reduces the oxidation degree to minimum values or avoids it almost entirely. The in vitro bioaccessibility of nutritional and bioactive compounds was greater in the olive oil digestate than in those of other oils, whereas that of compounds formed in oxidation was minimal, if any. Very close quantitative relationships were found between the composition of the oils in main components and their in vitro bioaccessibility. These relationships, some of which have predictive value, can help to design lipid diets for different nutritional purposes.

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

The effect of enriching virgin flaxseed oil with dodecyl gallate, hydroxytyrosol acetate or gamma-tocopherol on its in vitro digestion is studied by means of proton nuclear magnetic resonance and solid phase microextraction followed by gas chromatography/mass spectrometry. The extent and pattern of the lipolysis reached in each sample is analyzed, as is the bioaccessibility of the main oil components. None of the phenolic compounds provokes inhibition of the lipase activity and all of them reduce the lipid oxidation degree caused by the in vitro digestion and the bioaccessibility of oxidation compounds. The antioxidant efficiency of the three tested phenols is in line with the number of phenolic groups in its molecule, and is dose-dependent. The concentration of some minor oil components such as terpenes, sesquiterpenes, cycloartenol and 24-methylenecycloartenol is not modified by in vitro digestion. Contrarily, gamma-tocopherol shows very low in vitro bioaccessibility, probably due to its antioxidant behavior, although this increases with enrichment of the phenolic compounds. Oxidation is produced during in vitro digestion even in the presence of a high concentration of gamma-tocopherol, which remains bioaccessible after digestion in the enriched samples of this compound.

Effect of the Enrichment of Corn Oil with alpha- or gamma-Tocopherol on Its in Vitro Digestion Studied by 1H NMR and SPME-GC/MS; Formation of Hydroperoxy-, Hydroxy-, Keto-Dienes and Keto-E-epoxy-E-Monoenes in the more alpha-Tocopherol Enriched Samples

The aim of this study is the analysis of the in vitro digestion of corn oil, and of the effect of its enrichment with three levels of gamma- and alpha-tocopherol, by using, for the first time, 1H nuclear magnetic resonance (1H NMR) and a solid phase microextraction followed by gas chromatography/mass spectrometry (SPME-GC/MS). The attention is focused on the hydrolysis degree, the degradation of oil's main components, the occurrence of oxidation reactions and main compounds formed, as well as on the bioaccessibility of oil's main components, of compounds formed in the oxidation, and, of gamma- and alpha-tocopherol. The lipolysis levels reached are high and show a similar pattern in all cases. The oxidation of corn oil components during in vitro digestion is proven, as is the action of gamma-tocopherol as an antioxidant and alpha-tocopherol as a prooxidant. In the more alpha-tocopherol enriched samples, hydroperoxy-, hydroxy-, and keto-dienes, as well as keto-epoxy-monoenes and aldehydes, are generated. The bioaccessibility of the oil's main components is high. The compounds formed in the oxidation process during in vitro digestion can also be considered bioaccessible. The bioaccessibility of alpha-tocopherol is smaller than that of gamma-tocopherol. The concentration of this latter compound remains unchanged during the in vitro digestion of the more alpha-tocopherol enriched oil samples.

Solvent-based strategy improves the direct determination of key parameters in edible fats and oils by 1 H NMR

BACKGROUND

Edible fats and oils are very important in nutrition and as a main source of energy and are also essential nutrients. There are several methods for the analysis of edible fats and oils, but nowadays nuclear magnetic resonance (NMR) is emerging as a powerful tool (albeit complex and high-tech demanding) to identify, quantify, and differentiate many types of food, including fats and oils. In this sense, the challenges of this technique are the simplification of methodology and taking advantage of a 400 MHz NMR instrument.

RESULTS

Through an adequate mixture of solvents, we have developed a methodology to quantify essential parameters in edible fats and oils, including 1,2-diacylglycerol, 1,3-diacylglycerol, and 1-monoacylglycerol, by using a single experiment and without the need for matrix derivatization.

CONCLUSION

This methodology has been successfully applied to the analysis of olive, sunflower, corn, sesame, and peanut oils, as well as butter, walnut, salmon, and spicy pork sausage. Moreover, the evolution of thermal oxidation and lipolysis of virgin olive oil and sunflower has been analyzed. © 2020 Society of Chemical Industry.

Changes provoked by nixtamalization and tortilla making in the lipids of two corn varieties. A study by 1H NMR

The aim of this study is to analyze in depth, by means of proton nuclear magnetic resonance, ¹H NMR, the changes caused by nixtamalization and tortilla making in the lipid composition of two corn varieties. This technique permits the characterization of not only main but also minor lipid components of both corn and tortilla. Ferulates have been found for the first time among the minor components of these lipids. It has been proved that this processing affects the lipids of both corn varieties in a similar way. The total loss of fatty acids occurs as does partial loss of minor components. Furthermore, a slight oxidation is provoked during this processing as well as a small reduction in the unsaturation degree of the lipids. In spite of this a similar distribution of the different kinds of acyl groups has been found in corn and tortilla within each variety.

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

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 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.

Oxidation degree of soybean oil at induction time point under Rancimat test condition: Theoretical derivation and experimental observation

Indices including conductivity, short-chain carboxylic acids, total polar material, acid value, peroxide value and fatty acid composition in water or oil were monitored during Rancimat test of soybean oil from 90 °C to 120 °C. Formic, acetic, propionic and butyric acids in water were detected by ion chromatography. The results showed that all indices had two-stage oxidation rates of initiation (k_i) and propagation (k_p) at each temperature. Induction period (IP) computed from conductivity and other indices were well correlated (R² = 0.9980-0.9999). According to the Arrhenius model and empirical equation, k_i increased exponentially with temperature (T) while IP decreased exponentially with T. Oxidation degree of oil at induction time point IP*k_i was found to be independent of heating time and temperature. The transition between two models was theoretically derived and proved by H NMR. Evaluation of IP*k_i may provide a new route to correlate Rancimat data with shelf life of edible oil.

Monitoring of minor compounds in corn oil oxidation by direct immersion-solid phase microextraction-gas chromatography/mass spectrometry. New oil oxidation markers

The aim of this study is to shed light on the evolution of the minor compounds in the corn oil oxidation process, through the information provided by direct immersion-microextraction in solid phase followed by gas chromatography/mass spectrometry (DI-SPME-GC/MS). This methodology enables one, in a single run, to establish the identity and abundance both of original oil minor components, some with antioxidant capacity, and of other compounds coming from both main and minor oil components oxidation. For the first time, some of the compounds formed from oil minor components degradation are proposed as new markers of oil incipient oxidation. Although the study refers to corn oil, the methodology can be applied to any other edible oil and constitutes a new approach to characterizing the oxidation state of edible oils.

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.

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.

A thorough insight into the complex effect of gamma-tocopherol on the oxidation process of soybean oil by means of 1H Nuclear Magnetic Resonance. Comparison with alpha-tocopherol

The effect of γ-tocopherol in proportions between 0.02 and 2% by weight on the accelerated storage process of refined soybean oil is studied by ¹H NMR, and compared with that of α-tocopherol. Whereas the lowest γ-tocopherol enrichment level does not affect oil evolution, at higher concentrations both γ- and α-tocopherols initially accelerate acyl groups degradation and hydroperoxides generation, more as higher is the tocopherol concentration, this effect being less marked for γ-tocopherol. However, after this initial stage, the rates of acyl groups degradation and hydroperoxides formation decrease with tocopherol concentration. Furthermore, in the case of γ-tocopherol, the higher the enrichment degree, the later hydroperoxides decomposition occurs, so that, unlike α-tocopherol, γ-tocopherol delays the generation of most secondary oxidation products (aldehydes, (E,E)-keto-dienes, epoxy-keto-enes, (E)-epoxystearates and alcohols) with the exception of some epoxides. Similarly to α-tocopherol, γ-tocopherol modifies the oil oxidation pathway at the highest addition level, promoting the formation of compounds with (Z,E)-isomerism, although less noticeably than α-tocopherol.

Analysis of olive oil for authentication and shelf life determination

High-field proton (1H) nuclear magnetic resonance (NMR) spectroscopy was applied for screening the fatty acyl contents of 33 olive oil samples from five different geographical regions of Turkey to do geographical discrimination analysis. The 1H NMR data were subjected to principal component analysis (PCA) and analysis of variance (ANOVA) to discriminate the origin of olive oils. The combination of discriminative screening by 1H NMR and ANOVA did not require further analysis of olive oil such as gas chromatography (GC). ANOVA was employed for samples from three regions separately: Marmara Region (MR), Aegean Region (AR), and Mediterranean Region (MeR). The best discriminative parameter was the 1H NMR signal of linoleoyl acyl content. Applying both quantitative NMR and statistical analysis indicated that samples from different provinces within each geographical region (MR, AR, and MeR) could be discriminated. Comparing the linoleoyl and oleoyl acyl contents of Turkish olive oils with these of some Mediterranean olive oils showed the possibility of distinguishing the Turkish olive oils. 1H NMR spectra of three olive oil samples with the production years of January 2013, January 2014, and January 2015 were acquired in 2016 for discussing shelf life of olive oil by quantifying fatty acyls content, and determining minor constituents and possible by-products during storage. The effects of altitude and soil quality on fatty acyl contents of olive oil samples from a small olive growing village in Northeastern Turkey were also tested.

Characterization and migration of oil and solids in oily sludge during centrifugation

The migration behaviors of oil, water and solids in sludge during centrifugation were elaborated. Size distribution, surface topography and lypohydrophilic properties were studied in detail. The average size of solids was 61 μm in original sludge, 31 μm in upper layer and 235 μm in bottom layer. The result shows that solvent is essential to separate oil phase into molecular light and weight fractions during centrifugation. With solvent/oil ratio increases from 1:2, 1:1, 2:1 to 5:1, molecular weight in upper layer decreases from 1044, 1043, 1020 to 846 combined with that in bottom layer increases. A model was proposed to calculate the oil residue content in solid phases after sedimentation. The findings of this paper provide information for optimizing the oil recovery and clean treatment.