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1H-NMR Spectroscopy as a New Tool in the Assessment of the Oxidative State in Edible Oils
Abstract
Within the course of lipid peroxidation, hydroperoxides are formed as primary products. They can be used as analytical markers to assess the deterioration status of oils and fats. Here a new 1H-NMR assay to determine the hydroperoxide amount in edible oils is presented. We were able to show that the analytical performance of the method is similar to that of the commonly used peroxide value (PV) according to Wheeler. A total of 290 edible oil samples were analyzed using both methods. For some oil varieties considerable discrepancies were found between the results obtained. In the case of black seed and olive oil, two substances could be identified that cause positive (black seed oil) and negative (olive oils) deviations from the theoretical PV expected from the NMR values.
... Skiera et al. [130] utilized a similar methodology to that in [127] in order to investigate in detail the effect of solvents with significantly different dielectric constants and solvation ability (benzene-d 6 , CDCl 3 , acetone-d 6 and DMSO-d 6 ) and their binary mixtures, on the chemical shifts and linewidths of the hydroperoxide protons. CDCl 3 /DMSO-d 6 (5:1 v:v) appears to be an optimum binary mixture, which results in a significant deshielding in the range of 10.1-11.00 ...
... It was concluded that very sharp resonances of the hydroperoxide protons with ∆ν 1/2 < 3 Hz are required for the successful implementation of the 1 H-13 C HMBC experiment. This condition is easily met in the case of methyl-ester derivatives; however, with free fatty acids and samples of interest, for example, in food chemistry it may be necessary to use DMSOd 6 /CDCl 3 as solvents [130] to sufficiently reduce the line widths of the -OOH protons. ...
... These types of studies will be of importance not only in the field of food science but also in related scientific disciplines. The identification and specific resonance assignment of oxylipins, however, could be significantly facilitated, taking into consideration (i) the excellent resolution of the hydroperoxide protons obtained with the use of CDCl 3 /DMSO-d 6 binary mixtures [130,135], and (ii) the great potentialities of the use of band-selective 1D-NOESY, 1D-TOCSY, and 2D 1 H-13 C HMBC experiments [135,137,138] (see Sections 11.2, 11.3 and 11.5). ...
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.
... So far, a major impediment for unravelling the mechanistic role of epoxides and validating their use as early marker is the lack of simple and high-throughput quantitative methods. Nuclear Magnetic Resonance (NMR) has been shown in recent years as a convenient tool to assess lipid oxidation products quantitatively and rapidly Skiera, Steliopoulos, Kuballa, Holzgrabe, & Diehl, 2012). NMR has been used to quantify epoxides in chemically and thermally epoxidised fatty acid esters and oil samples, when most double bonds are converted into epoxides (Goicoechea & Guillen, 2010; 70 obtained via auto-oxidation under moderate shelf-life conditions, the epoxide structures are more diverse, and their concentrations are orders of magnitude lower. ...
... The spectral integration region to determine I was δH 4.4 to 4.0 ppm, with N corresponding to the four outer protons of the TG backbone. The TG backbone was not expected to undergo changes upon oxidation, hence its 1 H NMR signal was used as internal standard (Skiera et al., 2012). The integrals I are determined from the spectral integration regions listed in Table 1, all with N corresponding to 2. The proposed correction factor K was built on the theoretical constant k (Lewis et al., 2007), according to Eq 3.3. ...
... ThioBarbituric Acid Reactive Substances (TBARS), chromatographic methods Steenhorst-Slikkerveer, Louter, Janssen, & Bauer-Plank, 2000) and Nuclear Magnetic Resonance (NMR)Skiera, Steliopoulos, Kuballa, Holzgrabe, & Diehl, 2012). These approaches, however, focus on stable products and are not designed to capture the radical intermediates, which are critical components for mechanistical understanding. ...
... [25,26] A further NMR method was developed by Skiera et al.; here hydroperoxides ( = 10.5-11.5 ppm) were quantified directly. [20] The primary limitation of this NMR method is the low sensitivity. Because various triacylglycerides lead to different hydroperoxides, the signal-to-noise ratio (S/N) of each individual hydroperoxide signal is low, and thus, the uncertainty of low-oxidized oils with PV < 10 meq/kg can increase to ≥10% of S/N of 30). ...
... [28] Thus, the NMR method according to Skiera et al. was not applicable for either low-oxidized oils or phospholipid-containing samples, whereby phospholipid-containing samples also cannot be examined by iodometric titration. [11,20] To overcome this challenge, an alternative quantitative NMR method was developed to determine the peroxide amount in edible oils by using triphenylphosphine (TPP) as a derivatization agent. TPP reacts with peroxides to form triphenylphosphine oxide (TPPO; Figure 2). ...
... Here, 1 H and 31 P NMR analyses were investigated as potential analytical techniques. The performance of the TPP NMR method was compared with the NMR method presented by Skiera et al. [20] and the iodometric titration method. [11] ...
Hydroperoxides are formed as the primary product during lipid oxidation, being analyzed as the peroxide value to detect the degradation level of oils and fats. As an alternative to the classical titration method according to Wheeler, a ¹H‐{³¹P} decoupled NMR method is developed using triphenylphosphine (TPP) as a tagging agent. TPP reacts with peroxides to form TPP oxides. The quantification of the peroxide value is performed by comparing the amount of reacted TPP oxide and non‐reacted TPP. This approach eliminates the requirement for an additional internal standard. Low‐oxidized oils (peroxide value < 3 meq/kg) and high‐oxidized oils with peroxide values of 150 meq/kg are precisely quantified with an relative standard deviation (RSD) of 4.90% and 0.16%, respectively. A total number of 108 oil samples are examined using the newly‐developed ¹H‐{³¹P} decoupled NMR method, indicating the applicability for vegetable oils and krill oils.
Practical Applications: The developed NMR method is applicable for the determination of the peroxide value in vegetable, marine and krill oils presenting a powerful alternative for the Wheeler titration method.
... Quantitative 1 H NMR (qNMR) profiling has been introduced as a high-throughput method that does not suffer from these drawbacks. 1,8,9 NMR has been shown to identify 15,16 and quantify 17,18 primary and secondary lipid oxidation products in bulk oils by using a binary CDCl 3 /DMSO-d 6 solvent. These investigations, however, focused on bulk oils in advanced stages of oxidation and did not address the structural complexity of oil-in-water emulsions. ...
... Therefore, its 1 H NMR signal can be used as internal standard. 18 The integrals I ox are determined from the spectral integration regions listed in Table 1, all with N ox corresponding to 1. Peroxide Value (PV). PV values were determined according to the international standard procedure ISO 3960. ...
... For the analysis of lipid oxidation products in food emulsions we used a binary solvent mixture, composed of 5:1 CDCl 3 /DMSO-d 6 . 18 The binary solvent was used because DMSO forms hydrogen bonds with hydroperoxides, which in turn narrowed the width of hydroperoxide signals and moved them downfield, resulting in well dispersed peaks. However, when dissolving a full emulsion into this binary solvent, the present water partially dissolved as well. ...
Lipid oxidation is one of the most important reasons for the compromised shelf life of food emulsions. A major bottleneck in unravelling the underlying mechanisms is the lack of methods that provide a rapid, quantitative and comprehensive molecular view on lipid oxidation in these heterogeneous systems. In this study, the unbiased and quantitative nature of 1H NMR was exploited to assess lipid oxidation products in mayonnaise, a particularly oxidation-prone food emulsion. An efficient and robust procedure was implemented to produce samples where the 1H NMR signals of oxidation products could be observed in a well resolved and reproducible manner. 1H NMR signals of hydroperoxides were assigned in a fatty acid and isomer specific way. Band-selective 1H NMR pulse excitation allowed immediate quantification of both hydroperoxides and aldehydes with high throughput and high dynamic range at levels of 0.03 mmol/kg with high precision (RSDR = 5.9%). Explorative multivariate data modelling of the quantitative 1H NMR profiles revealed that shelf life temperature has a significant impact on lipid oxidation mechanisms.
... Each sample was analyzed in triplicate. PL-BA, PL-E, and CLO sampled at 0, 17, and 70 h during the Schaal oven test were screened for composition by 1 H NMR. Approximately, 100 mg of the sample were dissolved in 350 mL of a mixture of deuterated chloroform and dimethyl-sulfoxide (DMSO) (5:1, v/v) (as described in [32] for optimal resolution of hydroperoxide signals), and transferred to 3 mm NMR-tubes. NMR spectra were recorded on a Bruker Avance 600 MHz spectrometer (Bruker Biospin GmbH, Rheinstetten, Germany) at ambient temperature (25°C) with cryo-probe operating at a 1 H frequency of 600.23 MHz. ...
... 1 H NMR is a valuable technique for following changes in lipids due to lipid oxidation as shown in studies with both vegetable oils [32,46] and marine lipids [47,48]. ...
... ppm) increased, and several new peaks assigned to aldehydes (9.4-10.0 ppm) appeared [32]. In addition, a singlet at 8.22 ppm, assigned to formic acid, appeared and increased during the oxidation. ...
The objective of this study was to evaluate oxidative status and stability measurements of cod roe phospholipid (PL) extracts obtained by different extraction methods, and of two refined fish oils. The oxidative status varied depending on the method and on the extraction methods for the PL extracts. Peroxide value (PV) and anisidine value (AV) were not measurable in PL extracted by ethanol due to dissolution issues and precipitation occurring in the reaction mixture, the latter were attributed to co-extracted compounds. The thiobarbituric acid reactive substances (TBARS) values were significantly lower for determinations in the presence of an antioxidant in the reaction mixture for both fish oils and PL indicating that marine lipids may become oxidised in the course of the analysis. The accelerated oxidation revealed major differences in the pattern of oxidation in bulk fish oil and bulk PL. While for fish oils the level of omega-3 fatty acids decreased and the level of both peroxides and aldehydes increased, PL showed minor loss of omega-3 fatty acids, minimal presence of the oxidation markers accompanied by disappearance of phosphatidylethanolamine group. This study shows that the applicability of classical oxidation status methods on marine phospholipids is limited. Variations in the methods, such as the choice of lipid solvent/reaction medium, may also lead to different results. ¹H high resolution magnetic resonance spectroscopy NMR proved to be a valuable tool to study the different oxidation patterns of fish oils and PLs.
... So far, a major impediment for unravelling the mechanistic role of epoxides and validating their use as early marker is the lack of simple and highthroughput quantitative methods. In recent years, Nuclear Magnetic Resonance (NMR) spectroscopy has been shown to be a convenient tool to assess lipid oxidation products quantitatively and rapidly (Guillén & Ruiz, 2004;Guillen & Goicoechea, 2009;Skiera, Steliopoulos, Kuballa, Holzgrabe, & Diehl, 2012;Merkx, Hong, Ermacora, & van Duynhoven, 2018). It has been used to quantify epoxides in chemically oxidized and thermally autoxidized fatty acid esters and oil samples, when most double bonds are converted into epoxides (Goicoechea & Guillen, 2010;Xia et al., 2015;Xia, Budge, & Lumsden, 2016;Xia & Budge, 2017). ...
... The spectral integration region to determine I TG was δ H 4.4 to 4.0 ppm, with N TG corresponding to the four outer protons of the TG backbone. The TG backbone was not expected to undergo changes upon oxidation, hence its methylene 1 H NMR signal was used as internal standard (Skiera et al., 2012). The integrals I epox are determined from the spectral integration regions listed in Table S1, all with N epox corresponding to 2. The proposed correction factor K was built on the theoretical constant k (Lewis et al., 2007) according to Eq (3). ...
Lipid oxidation is detrimental for the quality of oil-based foods. Historically, lipid oxidation research focussed on hydroperoxides and aldehydes, but a third class, the epoxides, have been proposed to resolve observed mechanistic anomalies. Here, we developed a 2D ¹H-¹³C HSQC NMR spectroscopic method to quantify epoxides in food in a reproducible (relative standard deviation ≤ 11.6 %) and sensitive (LoQ 0.62 mmol/kg oil) manner. Lipid hydroperoxides, aldehydes, and epoxides generated in rapeseed oil and mayonnaise were quantified over time by NMR. Epoxides accounted at most for 10-40 % of the products. They were formed after hydroperoxide accumulation, most likely primarily via alkoxyl radical intermediates, which limits their potential as an early oxidation marker. As 99 % and ∼60 % of the epoxide signal intensities were assigned in a fatty acid and sub-structure specific manner, respectively, our quantitative HSQC method will enable unravelling and quantitative modelling of lipid oxidation mechanisms.
... Prior to the NMR experiments, the samples were dissolved in either pure solvent (CD 3 OD, CDCl 3 ) or solvent mixtures (CDCl 3 /CD 3 OD (3:2, 2:1, v:v) and CDCl 3 /DMSO-d 6 (5:1, v:v)). These solvents and solvent mixtures were previously proposed in the literature for NMR measurement of hemp extracts or edible oils [9,19,20,[22][23][24][25]. ...
... No OH groups were observed with the solvent CD 3 OD. This is in line with the fast proton-deuterium exchange of polar solvents [25,30] and constitutes an advantage for qNMR: These signals are often very broad in NMR spectra and in addition to the pH, the chemical shift also depends strongly on temperature [29] impeding reliable quantification. ...
Toxicologically relevant levels of the psychoactive ∆9-tetrahydocannabinol (∆9-THC) as well as high levels of non-psychoactive cannabinoids potentially occur in CBD (cannabidiol) oils. For consumer protection in the fast-growing CBD oil market, facile and rapid quantitative methods to determine the cannabinoid content are crucial. However, the current standard method, i.e., liquid chromatography combined with tandem mass spectrometry (HPLC-MS/MS), requires a time-consuming multistep sample preparation. In this study, a quantitative nuclear magnetic resonance spectroscopy (qNMR) method for screening cannabinoids in CBD oils was developed. Contrary to the HPLC-MS/MS method, this qNMR features a simple sample preparation, i.e., only diluting the CBD oil in deuterochloroform. Pulse length-based concentration determination (PULCON) enables a direct quantification using an external standard. The signal intensities of the cannabinoids were enhanced during the NMR spectra acquisition by means of multiple suppression of the triglycerides which are a major component of the CBD oil matrix. The validation confirmed linearity for CBD, cannabinol (CBN), ∆9-THC and ∆8-THC in hemp seed oil with sufficient recoveries and precision for screening. Comparing the qNMR results to HPLC-MS/MS data for 46 commercial CBD oils verified the qNMR accuracy for ∆9-THC and CBD, but with higher limits of detection. The developed qNMR method paves the way for increasing the sample throughput as a complementary screening before HPLC-MS/MS.
... Prior to the NMR experiments, the samples were dissolved in either pure solvent (CD3OD, CDCl3) or solvent mixtures (CDCl3/CD3OD (3:2, 2:1, v:v) and CDCl3/DMSO-d6 (5:1, v:v)). These solvents and solvent mixtures were previously proposed in the literature for NMR measurement of hemp extracts or edible oils [9,19,20,[22][23][24][25]. To assign the cannabinoid signals in the 1 H NMR spectrum of CBD oils, reference spectra of different cannabinoids were recorded in CDCl3 and their compoundspecific coupling constants, multiplicities, and chemical shift were recorded and verified with literature data. ...
... Moreover, the CBD spectra of pure CBD in CD3OD showed better resolution of the signals between 0 -3 ppm as in CDCl3 and the CBD signal of the aromatic protons at about 6.2 ppm turns out to be much narrower than in CDCl3 (see Figure S1). Another fundamental advantage of the polar solvent results from the fast proton-deuterium exchange, which means that no OH groups were observed in the spectrum [25,30]. These signals are often very broad in NMR spectra and in addition to the pH, the chemical shift also depends strongly on temperature [29]. ...
Toxicologically relevant levels of the psychoactive ∆9-tetrahydocannabinol (∆9-THC) as well as high levels of non-psychoactive cannabinoids potentially occur in CBD (cannabidiol) oils. For consumer protection in the fast-growing CBD oil market, facile and rapid quantitative methods to determine the cannabinoid content are crucial. However, the current standard method, i.e., liquid chromatography combined with tandem mass spectrometry (HPLC-MS/MS), requires a time-consuming multistep sample preparation. In this study, a quantitative nuclear magnetic resonance spectroscopy (qNMR) method for screening cannabinoids in CBD oils was developed. Contrary to the HPLC-MS/MS method, this qNMR features a facile sample preparation, i.e., only diluting the CBD oil in deuterochloroform. Pulse length-based concentration determination (PULCON) enables a direct quantification using an external standard. The signal intensities of the cannabinoids were enhanced during the NMR spectra acquisition by means of multiple suppression of the triglycerides which are a major component of the CBD oil matrix. The validation confirmed linearity for CBD, cannabinol (CBN), ∆9-THC and ∆8-THC in hemp seed oil with sufficient recoveries and precision for screening. Comparing the qNMR results to HPLC-MS/MS data for 46 commercial CBD oils verified the qNMR accuracy for ∆9-THC and CBD but with higher limits of detection. The developed qNMR method paves the way for increasing the sample throughput as a complementary screening before HPLC-MS/MS.
... In crude soybean oil, the main substrates for lipid oxidation are triacylglycerols (TAGs) and free fatty acids (FFAs), which make up 95-97% and 0.3-0.7% of oil, respectively 10,11 . Both TAGs and FFAs have been shown to oxidize during thermal treatment of oil 8,[12][13][14] . As shown in Fig. 1, there are two plausible pathways through which these substrates produce oxylipins in heated oil-(1) TAGs can undergo non-enzymatic hydrolysis to produce FFAs, which can oxidize to form free oxylipins (Pathway 1 in blue), or (2) fatty acids within a TAG molecule (i.e. ...
... Hence, more % FFA in a sample reflects more TAG hydrolysis into FFAs, and greater potential for the released FFAs to form primary oxidation products (i.e., oxylipins) and secondary volatiles. However, in oil, fatty acid hydroperoxides (a type of oxylipin) were detected in both TAGs and FFAs 8,[12][13][14] , suggesting that oxidation can occur directly on TAGs, or on FFAs following their release from TAGs. The preferential substrate for lipid oxidation remains unknown. ...
In oil, free fatty acids (FFAs) are thought to be the preferred substrate for lipid oxidation although triacylglycerols (TAGs) are the predominant lipid class. We determined the preferential oxidation substrate (TAGs versus FFAs) in soybean oil heated at 100 °C for 24 h, after validating a method for quantifying esterified and free lipid oxidation products (i.e., oxylipins) with mass-spectrometry. Reaction velocities and turnover (velocity per unit substrate) of FFA, and free and TAG-bound (esterified) oxylipins were determined. FFA hydrolysis rate and turnover were orders of magnitude greater (16-4217 fold) than that of esterified and free oxylipin formation. The velocity and turnover of TAG-bound oxylipins was significantly greater than free oxylipins by 282- and 3-fold, respectively. The results suggest that during heating, TAGs are preferentially oxidized over FFAs, despite the rapid hydrolysis and availability of individual FFAs as substrates for oxidation. TAG-bound oxylipins may serve as better markers of lipid oxidation.
... Skiera et al. [164] suggested a 1 H-NMR method for the quantification of hydroperoxides in edible oils. Proton transfer line width broadening of the hydroperoxide (OOH) signal was significantly eliminated using a mixture of CDCl 3 and DMSO-d 6 (5:1 v:v) and, thus, accurate integration could be obtained. ...
... Deuterated chloroform has been widely used in 1 H-and 13 C NMR since it is an excellent solvent for most lipids. For specific applications, mixtures of CDCl 3 and DMSO-d 6 have also been utilized [132,164]. DMSO-d 6 induces significant chemical shift changes with respect to those in CDCl 3 which should be taken into consideration when comparing literature data. The chemical shift of the residual 1 H-NMR signal of CDCl 3 and the 13 C signal of CDCl 3 have been commonly utilized for referencing. ...
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 including¹H¹³C- and³¹P-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 critical¹H-¹³C- and³¹P-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. 2017 by the authors.
... Rezzi et al. [19] and Camin et al. [20] have further demonstrated the feasibility of using 1 H-NMR to differentiate olive oil based on geographic origins with multivariate analysis. 1 H-NMR can also be as a novel technique to determine the oxidation level, identify the oxidation products and clarify the oxidation mechanism [21][22][23]. ...
Walnut oil is endowed with a variety of physiological functions due to abundant natural compounds, and the effect of unsaturated fatty acids is crucial. In order to accurately and conveniently detect the fatty acids components and content in walnut oil, a quantitative method was developed to detect fatty acids content based on the ¹H-NMR and ¹³C-NMR techniques. In addition, HPLC combined with MS was used to conduct qualitative analysis. HPLC method with an evaporative light-scattering detector was for the quantitative analysis and the fatty acids content was compared with the content from NMR. The result showed that there was no significant difference between ¹H-NMR, ¹³C-NMR and HPLC (P > 0.05) and indicated that the NMR has the potential to be applied as a routine method for the analysis of fatty acids content in walnut oil.
... The solvent was removed using a rotary evaporator (BUCHI Rotavapoor R-200, Brinkmann Instruments, Inc., Westbury, NY, USA) and the oil was transferred to a 5 mm diameter NMR tube [33]. The samples were analyzed in an NMR spectrometer (Ultrashield 500 MHz/54 mm, Bruker AG, Fallanden, Switzerland) for 1 h to obtain a signal for hydroperoxide, the primary product of lipid oxidation [34]. ...
Iron (Fe) deficiency is one of the most common nutritional disorders, and is mainly due to insufficient intake of bioavailable Fe. Chickpea (Cicer arietinum L.) was examined as a potential vehicle for Fe fortification. Fortificants (FeSO4·7H2O (ferrous sulfate hepta-hydrate), FeSO4·H2O (ferrous sulfate mono-hydrate) and NaFeEDTA (ethylenediaminetetraacetic acid iron (iii) sodium salt)) were applied by a spraying and drying method. At 2000 µg g−1 iron fortificant, the fortified split desi seeds (dal), desi flour and kabuli flour supplied 18–19 mg, 16–20 mg and 11–19 mg Fe per 100 g, respectively. The overall consumer acceptability using a nine-point hedonic scale for sensory evaluation demonstrated that NaFeEDTA-fortified cooked chickpea (soup and chapatti) scored the highest among the three fortificants. Lightness (L*), redness (a*) and yellowness (b*) of Fe-fortified products changed over time. However, no organoleptic changes occurred. Fe bioavailability was increased by 5.8–10.5, 15.3–25.0 and 4.8–9.0 ng ferritin mg−1 protein for cooked split desi seeds (soup), desi chapatti and kabuli chapatti, respectively, when prepared using Fe-fortified chickpea. Desi chapatti showed significantly higher Fe bioavailability than the other two. The increase in Fe concentration and bioavailability in fortified chickpea products demonstrated that these products could provide a significant proportion of the recommended daily Fe requirement.
... Skiera et al. [20] suggested an 1 H NMR method for the quantification of hydroperoxides in edible oils. Proton transfer linewidth broadening of the hydroperoxide (OOH) signal was significantly eliminated using a mixture of CDCl 3 and DMSO-d 6 (5:1 v:v), and, thus, accurate integration could be obtained. ...
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 1H‐13C HMBC NMR experiment for the identification and quantification of complex and minor (3.9 to 0.85 ‐per‐cent) 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.
... When a mixture of DMSO and CDCl 3 (preferably in the ratio 1:5) is used, the OOH protons of hydroperoxides appear around 11 ppm, and the signals have much smaller linewidths than in chloroform alone. Skiera et al. [17] used this mixture of solvents to demonstrate that the amount of peroxide obtained from NMR correlates very well with the classical "peroxide value, PV." Interestingly, in some cases significant deviations were observed, which could be traced back to the presence of hydroxytyrosol in olive oil, causing a decrease of the classical PV, and to the presence of thymoquinone in black seed oil, causing an increase of the classical PV. The results strongly suggest that the NMR method is a more accurate method to detect deterioration of oils. ...
This chapter reviews the use of NMR for compositional and quantitative analysis of oils and lipids in food. The literature of the past decade on the following topics is reviewed: High-resolution ¹³C NMR is a powerful method to determine the positional distribution of different classes of fatty acids on the glycerol backbone due to chemical shift differences observed on the carbonyl signal. Oxidation products such as aldehydes, hydroperoxides, and epoxides can be observed and quantified directly in the ¹H NMR spectrum of lipids. Results agree very well with classical methods such as determination of anisidine value and peroxide value. The advantage of NMR lies in the additional information obtained and the ease of sample preparation and the speed of the analysis in general. Minor components of oils and lipids such as sterols, polyphenols, and glycerol can be quantified either directly or after derivatization. In addition, conjugated fatty acids and galactolipids are observed. By means of ³¹P NMR, it is possible to identify and quantify all known phospholipids using various extraction or preconcentration methods. Also, the concentration of diglycerides and monoglycerides in the lipid matrix can be determined in a straightforward way without timeconsuming sample pretreatment. High-resolution ¹H NMR is also a very useful technique to obtain information on the fatty acid composition of oils, albeit more restricted to classes of fatty acids: saturated, monounsaturated, and polyunsaturated. Such information can also be obtained by means of low-field NMR when combined with chemometric methods. Time-domain NMR, finally, is a fast and cost-effective method to assess total lipid content and water content and to obtain information on the physical state of these components. © Springer International Publishing AG, part of Springer Nature 2018.
... However, some studies have already demonstrated the potential of the 1H Nuclear Magnetic Resonance (1H NMR) spectroscopy to explain physical characteristics of plant oils or their compositions based on large database representative of variability between botanical origins (Skiera, Steliopoulos, Kuballa, Holzgrabe, & Diehl, 2012a, 2012b. The NMR spectroscopy was used as an untargeted tool for the surveillance of dairy products which has allowed the investigation of particular fraud by means of the application of chemometric tools (Monakhova, Godelmann, Andlauer, Kuballa, & Lachenmeier, 2013). ...
Further to recent food scandals, consumers have become increasingly concerned about the quality and integrity of the processed products they buy and eat. Edible oils contaminations or deliberate adulterations are recurring issues. Until now the lipidic composition of food has not been extensively studied by Nuclear Magnetic Resonance (NMR) spectroscopy despite the fact that this analytical method can cover a wide range of matrices. The application of a refocused adiabatic ¹³C INEPT (Insensitive Nuclei Enhanced by Polarization Transfer) sequence has already proved the performance of NMR spectroscopy to discriminate the origins of olive oils. This sequence has been demonstrated to be faster than a classical ¹³C NMR sequence. In this work, the implementation of that ¹³C NMR sequence in a routine laboratory has allowed the analysis of 23 common origins of edible oils, as well as butters, margarines and animal fats. We have proven that butter origin could clearly be distinguished from plant oil origins considered in this work. With the example of the verification of palm oil presence in food products, we have demonstrated the applicability of the method to characterize fats origin in transformed products. This study has shown by means of chemometric tools the potential of ¹³C NMR spectroscopy to check the authenticity of various commercial finished products, using an untargeted approach applied to a spectral database of 294 spectra of raw animal and plant fats and oils. Thanks to spiking tests, the limit of detection of one origin of plant oil in another has been estimated as being around 5% and the limit of detection of animal oil in plant oils has been estimated as being around 2%. The same approach can be applied as a global method to verify the authenticity and integrity of fats and oils.
... When a mixture of DMSO and CDCl 3 (preferably in the ratio 1:5) is used, the OOH protons of hydroperoxides appear around 11 ppm, and the signals have much smaller linewidths than in chloroform alone. Skiera et al. [17] used this mixture of solvents to demonstrate that the amount of peroxide obtained from NMR correlates very well with the classical "peroxide value, PV." Interestingly, in some cases significant deviations were observed, which could be traced back to the presence of hydroxytyrosol in olive oil, causing a decrease of the classical PV, and to the presence of thymoquinone in black seed oil, causing an increase of the classical PV. The results strongly suggest that the NMR method is a more accurate method to detect deterioration of oils. ...
This chapter reviews the use of NMR for compositional and quantitative analysis of oils and lipids in food. The literature of the past decade on the following topics is reviewed: High-resolution 13C NMR is a powerful method to determine the positional distribution of different classes of fatty acids on the glycerol backbone due to chemical shift differences observed on the carbonyl signal. Oxidation products such as aldehydes, hydroperoxides, and epoxides can be observed and quantified directly in the 1H NMR spectrum of lipids. Results agree very well with classical methods such as determination of anisidine value and peroxide value. The advantage of NMR lies in the additional information obtained and the ease of sample preparation and the speed of the analysis in general. Minor components of oils and lipids such as sterols, polyphenols, and glycerol can be quantified either directly or after derivatization. In addition, conjugated fatty acids and galactolipids are observed. By means of 31P NMR, it is possible to identify and quantify all known phospholipids using various extraction or preconcentration methods. Also, the concentration of diglycerides and monoglycerides in the lipid matrix can be determined in a straightforward way without time-consuming sample pretreatment. High-resolution 1H NMR is also a very useful technique to obtain information on the fatty acid composition of oils, albeit more restricted to classes of fatty acids: saturated, monounsaturated, and polyunsaturated. Such information can also be obtained by means of low-field NMR when combined with chemometric methods. Time-domain NMR, finally, is a fast and cost-effective method to assess total lipid content and water content and to obtain information on the physical state of these components.
... The results obtained by the NMR method were in agreement with other traditional methods, peroxide value and TBARS. Skiera et al. (2012a) improved the methodology of the 1 H NMR spectroscopy so that the hydroperoxide (OOH) signal could be used as the marker of oil oxidation. The signal of the hydroperoxide (OOH) appears as a very broad peak when the most common NMR solvent, CDCl 3 , is used, and it is difficult to accurately integrate the peak. ...
The 31P NMR spectroscopy is not as frequently used as other NMR techniques. However, it can be very useful in case where strong signal overlap and dynamic range problems in 1H NMR spectra and/or long relaxation time of 31C NMR become a problem. It is known to be a better analytical method than time-consuming HPLC and TLC techniques in analyses of phospholipids in oil. The 31P NMR spectroscopy can also be used to determine the fatty acid distribution and to assess the oxidation of vegetable oils. The major drawback of 31P NMR is that the experimental procedure involves an additional step, the derivatization of functional groups in the oil sample with a phosphorus reagent. One of the major uses of this technique is to distinguish structurally similar compounds such as mono-, di-, and triacylglycerols.
... The results obtained by the NMR method were in agreement with other traditional methods, peroxide value and TBARS. Skiera et al. (2012a) improved the methodology of the 1 H NMR spectroscopy so that the hydroperoxide (OOH) signal could be used as the marker of oil oxidation. The signal of the hydroperoxide (OOH) appears as a very broad peak when the most common NMR solvent, CDCl 3 , is used, and it is difficult to accurately integrate the peak. ...
The NMR method has drawn great interest as a new method to assess the level of lipid oxidation since most of conventional analytical methods have some problems. The 1H NMR method monitoring the disappearance of starting materials was found to be very reliable for the assessment of lipid oxidation. In this chapter, the development of 1H NMR methods for the assessment of lipid oxidation during storage and frying will be discussed. Starting from the first method reported by Saito in 1987, a variety of 1H NMR methods developed by many research groups are introduced in this chapter. Early studies focused more on lipid oxidation at relatively lower temperatures such as storage temperatures or slightly higher temperatures for the acceleration of oxidation (25–70 °C) since the more oxidation products could be detected at a lower temperature. Later, it was found that there were significant differences between oxidation products and oxidation mechanisms with different oxidation temperatures. There are four different types of methods developed for the assessment of oxidation during frying: 1) Methods monitoring the changes of major NMR signals, 2) methods using the NMR proton relaxation time, 3) methods measuring acyl groups, and 4) methods measuring aldehydes and other oxidation product.
... The results obtained by the NMR method were in agreement with other traditional methods, peroxide value and TBARS. Skiera et al. (2012a) improved the methodology of the 1 H NMR spectroscopy so that the hydroperoxide (OOH) signal could be used as the marker of oil oxidation. The signal of the hydroperoxide (OOH) appears as a very broad peak when the most common NMR solvent, CDCl 3 , is used, and it is difficult to accurately integrate the peak. ...
There are a variety of analytical methods developed for the determination of lipid oxidation. However, many of them are old methods that depend on chemical reactions with a reagent, require long time and extensive labor, cannot be automated, measure only one kind of oxidation product, determine the concentration of an oxidation product that reaches a peak in a short time, and/or have inconsistencies due to multiple variations in the procedure. Modern analytical instruments, which can handle many samples at a time by automation, concomitantly detect many oxidation products, and be used for a long period of oxidation process, should be utilized to overcome the problems of current standard analytical methods. The NMR methods meet all these needs and should be more widely used for the analysis of lipids. More convenient, user-friendly NMR instruments such as small benchtop NMR instruments and software programs such as an automated analysis program for the fatty acid composition of vegetable oils have been developed.
... The results obtained by the NMR method were in agreement with other traditional methods, peroxide value and TBARS. Skiera et al. (2012a) improved the methodology of the 1 H NMR spectroscopy so that the hydroperoxide (OOH) signal could be used as the marker of oil oxidation. The signal of the hydroperoxide (OOH) appears as a very broad peak when the most common NMR solvent, CDCl 3 , is used, and it is difficult to accurately integrate the peak. ...
One of the most significant contributions of the 1H NMR technique is that it made major advances in elucidation of molecular structures of oxidation products. Since oxidation mechanisms and consequent oxidation products are different at different temperatures, this chapter is divided into two parts: 1) 1H NMR to indentify oxidation products during storage of oil and 2) 1H NMR to indentify oxidation products at frying temperatures. The study on oxidation products using 1H NMR was conducted as early as 1966 when Zimmerman utilized a very early model of the NMR instrument (60 MHz) to verify the isomerization of unsaturated hydroperoxide to a ketohydroxy compound. Since then, many oxidation products including hydroperoxides, aldehydes, ketones, alcohols, and epoxides were identified by the NMR method. One major difference between the oxidation products formed at relatively lower temperatures and at frying temperatures is that intermediate oxidation products such as hydroperoxides are not observed at frying temperatures because these intermediate oxidation products easily react with other compounds or decompose to produce secondary oxidation products. These intermediate products can be detected only when the oil was heated for a relatively short time at a frying temperature.
... The results obtained by the NMR method were in agreement with other traditional methods, peroxide value and TBARS. Skiera et al. (2012a) improved the methodology of the 1 H NMR spectroscopy so that the hydroperoxide (OOH) signal could be used as the marker of oil oxidation. The signal of the hydroperoxide (OOH) appears as a very broad peak when the most common NMR solvent, CDCl 3 , is used, and it is difficult to accurately integrate the peak. ...
Nuclear magnetic resonance (NMR) spectroscopy is one of the most powerful analytical tools to identify organic and bio-organic substances and to elucidate their chemical structures. Therefore, it has widely been used to analyze a variety of foods. Moisture content, solid fat content, fatty acid composition in lipid, free fatty acids, authenticity of edible oils, and the metabolic profile of sweet pepper can be analyzed by the NMR spectroscopy.
... Moreover, NMR does not produce changes in the nature of the sample and allows monitoring the changes and the concentration of the new molecules or functional groups formed during the Electronic supplementary material The online version of this article (doi:10.1007/s12161-016-0778-x) contains supplementary material, which is available to authorized users. thermooxidative process (Guillén and Uriarte 2012;Skiera et al. 2012;Jia et al. 2016). In this regard, important information can be obtained about adulteration, freshness, or degree of oxidation from the 1 H-NMR spectra (Dais and Hatzakis 2013;Castejón et al. 2014). ...
The culinary oils, sunflower and olive, and the oil from the cultivated cardoon (Cynara cardunculus L.) were submitted to deep-fat frying during 36 h. The heterospectroscopy analysis by nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) allowed to control oil quality through the monitor of (1) the percentage of fatty acid types (increase of saturated and decrease of polyunsaturated fatty acids), (2) the new compounds formed (aldehydes and peroxides), and (3) the oil oxidative stability during the deep-fat frying. The aldehyde content was much higher in sunflower and cynara oils than in olive; however, the epoxides increased more in this oil. Oxidative stability measured by EPR was correlated (p < 0.05) with the aldehyde formation measured by NMR. The multivariate analysis of the NMR data allowed classifying the oils depending on (a) the oxidation degree (PC1) and (b) the fatty acid composition (PC2). Moreover, the favorable behavior of cynara oil suggests the potential use as frying edible oil.
... However, 20 mg/L is just a recommendation from A.I.J.N. for fruit juice and not for soft drinks b All carbohydrates are higher than demanded concentration due to the wide concentration range from 1 to 50 mg/ L for glucose and fructose and 1-100 g/L for sucrose and because of the high content of these substances already present in matrix c The values for nicotinamide appear to be high; however, in fact, the demanded concentration is a recommended daily dose (mg) and not a maximum concentration Citric acid 100 200 300 400 500 mg/L 6 S u c r o s e a 45 g/L a For sucrose, a spiking series in each matrix was prepared five times; the determination was performed using an external calibration curve in water (linear concentration range 0.9-100 g/L with r = 0.9995). The linear equation was integrated in an automated analysis to determine concentrations 1964; Skiera et al. 2012). For example, the functional relationship between the enzymatic fructose values (y) and the NMRdetermined values (x) was found to be given by y ¼ 1:04x-1:79 ...
Nuclear magnetic resonance (NMR) spectroscopy is evaluated as an efficient analytical technique for simultaneous identification and quantitation of multiple compounds in alcohol-free beverages. The method was validated for three different types of soft drinks, including a beverage with high sugar content, a diet product and an energy drink. The sample preparation required only 600 μL of degassed soft drink, 70 μL of 0.1 % TSP-d4 in D2O (for referencing and locking) and 100 μL of phosphate buffer (pH = 2.89). The simultaneous quantitative analysis of eleven compounds, such as sugars, flavourings, sweeteners, organic acids, alcohol (ethanol), vitamins and amino acids, was achieved using an automated procedure based on the PULCON principle (pulse length based concentration determination). Recovery rates were between 80 % (HMF) and 106 % (ethanol). The limits of quantitation (LOQ) varied between 52 mg/L for saccharin and 12 g/L for sucrose due to different matrix contents. Sample analysis time is about 25 min including sample preparation and automated data processing. A comparison with conventional methods showed the suitability of NMR for routine analysis of soft drinks.
... Numerous parameters were used to assess the quality of edible oils including free fatty acids (FFA), iodine (IV), peroxide (PV) and anisidine value (AV) and various other parameters. Former researches described NMR as a technique extending the analysis of edible oils [1][2][3][4][5][6]. ...
The assessment of quality and authenticity of edible oils is traditionally performed based on several separate analytical methods. These methods were developed and standardized several decades ago undergoing only minor changes since then, which makes oil analysis time-consuming and sometimes even erroneous. A proton nuclear magnetic resonance (1H NMR) spectroscopic method was developed and validated for targeted control of necessary quality parameters (e.g., peroxide, anisidine, acidic and iodine value, fatty acid composition) within short time and in only one analytical run. Additional information about glyceride composition and free fatty acids can be obtained using 13C NMR spectroscopy. The developed method was successfully applied for several edible oil types. Furthermore, multivariate models (principal component analysis and classification methods) based on NMR distribution of major and minor components were developed for screening of type, age, adulteration, and origin of edible oils. Partial least squares regression was applied to correlate NMR profilings with sensory characteristics detected by qualified panels for different types of edible oils. Thus, NMR spectroscopy combining with targeted and non-targeted approaches is a versatile technique, which can be applied for quality and authenticity control of edible oils. NMR method can replace multiple tedious conventional techniques for routine oil analysis.
Food lipid oxidation provides various volatile compounds involved in food flavor via the decomposition of lipid hydroperoxide (LOOH). This study predicted the pathways which can coherently explain LOOH decomposition focusing on hydroperoxy octadecadienoic acid (HpODE) isomers (9-EZ-HpODE, 9-EE-HpODE, 10-HpODE, 12-HpODE, 13-ZE-HpODE, and 13-EE-HpODE) which are the major LOOH contained in edible oils. Each standard was firstly prepared and thermally decomposed. Generated volatile and non-volatile compounds were analyzed by GC-MS and LC-MS/MS. The results showed that all HpODE decomposition was based on the factors such as favorable scission, radical delocalization, and cyclization. Interestingly, the formation of 8-HpODE and 14-HpODE were demonstrated during HpODE decomposition. The insights obtained in this study would explain the generation pathways of flavor involved in food quality.
DFT calculations of δ(13C) and δ(1H) chemical shifts and 3J(13C–O–O–1H) coupling constants of three model hydroperoxides of the naturally occurring cis‐11‐OOH and trans‐9‐OOH isomers of oleate and 9‐cis, 11‐trans‐16‐OOH endo hydroperoxide of methyl linolenate are reported. The computational δ (OOH) for various functionals and basis sets, were found to be nearly identical for the cis/trans geometric isomers. Τhe chemical shifts of the methine CH‐OOH protons and carbons, οn the contrary, are highly diagnostic for the identification of cis/trans geometric isomerism. The chemical shifts of the olefinic protons and carbons strongly depend on the orientation of the hydroperoxide unit relative to the double bond and, thus, of importance in conformational analysis. The results are in very good agreement with the available experimental data. For the various diastereomeric pairs of the model endo‐hydroperoxide, the strongly deshielded OOH resonances, due to the presence of an intramolecular hydrogen bond between the hydroperoxide proton and an oxygen of the endo‐peroxide ring, along with the δ (CH‐OOH), are highly diagnostic for identification and structure elucidation of complex erythro‐ and threo‐ diastereomeric pairs of endo‐hydroperoxides; the computational results are in very good agreement with the available experimental data. The 3J(13C–O–O–1H) coupling constants were found to be < 2 Hz for the cis‐trans geometric models and < 0.5 Hz for the endo‐hydroperoxide and, thus, unimportant in stereochemical analysis. Sharp resonances of the hydroperoxide protons, with Δν1/2 < 3 Hz, are required for the successful implementation of the 1H‐13C HMBC technique.
The formation of linolenic (Ln) and linoleic (L) acyl oxidation products during storage of flaxseed oil (FO)-in-water emulsions was monitored using proton nuclear magnetic resonance (1H NMR) spectroscopy, as well as chemical analytical methods and gas chromatography. Emulsions containing 10% FO and 1% Tween 60 were prepared by homogenization and then stored at 37 °C in the dark for 21 days under accelerated oxidation conditions (500 μmol ferrous sulfate). The induction time of the emulsions, after which rapid lipid oxidation was first observed, was 5-7 days, as shown by increases in peroxide values and hydroperoxide concentrations determined by NMR spectroscopy. Analysis of the hexanal and propanal concentrations during storage by HS-SPME-GC indicated that the oxidation of Ln and L acyls in the emulsions occurred simultaneously. The oxidation products originating from the Ln and L acyls were monitored using 1H NMR spectroscopy throughout the oxidation process. These results also showed that the Ln and L acyls oxidized simultaneously, and isomers of hydroperoxy-cyclic hydroperoxides (HCPs), Z,E-conjugated dienic hydroperoxides (ZECDHPs), and E,E-conjugated dienic hydroperoxides (EECDHPs) were the major primary oxidation products. Aldehydes were observed after 7 days, which was taken to be the start of the propagation stage, with the formation of a significant amount of oxygenated α, β-unsaturated aldehydes (OαβUAs). Based on the concentrations of hydroperoxides originating from the Ln and L acyls, our results suggested that the loss rate of L acyls was parallel to that of Ln acyls. This result was consistent with Ln acyls adopting a tighter packing at the oil-water interface in the emulsions than L acyls. This hypothesis was supported by the NMR relaxation time data. A good correlation between the isomer concentrations of ZECDHPs and HCPs in Ln acyls and between ZECDHPs and EECDHPs in L acyls was shown, with the mole ratios between them being 1.2 and 1.1, respectively. Droplet size and microstructure analyses showed that droplet aggregation occurred from 11 days onwards, which was attributed to polar oxidation products located at the oil droplet surfaces promoting coalescence. Zeta-potential measurements indicated that the droplets became more negative during storage, which was attributed to the accumulation of anionic reaction products at the droplet surfaces.
The fatty acid composition is a parameter that determines the quality and origin of vegetable oils. The standard method used in the analysis of fatty acid composition is gas chromatography (GC). In the last 20 years, however, the ¹H NMR method has become more important in the analysis of fatty acids. Thanks to no need of special sample preparation, the high speed of analysis and the possibility to automate the process of analysis, ¹H NMR is becoming a popular method of testing vegetable oils. It is possible to test oils both qualitatively and quantitatively, taking into account both the fatty acid profile and the level of minor components. In combination with statistical and chemometric methods, the analysis of ¹H NMR spectra allows one to obtain much valuable information about the tested oil, considering its composition, quality, the presence of impurities, or the origin. The paper presents an overview of publications focusing on the application of the ¹H NMR method in the profiling of fatty acids in vegetable oils.
Hemp oil is widely used in the food industry, and also in many other industries. It is characterized by a high content of unsaturated fatty acids with the optimal ratio of ω-6 to ω-3 fatty acids (3:1). Such composition means that this oil is often used in the food, pharmaceutical and cosmetic industries. Due to the popularity of hemp oil and its high content of unsaturated fatty acids, methods for the quick oil quality analysis are sought. Six samples of cold-pressed hemp oil were stored under different conditions (2-8°C and 30°C) for one month and then their ¹H NMR spectra were recorded. The chemometric methods of PCA and OPLS-DA were used to perform the analysis of the spectra. The combination of those methods made it possible to observe the differences in the oil samples after a month of storage. Based on the ¹H NMR spectra, it was possible to differentiate the time and conditions of the oil storage.
Lipid oxidation is one of the main causes of degradation in food emulsions. It leads to the generation of off-flavors and a concomitant reduction in shelf-life of the food products. The multiscale complexity of lipid oxidation reactions in food emulsions has raised the need to develop new methodological approaches. In this chapter, we will discuss how the recent analytical advancements have opened new avenues for the identification and quantification of multiple key oxidation products and for the spatio-temporal resolution of the reactions. After shortly introducing the challenges related to lipid extraction prior to analysis, we will first focus on the use of electron spin resonance for the early assessment and of nuclear magnetic resonance for the simultaneous analysis of multiple oxidation products. Then, we will discuss the potential of chromatographic and mass spectrometry approaches to monitor non-volatile and volatile oxidation products and assess the contribution of minor surface-active lipid species. Finally, the recent developments in electron and fluorescence microscopy to monitor the structural changes associated with lipid oxidation and the localization of the reaction sites in emulsions will be discussed.KeywordsExtractionVolatilesMagnetic resonanceChromatographyMass spectrometryMicroscopyMechanistic insights
Edible oils are indispensable food components, because they are used for cooking or frying. However, during processing, transport, storage, and consumption, edible oils are susceptible to oxidation, during which various primary and secondary oxidative products are generated. These products may reduce the nutritional value and safety of edible oils and even harm human health. Therefore, analyzing the oxidation of edible oil is essential to ensure the quality and safety of oil. Oxidation is a complex process with various oxidative products, and the content of these products can be evaluated by corresponding indexes. According to the structure and properties of the oxidative products, analytical methods have been employed to quantify these products to analyze the oxidation of oil. Combined with proper chemometric analytical methods, qualitative identification has been performed to discriminate oxidized and nonoxidized oils. Oxidative products are complex and diverse. Thus, proper indexes and analytical methods should be selected depending on specific research objectives. Expanding the mechanism of the correspondence between oxidative products and analytical methods is crucial. The underlying mechanism, conventional indexes, and applications of analytical methods are summarized in this review. The challenges and perspectives for future applications of several methods in determining oxidation are also discussed. This review may serve as a reference in the selection, establishment, and improvement of methods for analyzing the oxidation of edible oil.
• Highlights
• The mechanism of edible oil oxidation analysis was elaborated.
• Conventional oxidation indexes and their limited values were discussed.
• Analytical methods for the determination of oxidative products and qualitative identification of oxidized and non-oxidized oils were reviewed.
Rania Ibrahim Mohammad Almoselhy: New Aspects on Stability of some Edible Oils. Unpublished Ph.D Thesis, Department of Food Science, Faculty of Agriculture, Ain Shams University, 2015.
The present study was planned to evaluate the stability of four edible oils namely extra virgin olive oil (EVOO), moringa oil (MO), apricot kernel oil (AKO) and sunflower oil (SO). The oils were analyzed in order to identify the relation between their composition and stability, with great stress to investigate what components are responsible for their stability.
Fourier transform infra red (FTIR) and nuclear magnetic resonance (NMR) spectroscopic determinations were also applied.
MO showed the highest induction period (IP) measured by Rancimat being 190.00 hr indicating superior resistance to oxidation, followed by EVOO (59.11 hr), then AKO (26.00 hr). SO recorded only 7.45 hr. The highest resistance of MO to oxidation followed by EVOO was due to their less linoleate (LO), higher percentage of oleate (OL) and saponifiable matter, as well as antioxidant content of tocopherols, flavonoids, sterols, phenolics, chlorophyll, and carotenoids. In addition, MO contained the highest percentages of stigmasterol, campesterol, Δ5-avenasterol and δ-tocopherol which its antioxidant activity exceeds that of α- and γ-tocopherols and making clear the long IP of this oil. The highest percentages of β-sitosterol was found in EVOO, besides Δ5-avenasterol that may be mainly responsible for olive oil stability, also polyphenols were the main antioxidants in EVOO that approached half of its IP.
AKO with middle IP had relatively high stability due to its higher percentage of OL, but it had higher LO and lower antioxidant content compared to MO and EVOO. The lowest IP of SO was due to its higher PUFA and lower antioxidant content. It seems that β-sitosterol and Δ5-avenasterol were also a main factor in AKO and SO oxidative stability.
From FTIR spectral data of the tested oils, the shift of absorption peak around 3005 cm-1 ordered the oils, where the lowest shift was related to the lowest PUFA and the highest stability which arranged as follows: MO (3003.59 cm-1) ˃ EVOO (3004.55 cm-1) ˃ AKO (3005.52 cm-1) ˃ SO (3006.48 cm-1).
This arrangement reflects the same order of oils stability evaluated by Rancimat method. Also, the higher in intensity of this peak around 3005 cm-1, the higher in USFA From this relation, it was easy to predict the order and the approximate values of the USFA in the oils. When the oil shows a peak around 3470cm-1, it is an indication that the oil is non-oxidized. The chemical shifts of solvent peaks around 2.5 and 3.3 ppm in the 1H-NMR spectra ordered the oils stability, where the lesser shift was corresponded to the oil of higher stability, this order was as obtained by Rancimat; it also agreed with the order of tocopherols content. MO showed the presence of both stigmasterol and β-sitosterol from the signals at 0.662 and 0.784 ppm, respectively. However, EVOO showed a peak at 0.780 ppm assigned to β-sitosterol. Some shifts were denoted in the spectra of the stored oils for 6 months attributed to free fatty acids indicating hydrolytic degradation of acyl groups and the formation of new compounds, as well as conjugated systems. Also, new signals were aroused after 60 months due to different kinds of alcohols, free fatty acids and diglycerides. All the 13C-NMR spectral data from the signals in the four regions of the tested oils, agreed with their GC and the other composition analysis carried out, and reflect the same composition and order of oils stability
obtained by Rancimat method. In addition, its technique is particularly useful in distinguishing between mono-, di-, and triglycerides. In conclusion, FTIR and NMR spectroscopy proved their potency as new analytical methods to investigate the stability of some edible oils and the results obtained agreed with the old common methods of analyses.
*** Keywords: Stability; 1H-NMR spectroscopy; 13C-NMR spectroscopy; FTIR spectroscopy; UV spectroscopy; GC analysis; HPLC analysis; extra virgin olive oil; moringa oil; apricot kernel oil; sunflower oil
*** Suggested Citation:
Almoselhy, Rania I.M., Ph.D. 2015- New Aspects on Stability of some Edible Oils (January 14, 2015). Ain Shams University - Faculty of Agriculture - Department of Food Science, 2015, Available at SSRN: https://ssrn.com/abstract=3908543 or http://dx.doi.org/10.2139/ssrn.3908543
Lipid oxidation is one of the most important factors limiting the shelf life of oils rich in long-chain omega-3 fatty acids and delivery systems because it gives rise to the formation of volatile oxidation products, which will have a negative effect on sensory properties. This chapter summarizes the basic lipid oxidation reactions and also discusses a more complex, integrated reaction scheme including other reactions than formation of lipid hydroperoxides and aldehydes. Finally, the chapter provides an overview of different methods to analyze lipid oxidation products including simple spectrophotometric methods as well as newer advanced, instrumental methods such as NIR, FTIR, NMR, and GC-MS.
Edible oils are prone to oxidation during processing and storage that may negatively affect the oil quality and human health. Determining the peroxide value (PV) of edible oils is essential because PV is one of the most typically used quality parameters to monitor lipid oxidation and control oil quality. Many approaches have been developed to determine the PV of oils. Among them, iodometric titration is the commonly used method for PV determination. Considering the limitations related to titrimetric methods, such as time and environmental concerns, several instrumental techniques have been considered as reliable alternatives. The advantages and limitations of classical titration and instrumental methods are summarized in this review. The prospects and reformative aspects for the future applications of these approaches in PV determination are also discussed.
The present study was planned to evaluate the stability of four edible oils namely extra virgin olive oil (EVOO), moringa oil (MO), apricot kernel oil (AKO) and sunflower oil (SO). The oils were analyzed in order to identify the relation between their composition and stability, with great stress to investigate what components are responsible for their stability.
Fourier transform infra red (FTIR) and nuclear magnetic resonance (NMR) spectroscopic determinations were also applied. MO showed the highest induction period (IP) measured by Rancimat being 190.00 hr indicating superior resistance to oxidation, followed by
EVOO (59.11 hr), then AKO (26.00 hr). SO recorded only 7.45 hr. The highest resistance of MO to oxidation followed by EVOO was due to their less linoleate (LO), higher percentage of oleate (OL) and saponifiable matter, as well as antioxidant content of tocopherols, flavonoids, sterols, phenolics, chlorophyll, and carotenoids. In addition, MO contained the
highest percentages of stigmasterol, campesterol, Δ5-avenasterol and δ-tocopherol which its antioxidant activity exceeds that of α- and γ-tocopherols and making clear the long IP of this oil. The highest percentages of β-sitosterol was found in EVOO, besides Δ5-avenasterol that may be mainly responsible for olive oil stability, also polyphenols
were the main antioxidants in EVOO that approached half of its IP.
AKO with middle IP had relatively high stability due to its higher percentage of OL, but it had higher LO and lower antioxidant content compared to MO and EVOO. The lowest IP of SO was due to its higher PUFA and lower antioxidant content. It seems that β-sitosterol and Δ5-avenasterol were also a main factor in AKO and SO oxidative stability.
From FTIR spectral data of the tested oils, the shift of absorption peak around 3005 cm-1 ordered the oils, where the lowest shift was related to the lowest PUFA and the highest stability which arranged as follows: MO (3003.59 cm-1) ˃ EVOO (3004.55 cm-1) ˃ AKO (3005.52 cm-1) ˃ SO (3006.48 cm-1).
This arrangement reflects the same order of oils stability evaluated by Rancimat method. Also, the higher in intensity of this peak around 3005 cm-1, the higher in USFA From this relation, it was easy to predict the order and the approximate values of the USFA in the oils. When the oil shows a peak around 3470cm-1, it is an indication that the oil is non-oxidized.
The chemical shifts of solvent peaks around 2.5 and 3.3 ppm in the 1H-NMR spectra ordered the oils stability, where the lesser shift was corresponded to the oil of higher stability, this order was as obtained by Rancimat; it also agreed with the order of tocopherols content. MO showed the presence of both stigmasterol and β-sitosterol from the signals at 0.662 and 0.784 ppm, respectively. However, EVOO showed a peak at 0.780
ppm assigned to β-sitosterol. Some shifts were denoted in the spectra of the stored oils for 6 months attributed to free fatty acids indicating hydrolytic degradation of acyl groups and the formation of new compounds, as well as conjugated systems. Also, new signals were aroused after 60 months due to different kinds of alcohols, free fatty acids and diglycerides.
All the 13C-NMR spectral data from the signals in the four regions of the tested oils, agreed with their GC and the other composition analysis carried out, and reflect the same composition and order of oils stability obtained by Rancimat method. In addition, its technique is particularly useful in distinguishing between mono-, di-, and triglycerides.
In conclusion, FTIR and NMR spectroscopy proved their potency as new analytical methods to investigate the stability of some edible oils and the results obtained agreed with the old common methods of analyses.
Edible oils oxidize during microwave heating, which may affect their nutritional value and safety. Exploring the oxidation mechanisms of unsaturated fatty acids in edible oils to determine which are suitable for microwave heating is therefore important. We used GC-MS, low-field NMR, and ¹H NMR techniques to study functional-group oxidation, the unsaturated fatty acid change law, and the distribution and migration of protons in various functional groups of four common vegetable cooking oils during microwave treatment. We show that the acid values of sunflower, soybean, peanut, and corn oil increased by 14%, 31%, 36%, and 101%, respectively, while the concentrations of malondialdehyde increased by 115%, 664%, 158%, and 333%, respectively, and the peroxide value fluctuated with increasing microwave power. The C16:0 concentrations of all four edible oils increased by more than 50%, and the concentration of polyunsaturated fatty acids decreased by more than 30% during microwave treatment; hence sunflower oil is the most suitable of the above-mentioned oils for daily microwave heating. In addition, we recommend the use of three characteristic functional groups to monitor the oxidative changes undergone by oils: olefinic H (CH = CH), diallyl CH2 (CH = CH–CH2–CH = CH), and allyl CH2 (CH = CH–CH2).
The oxidation of cold-pressed and commercial refined camellia oil stored at room temperature for one year was comparatively studied by ¹H and ³¹P NMR spectroscopy. The oxidation of extra virgin olive oil (EVOO) under the same conditions was further compared. The ¹H NMR showed that no aldehydes were formed in the studied period. Coupled with the changes of unsaturated acyl groups, the oxidation degrees of the three oils could be obtained follow the order: commercial refined camellia oil > cold-pressed camellia oil > EVOO. The ³¹P NMR showed that the evolution of diacylglycerols (DGs) and ratio D in commercial refined camellia oil was fairly different from other two oils. Besides, the kinetics curves of unsaturated acyl groups and ratio D both fit to an exponential equation with high coefficients which indicated that the oxidation of the studied oils progressed in an exponential way with storage time at room temperature.
Using the universal calibration and the Mark‐Houwink equation (MHE) (), three batches of oleic estolide acids and their corresponding 2‐ethylhexyl esters were characterized using gel permeation chromatography (GPC). The MHE parameters in tetrahydrofuran (THF) at 40 °C were determined (for acids: α = 0.442 ± 0.003 and log10K=2.505 ± 0.007, for esters: α =0.531 ± 0.006 and log10K =2.794 ± 0.018). The fits of the GPC chromatograms yielded also the oligomeric composition of the estolides, which can be used to calculate the estolide number (EN) of an estolide mixture, and other molecular‐weight distribution parameters, such as number‐average molecular weight ( M n), weight‐average molecular weight ( M w), and dispersity (Ð). Using the Deming line fit, we concluded that the GPC should be expected to be approximately three times more sensitive than the currently used methods for determination of EN values.
Proton nuclear magnetic resonance ( ¹ H NMR) combined with partial least squares (PLS) was developed for the rapid determination of squalene and sterols (brassicasterol, campesterol, stigmasterol and β-sitosterol) in 119 vegetable oils from 7 different species. The ¹ H NMR spectra of these oil samples were correlated to the reference value determined by gas chromatography-mass spectrometry (GC–MS) method by PLS regression, using outlier removal, selection of input X-variables and data pretreatments. Auto-scaling (UV) was chosen as the best pre-processing for the PLS models of stigmasterol, β-sitosterol, and squalene. Pareto variance (Par) was more suitable for the PLS model of brassicasterol. The model for squalene was further improved by a reduced number of variables with variable importance for the projection (VIP) scores technique. The study demonstrated the potential application of NMR coupled with PLS as a rapid and nondestructive technique for the routine analysis of squalene and sterols in vegetable oils.
Multinuclear and multidimensional NMR spectroscopy was applied as a robust and rapid tool for the analysis of several classes of non-polar compounds in roasted coffee beans, coffee beverage and spent coffee grounds. In addition to various fatty acids, other compounds found in roasted coffee lipids, include oxidation and hydrolysis products, terpenes, sterols, and phospholipids. Spent coffee grounds have a similar fatty acid composition with roasted coffee beans and they are rich in Cafestol and Kawheol, which appear as esters of fatty acids. Triglycerides extracted from coffee waste using a green chemistry approach, based on supercritical CO2 extraction, are promising candidates for the production of bioplastics. Bioplastic precursors were produced using an in situ solvent-free epoxidation process and the reaction monitoring was performed using NMR spectroscopy.
Fish oil is becoming increasingly popular as a dietary supplement as well as for its use in animal feed, which is mainly due to its high contents of the health promoting omega-3 fatty acids. However, these polyunsaturated fatty acids are highly susceptible to oxidation, which results in a decrease of the fish oil quality. This study investigated the potential of ¹H NMR, FT-MIR, and FT-NIR spectroscopy in the quality assessment of fish oils. A total of 84 different fish oils, of which 22 were subjected to accelerated storage with varying temperature and light exposure, were used to develop models for predicting the peroxide value (PV), the anisidine value (AnV), and the acid value (AV). Predictions were based on comprehensive spectroscopic data in combination with Artificial Neural Networks (ANN) as well as Partial Least Squares Regression (PLSR). The best ANN model for PV was obtained from NMR data, with a predictive coefficient of determination (Q²) of 0.961 and a Root Mean Square Error of Prediction (RMSEP) of 1.5 meq O2 kg− 1. The combined MIR/NIR data provided the most reliable ANN model for AnV (Q² = 0.993; RMSEP = 0.74). For AV, the ANN model based on the MIR data yielded a Q² of 0.988 and an RMSEP of 0.43 mg NaOH g− 1. In most cases, the accuracy of the ANN models was superior to the respective PLSR models. Variable selection and data dimensionality reduction turned out to improve the performance of the ANN models in some cases. The application of ¹H NMR, FT-MIR, and FT-NIR spectroscopy in combination with ANN can be considered very promising for a rapid, reliable, and sustainable assessment of fish oil quality.
The oxidative degradation of omega-3 fatty acids-rich fish oil was investigated by ¹H Nuclear Magnetic Resonance (NMR) Spectroscopy. The intensities of key distinct spectral signals corresponding to bis-allylic (RBAG) and terminal methyl groups (RO3TG) from omega-3 fatty acid residues were monitored in relation to the sn-2 glycerol peak from triacylglycerols, in fish oil oxidized under various conditions. Under oxygen-rich conditions and accelerated oxidation, RBAG and RO3TG decreased sharply over time, whereas under oxygen-limited conditions, they remained unchanged throughout the entire length of the storage, demonstrating that the method has a practical applicability for comparing storage conditions and antioxidants behaviors. At ambient temperature and limited oxygen availability, the NMR indicators declined steadily only after the initial period in which they increased. It was hypothesized that sn-2 hydrolysis followed by initiation of oxidation via electron transfer and decarboxylation may be responsible for these observations.
Lipid oxidation can lead to flavor and safety issues in fat-containing foods. In order to measure the extent of lipid oxidation, hydroperoxides and their scission products are normally targeted for analytical purposes. In recent years, the formation of rarely monitored oxygenated products, including epoxides, alcohols, and ketones, has also raised concerns. These products are thought to form from alternative pathways that compete with chain scissions, and should not be neglected. In this review, a number of instrumental techniques and approaches to determine epoxides, alcohols, and ketones are discussed, with a focus on their selectivity and sensitivity in applications to food lipids and oils. Special attention is given to methods employing gas chromatography (GC), high-performance liquid chromatography (HPLC), and nuclear magnetic resonance (NMR). For characterization purposes, GC-mass spectrometry (GC-MS) provides valuable information regarding the structures of individual oxygenated fatty acids, typically as methyl esters, isolated from oxygenated triacylglycerols (TAGs), while the use of liquid chromatography-MS (LC-MS) techniques allows analysis of intact oxygenated TAGs and offers information about the position of the oxygenated acyl chain on the glycerol backbone. For quantitative purposes, traditional chromatography methods have exhibited excellent sensitivity, while spectroscopic methods, including NMR, are superior to chromatography for their rapid analytical cycles. Future studies should focus on the development of a routine quantitative method that is both selective and sensitive.
Spectroscopic techniques utilizing FTIR, ¹H and ¹³C NMR spectral fingerprints of the neat oils, as well as standard titrimetric and GC–MS analyses were all employed to determine the quality parameters and fatty acid (FA) profiles for Soxhlet-extracted seed oils of four indigenous plants from Botswana: Tylosema esculentum (morama), Schinziophyton rautanenii (mungongo), Citrullus lanatus (kgengwe) and Bauhinia petersiana (mogose). The physicochemical parameters and FA composition obtained from spectroscopic methods were found to be similar to those obtained from classical procedures indicating that oil quality parameters can reliably be obtained from spectroscopic data. The FA analysis showed the presence of 73–84% unsaturated FAs in the four seed oils. In addition, spectroscopic data clearly established the presence of the uncommon tri-unsaturated FA, α-eleostearic acid (α-ESA) in mungongo seed oil which was quantified as 25% by ¹³C NMR. Generally, the high levels of unsaturated FAs in the oils indicate their suitability in health food supplements.
Industrial relevance
The four plants studied are highly treasured in the areas where they grow due to the fact that they have for centuries provided food security, and means of livelihood for populations living in the Kalahari Desert and other marginal regions of the southern Africa region. Currently, there is a drive to add value to such often underutilized plants to aid in poverty alleviation by processing and marketing the products as healthy food supplements or cosmetic formulations. To this end, reliable methods for characterization and comparison of the FA composition of the seed oils from different geographical locations is required. The development of rapid, non-destructive spectroscopic techniques that can be applied directly on the neat oils is therefore an important venture.
Nuclear Magnetic Resonance (NMR) spectroscopy has been mainly used for the elucidation and confirmation of structures. For the last decade, cryogenic probe technology has opened a wide door for routine analysis due to an increase of the signal to noise ratio by a factor of 5. NMR methods have been introduced to quantitative analysis in any composition of lipids. Any NMR analysis of a system of lipids is a multi-component analysis, even for purified components like Triacylglycerol (TAG) or single isolated Polar Lipids (PLs), due to the natural individual Fatty Acid (FA) composition. Because NMR is an absolute molar method, it is possible that within one analysis each chemical compound in a mixture can be quantified as long as the four principles are fulfilled. This is valid for the intra-molecular FA distribution as well as for mixtures of lipid classes. The most powerful method in PL analysis is 31Phosphorus NMR (31P NMR) spectroscopy. This method differentiates between the various PLs and has high dynamics in quantification. Only phosphorus-containing substances are detected by the method; the analysis is not disturbed by other non-phosphorus components. The resonance frequency of phosphorus depends on the chemical environment within the molecule. PLs with different chemical structures are, therefore, recorded at distinct frequencies.
The consumption of fish oil-based dietary supplements has increased dramatically in recent years, which is mainly due to their high content of health promoting omega-3 fatty acids. However, these polyunsaturated fatty acids are extremely prone to oxidation. This study investigated the potential of 1H NMR spectroscopy for the assessment of the oxidative deterioration of fish oils. Nine raw fish oils of different fish species were stored for 3 months at room temperature at different degrees of sunlight exposure as well as under standardized accelerated storage conditions for 6 days (at 40°C and under constant light exposure). Fish oil samples were analyzed by 1H NMR spectroscopy as well as by traditional methods to determine the fat quality parameters peroxide value (PV), anisidine value (AnV), TOTOX value, and acid value (AV). PLS (partial least squares) regression models were used to predict these fat quality parameters based on the 1H NMR spectra. The best regression models reached an R2 of 0.949, 0.962, 0.991, and 0.977 for PV, AnV, TOTOX value, and AV, respectively. In conclusion, 1H NMR spectroscopy is a promising approach for a fast, reliable, and sustainable assessment of fish oil quality with regard to lipid oxidation. Practical applications: The results indicate a great potential of 1H NMR spectroscopy in the quality assessment of fish oils. This technology requires little time, work, amount of sample, and solvent and provides extensive information that can be obtained from a single spectrum. Such an approach is significantly more specific and detailed than traditional lipid oxidation parameters. Nine raw fish oils are stored under different conditions and analyzed by 1H NMR spectroscopy as well as by traditional methods to determine the lipid quality parameters peroxide value, anisidine value, TOTOX value, and acid value. Subsequently, PLS regression models are generated to predict these indices from the NMR spectra.
Methyl esters of C20-22 n-3 polyunsaturated fatty acids derived from sardine oil triglycerides were concentrated to 86% purity with greater than 30% recovery by argentated chromatography. The synergistic effect of ethyl acetate fractions of seaweeds Kappaphycus alvarezii, Hypnea musciformis and Jania rubens used in 0.1:0.2:0.2 (%, w/w) ratio in arresting oxidative degradation of the n-3 PUFA methyl ester concentrate was demonstrated during accelerated storage. The induction time (6.8 h) and antioxidant activity indices (>24) were greater for n-3 PUFA concentrates supplemented with seaweed extracts than antioxidants BHT and α-tocopherol (<5 h and <17, respectively). Nuclear Magnetic Resonance spectroscopy was employed to study the oxidative changes of fatty acid signals of PUFA concentrate during accelerated storage. Potential of seaweeds to improve the storage stability of C20-22 n-3 fatty acid methyl esters was studied. This study has applications in development of food and pharmaceutical products.
1H nuclear magnetic resonance (1H NMR) was used to determine the effect of positional distribution of linoleic acid (L) on the oxidative stability of triacylglycerols. For this purpose, structured soybean oil (SSO), which had a similar total fatty acid composition but a different L positional distribution than soybean oil (SO), was produced by interesterification reaction. The SO and SSO were oxidized in the dark at 40 °C. Afterwards, 1H NMR was used to monitor the oxidation process and quantify the main polyunsaturated fatty acid, Z,E- and E,E-conjugated forms, hydroperoxides, and aldehydes at different oxidation periods in a single run. After 45 days of oxidation, SSO showed lower L content than SO (9.9 ± 1.1 and 16.8 ± 0.5 %, respectively). Additionally, secondary oxidation products in SSO were shown to be more abundant than in SO (82.3 ± 4.9 and 43.6 ± 0.9 mmol/L oil, respectively). This study indicated that SO, which contains a higher distribution of L at the sn-2 position, was more resistant to autoxidation than SSO.
In this paper, oleuropein and some other related phenolic compounds are reviewed. Their occurrence, distribution, biosynthesis and transformation during maturation and during industrial processing (preparation of table olives and oil production) are described. Their role in human health is proposed based on current human, animal and in vitro studies as molecules with antioxidant and antimicrobial properties.© 2000 Society of Chemical Industry
Biologically active ingredients and excipients are the essentials of a drug formulation, such as a tablet, dragee, solution,
etc. Quality control of such substances thus plays a pivotal role in the production process of pharmaceutical drugs. Since
these agents often exhibit complex structures, consist of multiple components, or lack of a chromophore, traditional means
of characterization are often not feasible. Furthermore, substances of small molecular weight or strong polar character generally
exhibit poor chromatographic properties, thus, conventional procedures such as high-performance liquid chromatography are
often not applicable. Instead, quantitative nuclear magnetic resonance (qNMR) spectroscopy has emerged as an alternative or
orthogonal method in drug analysis. In this review, we elaborate on the application of qNMR to three important classes of
biological substances, namely polysaccharides, amino acids, and lipids, and demonstrate the benefits of this modern tool in
contrast to traditional techniques.
KeywordsQuantitative NMR spectroscopy–European pharmacopoeias–Active pharmaceutical ingredients–Heparin–Amino acid–Lipid
The hydroperoxides and secondary products formed from trilinoleoylglycerol autoxidized at 40°C were isolated and characterized
to clarify their contribution to oxidative deterioration of vegetable oils. The products were purified by high performance
liquid chromatography (HPLC) and identified, as intact triacylglycerols, by ultraviolet, infrared,1H NMR and13C NMR analyses, and after derivatization by lipolysis, gas chromatography, and gas chromatography-mass spectrometry. The main,
primary products included mono-,bis- and tris-9-hydroperoxy-trans-10,cit-12-; 9-hydroperoxy-trans-10,trans-12; 13-hydroperoxy-cis-9,trans-11; and 13-hydroperoxy-trans-9,trans-11-linolenoyl glycerols. The structures of the minor secondary products analyzed after derivatization were consistent with
known oxidative degradation products of linoleate hydroperoxides. HPLC analyses showed that thebis- and tris-hydroperoxides were formed from the mono-hydroperoxides during autoxidation at peroxide values above 18 and 28
meq/kg. Studies on the further oxidation of the mono-hydroperoxides support a mechanism for the consucutive formation ofbis- and tris-hydroperoxides from the monohydroperoxides. HPLC analyses showed that no preferential oxidation occurred between
the 1(3)- and 2-triglyceride positions. Hydroperoxides of linoleate triacylglycerols may be important precursors of volatile
compounds contributing to off-flavors of vegetable oils.
The hydroperoxides and secondary products formed from trilinolenoylglycerol autoxidized at 40°C were isolated and characterized
to clarify the mechanism of oxidative deterioration of polyunsaturated vegetable oils. The products were purified by high
performance liquid chromatography (HPLC) and identified either as intact triacylglycerols spectrophotometrically, or after
lipolysis (pancreatic lipase) and capillary gas chromatography and gas chromatography-mass spectrometry. The products included
9-, 12-, 13-, and 16-mono-,bis-, tris-hydroperoxy, 9- and 16-hydroperoxy epidioxy, 9- and 16-hydroperoxy bicycloendoperoxy and 9,12-, 13,16-, and 9,16-dihydroperoxy
linolenoylglycerols. The mono-hydroperoxides and sydroperoxy epidioxides were the only main products initially formed at peroxide
values (PV) below 30.Bis- and tris-hydroperoxides were formed consecutively as minor products from the mono-hydroperoxides at PV's between 31 and
47. Hydroperoxy bicycloendoperoxides and monodihydroperoxides were also formed as minor secondary products at PV's above 75.
HPLC analyses show a small preference for the formation of 16-hydroperoxides on the 1(3)-position over the 2-position of trilinolenoylglycerol.
However, there was no selectivity for the formation of the 9-, 12- and 13-hydroperoxides and for the hydroperoxy epidioxides
between the 1(3)- and the 2-positions in trilinolenoylglycerol. Mono-hydroperoxides and hydroperoxy epidioxides of linolenate
triacylglycerols may be important precursors of volatile compounds contributing to oxidative deterioration of vegetable oils.
The role of Quantitative NMR (qNMR) spectroscopy in pharmaceutical applications are discussed. qNMR is linear over a wide concentration range and it seems to be more robust than the separation methods coupled to UV, fluorescence, CAD, NQAD, and ELSD. It requires minimal sample preparation and a readily available internal standard (IS). Simultaneous determination of content, detection of impurities, residual solvents and other additives is possible as long as a component contains the nucleus observed. While the pharmaceutical companies extensively apply qNMR in drug discovery and development they mostly use HPLC in routine quality analysis rather than qNMR. Recently, qNMR became the leading method for the purity analysis of unfractionated heparin sodium and calcium in the USP which was deliberately contaminated with anaphylactoid oversulfated chondroitin sulphate (OSCS). qNMR should be considered more often for quantification and quality control of drugs, excipients, agrochemicals, and food ingredients.
The oxidative deterioration of glycerol-bound polyunsaturated fatty acids (PUFAs) in culinary oils and fats during episodes of heating associated with normal usage (30-90 min at 180 degrees C) has been monitored by high field 1H NMR spectroscopy. Thermal stressing of PUFA-rich culinary oils generated high levels of n-alkanals, trans-2-alkenals, alka-2,4-dienals and 4-hydroxy-trans-2-alkenals via decomposition of their conjugated hydroperoxydiene precursors, whereas only low concentrations of selected aldehydes were produced in oils with a low PUFA content, lard and dripping when subjected to the above heating episodes. Samples of repeatedly used, PUFA-rich culinary oils obtained from restaurants also contained high levels of each class of aldehyde. The dietary, physiological and toxicological ramifications of the results obtained are discussed.
We reviewed the bioavailability and antioxidant effects of phenols from extra virgin olive oil.
We searched the MEDLINE database for the years 1966-2002. To review the bioavailability of olive oil phenols, we selected animal and human studies that studied the absorption, metabolism, and urinary excretion of olive oil phenols. We also estimated the intake of the various phenols in the Mediterranean area. To review the antioxidant effects of olive oil phenols, we included human and animal studies on the effect of olive oil phenols on markers of oxidative processes in the body. We excluded studies without a proper control treatment and studies in which the antioxidant effects of phenols could not be disentangled from those of the fatty acid composition of olive oil.
Bioavailability studies in humans show that the absorption of olive oil phenols is probably larger than 55-66 mol%, and that at least 5% is excreted in urine as tyrosol and hydroxytyrosol. Animal studies suggest that phenol-rich olive oil lowers oxidisability of ex vivo low-density lipoprotein (LDL) particles or lowers markers in urine of oxidative processes in the body. In five out of seven human studies, however, these effects of phenols were not found. There are no data on the phenol concentrations in plasma that are attainable by intake of olive oil. We estimated that 50 g of olive oil per day provides about 2 mg or approximately 13 micromol of hydroxytyrosol-equivalents per day, and that the plasma concentration of olive oil phenols with antioxidant potential resulting from such an intake can be at most 0.06 micromol/l. This is much lower than the minimum concentrations of these phenols (50-100 micromol) required to show antioxidant activity in vitro.
Although phenols from olive oil seem to be well absorbed, the content of olive oil phenols with antioxidant potential in the Mediterranean diet is probably too low to produce a measurable effect on LDL oxidisability or other oxidation markers in humans. The available evidence does not suggest that consumption of phenols in the amounts provided by dietary olive oil will protect LDL against oxidative modification to any important extent.
The essential oil of black cumin seeds, Nigella sativa L., was tested for a possible antioxidant activity. A rapid evaluation for antioxidants, using two TLC screening methods, showed that thymoquinone and the components carvacrol, t-anethole and 4-terpineol demonstrated respectable radical scavenging property. These four constituents and the essential oil possessed variable antioxidant activity when tested in the diphenylpicrylhydracyl assay for non-specific hydrogen atom or electron donating activity. They were also effective ·OH radical scavenging agents in the assay for non-enzymatic lipid peroxidation in liposomes and the deoxyribose degradation assay.
Hydrophilic phenols are the most abundant natural antioxidants of virgin olive oil (VOO), in which, however, tocopherols and carotens are also present. The prevalent classes of hydrophilic phenols found in VOO are phenolic alcohols, phenolic acids, flavonoids, lignans and secoiridoids. Secoiridoids including aglycon derivatives of oleuropein, demethyloleuropein and ligstroside, that are present in olive fruit, are the most abundant phenolic antioxidants of VOO. In this paper, the phenolic composition of VOO as well as the agronomic and technological parameters that affect their concentration in the oil are discussed. The olive cultivar and the ripening stage of fruit, in fact, have always been the most studied agronomic aspects that affect phenolic concentration in VOO. However, the malaxation conditions and the extraction systems used to separate oil from olive pastes (i.e. pressure three-phases and two-phases centrifugation systems) are also of great importance.
Lipid oxidation includes a complex set of chemical reactions; and no single analytical method is available to give a satisfactory
description of lipid oxidation status. High-resolution NMR spectroscopy techniques were tested to establish possible correlations
with traditional analytical methods and to study lipid oxidation products. Ethyl esters of all-cis 4,7,10,13,16,19-docosahexaenoic acid (DHA) (22∶6n−3), with and without added α-tocopherol, were oxidized in the dark at 25°C
in an air-circulating oven. Correlations were found between primary oxidation products (PV and conjugated dienes) and the
appearance of peaks in the 8.0–10.5 ppm chemical shift region of the 1H NMR spectra. Multivariate data analysis (partial least squares; principal component regression) and the study of specific
regions of the spectra obtained made it possible to easily separate samples of esters with and without α-tocopherol based
on the oxidation products formed. Based on knowledge about lipid oxidation products formed in marine lipids, selected oxidation
products have been studied in the 1H NMR spectra with the aim of finding detection limits and their chemical shift values.
This IUPAC nomenclature document has been prepared to establish a uniform and meaningful approach to terminology, notation, and formulation for calibration in analytical chemistry. In this first part, general fundamentals of calibration are presented, namely for both relationships of qualitative and quantitative variables (relations between variables characterizing certain types of analytes and measured signals in certain positions of a measured function on the one hand and between variables characterizing the amount or concentration of the chemical species and the intensities of the measured signals, on the other hand). On this basis, the fundamentals of the common single component calibration which models the relationship y = f(x) between the signal intensities y and the amounts or concentrations x of the analyte under given conditions are represented. Additional papers will be prepared dealing with extensive relationships between several signal intensities and analyte contents, namely with multivariate calibration and with optimization and experimental design. © 1998, Walter de Gruyter GmbH, Berlin/Boston. All rights reserved.
Calibration in analytical chemistry refers to the relation between sample domain and measurement domain (signal domain) expressed by an analytical function x = fs(Q) representing a pattern of chemical species Q and their amounts or concentrations x in a given test sample on the one hand and a measured function y = f(z) that may be a spectrum, chromatogram, etc. Simultaneous multispecies analyses are carried out mainly by spectroscopic and chromatographic methods in a more or less selective way. For the determination of n species Qi (i = 1,2...n), at least n signals must be measured which should be well separated in the ideal case. In analytical practice, the situation can be different.
The mechanism of methyl oleate autoxidation was investigated. HPLC techniques were developed to analyze the products of autoxidation (hydroperoxides and the corresponding alcohols). The alcohols could be completely resolved by normal-phase chromatography, six products being characterized having oxygen substitution and double position as follows: 11-OOH-trans-Delta(9-10), 11-OOH-cis-Delta(9-10), 10-OOH-trans-Delta(8-9), 9-OOH-trans-Delta(10-11), 8-OOH-trans-Delta(9-10), 8-OOH-cis-Delta(9-10) As the hydrogen atom donor concentration of the medium of autoxidation is increased, increased 11-cis, 8-cis, 9-trans, and 10-trans hydroperoxides and decreased 11-trans and 8-trans hydroperoxides were obtained, consistent with a mechanism in which peroxyl H-atom abstraction and [2,3] allylperoxyl rearrangement are in competition. An iterative computer kinetic analysis was developed which modeled the oleate autoxidation mechanism, and rearrangement rate constants were determined. Allylperoxyl radicals undergo rearrangement with different rates depending on the geometry of the allylperoxyl.
The aim of this study was to investigate whether hydroperoxides are formed in the autoxidation of conjugated linoleic acid (CLA) methyl ester both in the presence and absence of -tocopherol. The existence of hydroperoxide protons was confirmed by D2O exchange and by chemoselective reduction of the hydroperoxide groups into hydroxyl groups using NaBH4. These experiments were followed by nuclear magnetic resonance (NMR) spectroscopy. The 13C and 1HNMR spectra of a mixture of 9-hydroper-oxy-10-trans,12-cis-octadecadienoic acid methyl ester (9-OOH) and 13-hydroperoxy-9-cis, 11-trans-octadecadienoic acid methyl ester (13-OOH), which are formed during the autoxidation of methyl linoleate, were studied in detail to allow the comparison between the two linoleate hydroperoxides and the CLA methyl ester hydroperoxides. The 13CNMR spectra of samples enriched with one of the two linoleate hydroperoxide isomers were assigned using 2D NMR techniques, namely Correlated Spectroscopy (COSY), gradient Heteronuclear Multiple Bond Correlation (gHMBC), and gradient Heteronuclear Single Quantum Correlation (gHSQC). The 13C and 1H NMR experiments performed in this study show that hydroperoxides are formed during the autoxidation of CLA methyl ester both in the presence and absence of -tocopherol and that the major isomers of CLA methyl ester hydroperoxides have a conjugated monohydroperoxydiene structure similar to that in linoleate hydroperoxides.
In a major pathway of the autoxidation of methyl linolenate, peroxyl radicals of the internal hydroperoxides undergo rapid 1,3-tyclisation to form hydroperoxyepidioxides. Because linolenate hydroperoxides are relatively unstable, free radical antioxidants are much less effective in linolenate oils than in linoleate oils. Tocopherols and carotenoids effectively inhibit photosensitised oxidation of vegetable oils. Direct gas chromatographic analyses of malonaldehyde do not correlate with the TBA test. Model fluorescence studies indicate that malonaldehyde may not be so important in crosslinking with DNA. In contrast to oxidised methyl linoleate, oxidised trilinolenin does not form dimers. Although trilinolein oxidises with no preference between the 1(3)-and 2-triglyceride positions, the n-3 double bond of trilinolenin oxidises more in the 1(3)- than in the 2-position. Synthetic triglycerides oxidise in the following decreasing relative rates: LnLnL, LnLLn, LLnL, LLLn (Ln = linolenic and L = linoleic). To estimate the flavour impact of volatile oxidation products their relative threshold values must be considered together with their relative concentration in a given fat.
Previous work in our laboratory demonstrated that soybean oil oxidation, expressed as PV, can be determined using NIR transmission
spectroscopy as an alternative to the official AOCS iodometric titration method. In the present study, a comparison of four
peroxide analytical methods was conducted using oxidized soybean oil. The methods included the official AOCS iodometric titration,
the newly developed NIR method, the PeroxySafe™ kit, and a ferrous xylenol orange (FOX) method, the latter two being colorimetric methods based on oxidation of iron. Five
different commercially available soybean oils were exposed to fluorescent light to obtain PV levels of 0–20 meq/kg; periodic
sampling was done to ensure having representative samples throughout the designated range. A total of 46 oil samples were
analyzed. Statistical analysis of the data showed that the correlation coefficient (r) and standard deviation of differences (SDD) between the standard titration and NIR methods were r=0.991, SDD=0.72 meq/kg; between titration and the PeroxySafe™ kit were r=0.993, SDD=0.56 meq/kg; and between the standard titration and FOX method were r=0.975, SDD=2.3 meq/kg. The high correlations between the titration, NIR, and PeroxySafe™ kit data indicated that these methods were equivalent.
Oxidative stability of oils extracted from intact and dehulled sesame seeds was determined by monitoring changes in fatty
acid composition, iodine value (IV), peroxide value (PV), conjugated diene (CD), para-anisidine value (p-AV), and 2-thiobarbituric acid (TBA) value and by nuclear magnetic resonance spectroscopy after storage under Schaal oven
conditions at 65°C for up to 35 d. The oils from coated seeds were more stable, as reflected in PV, CD, p-AV and TBA values, than those extracted from dehulled seeds after roasting at 200°C, steaming at 100°C, roasting at 200°C
plus steaming, or microwaving at 2450 MHz, except for TBA values of oil from microwaved seeds. After 35 d of storage at 65°C,
the CD, p-AV, and TBA values of extracted oil from dehulled microwaved seeds were 17.72, 10.20, and 1.22, respectively, while those
of their coated counterparts were significantly (P<0.05) different at 14.20, 16.47, and 1.26, respectively. Few significant changes were evident in the fatty acid composition
of oil obtained from either coated and dehulled seeds subjected to different treatments. Nuclear magnetic resonance analyses
found that Rao (aliphatic to olefinic protons) and Rad (aliphatic to diallylmethylene protons) ratios increased steadily over the entire storage period, which indicated progressive
oxidation of unsaturated fatty acids.
Subjection of polyunsaturated fatty acid (PUFA)-rich culinary oils to standard frying episodes generates a range of lipid
oxidation products (LOP), including saturated and α,β-unsaturated aldehydes which arise from the thermally induced fragmentation
of conjugated hydroperoxydiene precursors. Since such LOP are damaging to human health, we have employed high-resolution,
two-dimensional 1H-1H relayed coherence transfer, 1H-1H total correlation, 1H-13C heteronuclear multiple quantum correlation, and 1H-1H J-resolved nuclear magnetic resonance (NMR) spectroscopic techniques to further elucidate the molecular structures of these
components present in (i) a model linoleoylglycerol compound (1,3-dilinolein) allowed to autoxidize at ambient temperature
and (ii) PUFA-rich culinary oils subjected to repeated frying episodes. The above techniques readily facilitate the resolution
of selected vinylic and aldehydic resonances of LOP which appear as complex overlapping patterns in conventional one-dimensional
spectra, particularly when employed in combination with solvent-induced spectral shift modifications. Hence, much useful multi-component
information regarding the identity and/or classification of glycerol-bound conjugated hydroperoxydiene and hydroxydiene adducts,
and saturated and α,β-unsaturated aldehydes, present in autoxidized PUFA matrices is provided by these NMR methods. Such molecular
information is of much value to researchers investigating the deleterious health effects of LOP available in the diet.
High-resolution 1H nuclear magnetic resonance (1H NMR) has been found to be an effective tool for the direct, rapid, and automated determination of the iodine value (IV)
of vegetable oils, including hydrogenated oils (IV=45.9–140.2). The total time required to obtain the 1H NMR data is about 3 min per sample. The IV is calculated from the number of double-bonded protons and the average molecular
weight derived directly from the spectrum. The average of olefinic protons and allylic plus divinyl protons area was used
to calculate the absolute number of double-bonded protons. The 1H NMR results were compared with those obtained by the traditional Wijs-cyclohexane methods. The correlation coefficient between
traditional IV and the novel 1H NMR method was r
2=0.9994 for the regression equation Y=0.9885X + 2.8084, where X was the result given by the traditional method. With the proposed regression equation, IV calculated by the 1H NMR method was within an error of ± 1 unit of the result obtained by the traditional method. The proposed method is practically
viable if one can afford to have the NMR system.
The oil liquid matrix of several corn oil samples that have been stored at room temperature in closed receptacles for different periods of time is studied by means of 1H nuclear magnetic resonance (1H NMR), in order to further knowledge about this type of edible oil oxidation. As expected, the degradation of linoleic acyl groups predominates. In samples at early oxidation stages the presence of hydroperoxides and of (Z,E) conjugated-dienic systems is demonstrated, the concentration of the first group being higher than that of the second. In addition to these compounds, the presence of hydroxy derivatives supporting (Z,E) conjugated-dienic systems, as well as of hydroperoxy derivatives supporting (E,E) conjugated-dienic systems, in samples at intermediate and advanced oxidation stages, is also shown. Corn oil samples at advanced stages of oxidation also contain aldehydes, among which there are alkanals, (E)-2-alkenals, (E,E)-2,4-alkadienals, 4-hydroxy-(E)-2-alkenals, 4-hydroperoxy-(E)-2-alkenals and 4,5-epoxy-(E)-2-alkenals. The concentrations of the different kinds of intermediate compounds above mentioned as well as of the different kinds of aldehydes present in the oil liquid matrix were determined. These latter compounds can be either free or joined to truncated structures of triglycerides. In addition, a principal component analysis between storage conditions and oxidation level of the samples was carried out.
An outstanding introduction to the fundamentals of regression analysis-updated and expanded The methods of regression analysis are the most widely used statistical tools for discovering the relationships among variables. This classic text, with its emphasis on clear, thorough presentation of concepts and applications, offers a complete, easily accessible introduction to the fundamentals of regression analysis. Assuming only a basic knowledge of elementary statistics, Applied Regression Analysis, Third Edition focuses on the fitting and checking of both linear and nonlinear regression models, using small and large data sets, with pocket calculators or computers. This Third Edition features separate chapters on multicollinearity, generalized linear models, mixture ingredients, geometry of regression, robust regression, and resampling procedures. Extensive support materials include sets of carefully designed exercises with full or partial solutions and a series of true/false questions with answers. All data sets used in both the text and the exercises can be found on the companion disk at the back of the book. For analysts, researchers, and students in university, industrial, and government courses on regression, this text is an excellent introduction to the subject and an efficient means of learning how to use a valuable analytical tool. It will also prove an invaluable reference resource for applied scientists and statisticians.
Coinage of terms like nutraceuticals, functional, and pharma foods has diverted the attention of human beings to where they are seeking more natural cures. Though pharmaceutical drugs have been beneficial for human health and have cured various diseases but they also impart some side effects. Numerous plants have been tested for their therapeutic potential; Nigella sativa, commonly known as black cumin, is one of them. It possesses a nutritional dense profile as its fixed oil (lipid fraction), is rich in unsaturated fatty acids while essential oil contains thymoquinone and carvacrol as antioxidants. N. sativa seeds also contain proteins, alkaloids (nigellicines and nigelledine), and saponins (alpha-hederin) in substantial amounts. Recent pharmacological investigations suggested its potential role, especially for the amelioration of oxidative stress through free radical scavenging activity, the induction of apoptosis to cure various cancer lines, the reduction of blood glucose, and the prevention of complications from diabetes. It regulates hematological and serological aspects and can be effective in dyslipidemia and respiratory disorders. Moreover, its immunopotentiating and immunomodulating role brings balance in the immune system. Evidence is available supporting the utilization of Nigella sativa and its bioactive components in a daily diet for health improvement. This review is intended to focus on the composition of Nigella sativa and to elaborate its possible therapeutic roles as a functional food to prevent an array of maladies.
The mixture of conjugated diene hyperperoxide isomers obtained from autoxidation of methyl linoleate was separated by high performance liquid chromatography (HPLC). Four major isomers were obtained from adsorption chromatography and identified as the 9 and 13 positional isomers having the trans-trans and cis-trans configurations. The latter geometrical isomers have the trans double bond adjacent to the hydroperoxide group. The hydroxy compounds (methyl hydroxylinoleates) obtained from the hydroperoxides by NaBH4 reduction were similarly separated but with improved resolution. This is the first instance of the complete separation of these compounds and provides a rapid method for their analysis. Unlike adsorption chromatography, reversed-phase chromatography separates the mixtures only according to the geometrical isomerism of the double bonds and not according to the position of the hydroxy or hydroperoxide function.
New geometric isomers, methyl (9Z,11Z)-13-hydroperoxy-9,11-octadecadienoate and methyl (10Z,12Z)-9-hydroperoxy-10,12-octadecadienoate, were proved to be present in methyl linoleate hydroperoxide produced by autoxidation. They were identified from their UV, MS, and 1H-NMR spectra after conversion to the corresponding oxo derivatives: methyl (9Z,11Z)-13-oxo-9,11-octadecadienoate and methyl (10Z,12Z)-9-oxo-10,12-octadecadienoate. Their chromatographic behavior is described.
The essential oil of black cumin seeds, Nigella sativa L., was tested for a possible antioxidant activity. A rapid evaluation for antioxidants, using two TLC screening methods, showed that thymoquinone and the components carvacrol, t-anethole and 4-terpineol demonstrated respectable radical scavenging property. These four constituents and the essential oil possessed variable antioxidant activity when tested in the diphenylpicrylhydracyl assay for non-specific hydrogen atom or electron donating activity. They were also effective.OH radical scavenging agents in the assay for non-enzymatic lipid peroxidation in liposomes and the deoxyribose degradation assay. GC-MS analysis of the essential oil obtained from six different samples of Nigella sativa seeds and from a commercial fixed oil showed that the qualitative composition of the volatile compounds was almost identical. Differences were mainly restricted to the quantitative composition.
Based on the understanding of lipid peroxidation as a free radical chain reaction, over 50 yr ago the three primary products of linoleic acid autoxidation were predicted to be the 9-, 11-, and 13-hydroperoxides. The 9- and 13-hydroperoxides were found at the time, but formation of 11-hydroperoxylinoleate or any other bis-allylic fatty acid hydroperoxide has not been reported heretofore as a product of lipid peroxidation reactions. In vitamin E-controlled autoxidation of methyl linoleate, the 11-hydroperoxy derivative was identified as the next most prominent primary peroxidation product after the 9- and 13-hydroperoxides. It was present in approximately 5-10% of the abundance of the 9- or 13-hydroperoxide. The structures of 1l-hydroperoxylinoleate and its 11-hydroxy derivative were established by high-pressure liquid chromatography, ultraviolet spectroscopy, gas chromatography mass spectroscopy, and 1H nuclear magnetic resonance spectroscopy. The 11-hydroperoxide was not detectable in the absence of (alpha-tocopherol, indicating that efficient trapping of the 11-peroxyl radical as the hydroperoxide is critical to permitting its accumulation.
NMR data on lipid hydroperoxides is scarce. In this study, hydroperoxides were produced from methyl 9-cis,11-trans-octadecadienoate and from methyl 10-trans,12-cis-octadecadienoate by autoxidation in the presence of 20% of alpha-tocopherol. Ten different hydroperoxides were isolated from the autoxidation mixtures of the two conjugated linoleic acid (CLA) methyl esters by SPE and HPLC. The assignment of the 1H and 13C NMR spectra of these hydroperoxides was accomplished by 2D NMR experiments and by spectral simulations. Substitution of a hydroperoxyl group at the allylic position in CLA methyl esters induced a 53.93 ppm downfield shift on the hydroperoxyl-bearing carbon resonance. The effects on the olefinic alpha, beta, gamma, and delta carbon resonances were -3.45, +4.96, -1.22, and +4.42 ppm, respectively. Furthermore, the solvent effects of deuterochloroform, deuteroacetone, and deuterobenzene on the 13C resonances of the hydroperoxides suggest that deuterochloroform is the appropriate solvent for 13C NMR studies on mixtures of lipid hydroperoxides.
Analysis of lipid oxidation
- A Kamal-Eldin
- Pocorny
Kamal-Eldin A, Pocorny J (2005) Analysis of lipid oxidation. AOCS Press, Champaign
Germany e-mail: christina.skiera@cvuaka.bwl.de C. Skiera Á P
- C Skiera
C. Skiera (&) Á U. Holzgrabe Institute of Pharmacy and Food Chemistry, University of Wü, Am Hubland, Wü, Germany e-mail: christina.skiera@cvuaka.bwl.de C. Skiera Á P. Steliopoulos Á T. Kuballa Chemisches und Veterinä Karlsruhe, Weißenburger Str. 3, 76187 Karlsruhe, Germany B. Diehl Spectral Service, Emil-Hoffmann-Str. 33, 50996 Kö, Germany References 1. (2011) European Pharmacopoeia 7th edition. European depart-ment for the quality of medicines, Strasbourg http://www. pheur.eu
Application of proton nuclear magnetic resonance (1H NMR) spectroscopy for assessment of oxidative stability of fats and oils Natural antioxidants—chemistry, health effects, and applications
- F Shahidi
- Un Wanasundara