Autoxidation Of Methyl Linoleate Research Articles

Oat avenanthramides exhibit antioxidant activities in vitro

Avenanthramides are a group of alkaloids that consist of an anthranilic acid derivative linked to a hydroxycinnamic acid derivative by a pseudo peptide bond, which are constituents of oat ( Avena sativa L.) grain. The three most abundant avenanthramides, N-(4′-hydroxy-3′-methoxycinnamoyl)-5-hydroxyanthranilic acid (Bf), N-(4′-hydroxycinnamoyl)-5-hydroxyanthranilic acid (Bp), and N-(3′,4′-dihydroxycinnamoyl)-5-hydroxyanthranilic acid (Bc), were synthesized and purified. These were tested for antioxidant activity using two in vitro systems: inhibition of β-carotene bleaching and reaction with the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH). Each avenanthramide displayed antioxidant activity in both systems. Bc had greater activity than Bp and Bf. Bc was nearly as active as the standard synthetic antioxidant, butylated hydroxytoluene (BHT) in the β-carotene system. In the DPPH system, Bc and Bf were more active than 6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox®). The relative activities of the avenanthramides corresponded to those determined for their component hydroxycinnamic acid moieties using an aqueous DPPH system or in a lipophilic system that measured the autoxidation of methyl linoleate.

Ascorbic acid and ascorbyl palmitate have only minor effect on the formation and decomposition of methyl linoleate hydroperoxides

Effects of ascorbic acid (AA) and ascorbyl palmitate (AP) on lipid hydroperoxides were evaluated during the formation and decomposition of methyl linoleate hydroperoxides (ML-OOH). AA and AP at 1 and 10 mM levels had no effect on the formation of ML-OOH during the autoxidation of methyl linoleate at 40 °C. However, depending on the reaction medium, AA and AP at 0.2 and 2 mM either slightly inhibited or accelerated the decomposition of 40 mM cis, trans ML-OOH in hexadecane or in hexadecane-inwater emulsion. The increased decomposition rate of ML-OOH, when compared to a control sample, was apparently due to the reductive activity of AA and AP on metal ions present in the system, as the addition of EDTA improved the stability of ML-OOH. The more detailed analysis of the decomposition reactions of ML-OOH suggests that under favorable reaction conditions AA and AP were, to some extent, capable of acting as hydrogen atom donors to peroxyl radicals and reducers of hydroperoxides to more stable hydroxy compounds. However, since all these effects of AA and AP on lipid hydroperoxides were relatively small, it is assumed that the antioxidative activity of AA and AP as well as their effect on the stability and reactions of lipid hydroperoxides in biological systems and in foods is mainly related to their synergistic interactions with other antioxidative compounds such as tocopherols.

Ascorbic acid and ascorbyl palmitate have only minor effect on the formation and decomposition of methyl linoleate hydroperoxides

Effects of ascorbic acid (AA) and ascorbyl palmitate (AP) on lipid hydroperoxides were evaluated during the formation and decomposition of methyl linoleate hydroperoxides (ML-OOH). AA and AP at 1 and 10 mM levels had no effect on the formation of ML-OOH during the autoxidation of methyl linoleate at 40 °C. However, depending on the reaction medium, AA and AP at 0.2 and 2 mM either slightly inhibited or accelerated the decomposition of 40 mM cis, trans ML-OOH in hexadecane or in hexadecane-inwater emulsion. The increased decomposition rate of ML-OOH, when compared to a control sample, was apparently due to the reductive activity of AA and AP on metal ions present in the system, as the addition of EDTA improved the stability of ML-OOH. The more detailed analysis of the decomposition reactions of ML-OOH suggests that under favorable reaction conditions AA and AP were, to some extent, capable of acting as hydrogen atom donors to peroxyl radicals and reducers of hydroperoxides to more stable hydroxy compounds. However, since all these effects of AA and AP on lipid hydroperoxides were relatively small, it is assumed that the antioxidative activity of AA and AP as well as their effect on the stability and reactions of lipid hydroperoxides in biological systems and in foods is mainly related to their synergistic interactions with other antioxidative compounds such as tocopherols.

Hydroperoxide formation during autoxidation of conjugated linoleic acid methyl ester

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 α-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 α-tocopherol and that the major isomers of CLA methyl ester hydroperoxides have a conjugated monohydroperoxydiene structure similar to that in linoleate hydroperoxides.

Antioxidant mechanism of flavonoids. Solvent effect on rate constant for chain-breaking reaction of quercetin and epicatechin in autoxidation of methyl linoleate.

The rate of oxygen depletion, as measured by electron spin resonance spectroscopy (oximetry using a spin probe), in a homogeneous solution of peroxidating methyl linoleate (initiated by an azo initiator) in the presence or absence of antioxidants was converted to second-order rate constants for the inhibiting reaction of quercetin and epicatechin. In the non-hydrogen-bonding solvent chlorobenzene at 50 degrees C, k(inh) had values of 4.3 x 10(5) M(-)(1) s(-)(1) for quercetin and 4.2 x 10(5) M(-)(1) s(-)(1) for epicatechin, respectively. In the hydrogen-accepting "water-like" solvent tert-butyl alcohol, the values were 2.1 x 10(4) and 1.7 x 10(4) M(-)(1) s(-)(1), respectively. The solvent effect (factor of 20) is more significant than for alpha-tocopherol (factor of 4), and the two flavonoids have efficiencies comparable to that of alpha-tocopherol in scavenging peroxyl radicals in the nonpolar solvent but not in the hydrogen-bonding solvent.

Autoxidation of methyl linoleate: identification of the bis-allylic 11-hydroperoxide.

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.

Antioxidant reactions of alpha-tocopherolhydroquinone.

Alpha-tocopherolhydroquinone (TQH2) is a product of alpha-tocopherol oxidation/reduction that exerts antioxidant effects in biological systems. TQH2 inhibited autoxidation of methyl linoleate initiated by peroxyl radicals derived from thermolysis of 2,2'-azobis(2,4-dimethylvaleronitrile) in acetonitrile. TQH2 oxidation yielded alpha-tocopherolquinone (TQ) as a major product and 2,3-epoxy-alpha-tocopherolquinone and 5,6-epoxy-alpha-tocopherolquinone as minor products. Each TQH2 consumed approximately two peroxyl radicals in the course of the oxidation. The data suggest that TQH2 scavenges peroxyl radicals primarily by electron transfer to form TQ and secondarily by addition-elimination to form the epoxyquinones.

Effects of α‐ and γ‐tocopherols on formation of hydroperoxides and two decomposition products from methyl linoleate

AbstractThe antioxidant effects of α‐and γ‐tocopherols (at 0, 10, 100, 500, and 1000 ppm) were evaluated in a model system based on the autoxidation of methyl linoleate in bulk for 4 d at 40°C. Samples were collected every 24 h and analyzed for the 9 cis,trans, 9 trans,trans, 13 cis,trans, and 13 trans,trans isomers of hydroperoxide, hydroxy, and ketodiene oxidation products by high‐performance liquid chromatography. Results showed that both α‐ and γ‐tocopherols are effective hydrogen donors as evidenced by their abilities to inhibit the formation of hydroperoxides, hydroxy compounds, and ketodienes and the cis,trans to trans,trans isomerization of hydroperoxides. Compared with γ‐tocopherol, α‐tocopherol was a more efficient antioxidant at very low concentrations (10 ppm) but a less efficient antioxidant at the high concentrations (100–1000 ppm). This paradoxical behavior is explained on the basis of differences in ease of hydrogen donation between the two tocopherol homologs. Although α‐tocopherol shows some loss of efficiency with increasing concentration, it is not a prooxidant when compared to the control void of antioxidants.

Antioxidant activity of plant extracts containing phenolic compounds.

The antioxidative activity of a total of 92 phenolic extracts from edible and nonedible plant materials (berries, fruits, vegetables, herbs, cereals, tree materials, plant sprouts, and seeds) was examined by autoxidation of methyl linoleate. The content of total phenolics in the extracts was determined spectrometrically according to the Folin-Ciocalteu procedure and calculated as gallic acid equivalents (GAE). Among edible plant materials, remarkable high antioxidant activity and high total phenolic content (GAE > 20 mg/g) were found in berries, especially aronia and crowberry. Apple extracts (two varieties) showed also strong antioxidant activity even though the total phenolic contents were low (GAE < 12.1 mg/g). Among nonedible plant materials, high activities were found in tree materials, especially in willow bark, spruce needles, pine bark and cork, and birch phloem, and in some medicinal plants including heather, bog-rosemary, willow herb, and meadowsweet. In addition, potato peel and beetroot peel extracts showed strong antioxidant effects. To utilize these significant sources of natural antioxidants, further characterization of the phenolic composition is needed.

Coexpression of Trypsin Inhibitory and Acceleratory Substances during Autoxidation of Methyl Linolenate

During the autoxidation of methyl linolenate, a group of degradation products capable of inhibiting β-trypsin activity were generated along with the accelerating substances, as also noted in a previous study. Chemical modification of the functional groups indicated the carbonyl and hydroxyl groups of the inhibitory degradation products and e-amino group (s) of trypsin to possibly be essential for the inhibition, but hydroperoxide not necessarily involved in inhibitory activity. The inhibitory degradation products inhibited α-chymotrypsin and lysozyme activity and thus may be inhibitors of various enzymes. There is thus the possibility that enzyme inhibitors and accelerators are generated spontaneously during the autoxidation of unsaturated lipids.

Bioluminescent Bacterial Genotoxicity Test for Fatty Acid Derivatives and Heated Oils

The Mutatox test (the commercial name for a bioluminescent bacterial genotoxicity test), which has been proved to be a good alternative to the Ames test, was used in this study to test the genotoxicity of fatty acid derivatives and heated oils. This test allows either pure or complex compounds to be rapidly screened for genotoxicity. Five different column fractions isolated from autoxidized methyl linoleate or autoxidized methyl linolenate were not genotoxic with or without the activation by the S-9 (microsomal) fraction. Chlorinated fatty acids including chloroethyl caprate, laurate, palmitate, and linoleate were genotoxic in the presence of S-9 activation. When heated at 180 °C, after 32 h, soybean oil exhibited genotoxic activity with or without the S-9 activation. The addition of 1% cholesterol into the soybean oil increased the onset of the genotoxicity during heating. Keywords: Mutatox test; genotoxicity test; fatty acid hydroperoxides; chlorinated fatty acids

Antioxidative activity and phenolic composition of pilot‐plant and commercial extracts of sage and rosemary

AbstractEight sage (Salvia officinalis) and twenty‐four rosemary (Rosmarinus officinalis) extracts, originating from pilot‐plant or commercial sources, had different antioxidative activities as measured by accelerated autoxidation of methyl linoleate. Twenty‐seven compounds were characterized in the Labiatae family extracts by high‐performance liquid chromatography (HPLC) coupled with mass spectrometry, equipped with an atmospheric pressure chemical ionization interface, and by HPLC coupled with a photodiode array spectrophotometer. Twenty‐two compounds were identified, including phenolic acids, carnosol derivatives, and flavonoids. The extracts showed great variation in their HPLC profiles, and no correlation was apparent between their antioxidative efficiency and their composition, in twenty specific phenols. Data indicated that the most effective compounds were carnosol, rosmarinic acid, and carnosic acid, followed by caffeic acid, rosmanol, rosmadial, genkwanin, and cirsimaritin.

Inhibition of Sardine Flesh Lipoxygenase by a New Antioxidant from Aspergillus terreus.

A new antioxidant and potent lipoxygenase (LOX) inhibitor, NC3B, was isolated from the fungus Aspergillus terreus and identified as 1, 3-dihydro-7-methyl-4, 5, 6-trihydroxy-isobenzofuran. Under weight gain method conditions with methyl linoleate as a substrate, NC3B was a stronger antioxidant than tocopherol (Toc) and acted as a weak Toc synergist during the autoxidation of methyl linoleate. NC3B significantly inhibited the oxidation of linoleic acid by sardine flesh LOX and caused reduction in oxygen uptake by the substrate.

Free-Radical Scavenging Reactions of .alpha.-Tocopherol during the Autoxidation of Methyl Linoleate in Bulk Phase

Methyl linoleate containing alpha-tocopherol was autoxidized at 37 and 60 degrees C in bulk phase. The reaction products of alpha-tocopherol at 37 degrees C were 4a,5-epoxy-8a-hydroperoxy-alpha-tocopherones (1), a mixture of methyl 9-(8a-dioxy-alpha-tocopherone)-10(E),12(Z)-octadecadienoates and methyl 13-(8a-dioxy-alpha-tocopherone)-9(Z),11(E)-octadecadienoates (2), a mixture of methyl 9-(alpha-tocopheroxy)-10(E),12(Z) -octadecadienoates and methyl 13-(alpha-tocopheroxy)-9(Z),11(E)-octadecadienoates (3), alpha-tocopherol spirodiene dimer (4), and alpha-tocopherol trimer (5). Compound 3 was the major product at 60 degrees C, and the E,E-isomers of 3 were produced in addition to the E,Z-isomers. When methyl linoleate containing a low concentration of alpha-tocopherol was autoxidized at 37 degrees C, alpha-tocopherol suppressed the formation of methyl linoleate hydroperoxides, and the main products of alpha-tocopherol were 1 and 2. In contrast, (alpha-tocopherol at a high concentration induced the accumulation of methyl linoleate hydroperoxides, and the reaction products were 1-5. The autoxidation at 60 degrees C proceeded rapidly, and the main product of alpha-tocopherol was 1. In addition, the accumulation of 3 was observed under air-insufficient conditions. The results indicate that the alpha-tocopheroxyl radical produced can react with both alkyl and alkylperoxyl radicals of unsaturated lipids during the autoxidation. Competing with these trapping reactions, 1 appears to be formed primarily by autoxidation reactions of alpha-tocopherol.

UV-initiated autoxidation of methyl linoleate in micelles studied by optical absorption

The UV-induced dissociation of lipid hydroperoxides, naturally present in methyl linoleate and methyl linoelaidate, was monitored by absorption spectroscopy. The decay of hydroperoxides in homogeneous solution, for a fluence rate of 0.82 mW·cm −2 at 240 nm, followed an exponential course with an average rate constant of k = (2.0 ± 0.1) · 10 −3 s −1. Addition of α-tocopherol led to an increase in the magnitude of k until it reached a limiting value of (3.4 ± 0.2) · 10 −3 s −1. When methyl linoleate (containing adventitous traces of hydroperoxides) was incorporated in SDS micelles, sustained UV irradiation caused initially an increase in the amounts of lipid hydroperoxides, due to linoleate autoxidation, followed by an exponential decrease due to photodissociation. From the initial rate of hydroperoxide formation (due to linoleate autoxidation) and the rate constant of the subsequent hydroperoxide decay, an oxidizibility of 0.61 · 10 −2 (Ms) −1/2 of methyl linoleate in micelles was deduced. It is suggested that UV irradiation and optical absorption afford an easy and reliable means for studying autoxidation of polyunsaturated fatty acids.

Inhibition of the Autoxidation of Methyl Linoleate by Protein and Highly Concentrated Dextrin in an Emulsion System

The autoxidation of methyl linoleate was studied in emulsions prepared with a mixture of protein and highly concentrated saccharide by a gel emulsification method. As the concentration of dextrin increased, the autoxidation became progressively slower, and at the concentration of 60%, it was strongly suppressed. The effects of proteins and an emulsifier on the retardation of autoxidation decreased in the following order: sodium caseinate > egg albumin > Tween-60 > BSA. Dextrin increased the stability to autoxidation when compared with mono- and di-saccharides. The stability to autoxidation was increased with decreasing dextrose equivalent (DE) of dextrin. From these results, the autoxidation of methyl linoleate in the emulsion prepared with sodium caseinate and 60% dextrin (DE 8 or 11) by the gel emulsification method was strongly inhibited.

Toxicological Study of Carbonyl Compounds Derived from Oxidized Lipids on Primary Cultured Rat Hepatocytes.

Toxicological studies of carbonyl compounds derived from oxidized lipids on primary cultured rat hepatocytes were investigated. As carbonyl compounds, saturated aldehyde, α, β-unsaturated aldehyde, glyoxals and malondialdehyde were used. Hepatocytes isolated from male Wistar rats by the collagenase perfusion method were cultured in 35 mm dishes in an atmosphere of 5% CO2-95% air at 37°C. Rat hepatocytes in culture for 24 h were incubated in Williams'E medium containing carbonyl compounds. Hepatotoxicity was estimated as the leakage of hepatic enzymes such as lactate dehydrogenase (LDH) and glutamic-oxalacetic transaminase (GOT) from the cells to medium. LDH and GOT activities were determined by an automatical analyzer. The order of hepatotoxic potency was as follows : glyoxals>α, β-unsaturated aldehydes>saturated aldehydes. Malondialdehyde had not hepatotoxicity. Hepatotoxicity of α, β-unsaturated aldehyde was inhibited by the addition of ascorbic acid and glutathione, whereas that of autoxidized methyl linoleate (peroxide value=2538 meq/kg and carbonyl value=872 mmol/kg) was inhibited by the addition of not only 3-tert-butyl-4-hydroxyanisole (BHA) and N, N'-diphenyl-p-phenylenediamine such as antioxidant, but also ascorbic acid and glutathione. From the above results, it is suggested that both hydroperoxides and α, β-unsaturated aldehydes contribute to the hepatotoxicity of autoxidized methyl linoleates.

Antioxidative components, xanthone derivatives, inSwertia japonica Makino

AbstractSubstances with antioxidative properties were obtained from an ether extract ofSwertia japonica Makino. Six active components of the extract were isolated and identified as methylbellidifolin, methylswertianin, swertianin, bellidifolin, norswertianin and desmethylbellidifolin. These six xanthone derivatives were shown to possess different antioxidant activities by chemiluminescent assay. The antioxidative activities of bellidifolin, norswertianin and desmethylbellidifolin were higher than those of butylated hydroxytoluene (BHT) and α‐tocopherol. On autoxidation of methyl linoleate, bellidifolin had activity similar to that of BHT. On the basis of the data present on antioxidative properties and data reported on the mutagenicities of the xanthones, both activities were shown to give a good correlation.

Lipid Peroxide Degradation by Intestinal Bacteria

Lipid peroxide degradation by intestinal bacteria was investigated. Methyl linoleate hydroperoxide (MLHPO) with a peroxide value of 1000 mEq/kg, which was prepared by autoxidation of methyl linoleate, was added to modified M10 medium at a concentration of 2000 p.p.m. After inoculation of a test bacterium, incubation was carried out with shaking at 37°C for 4 days in an anaerobic atmosphere. The residual MLHPO was measured by the thiobarbituric acid (TBA) reaction. Of the 140 strains (52 species) tested, 25 strains (13 species) were capable of reducing TBA values which ranged from zero to 67 per cent. Keywords - Lipid peroxide degradation; Intestinal bacteria; Linoleate hydroperoxide.

Effect of thioanisole and trimethylene sulfide on the oxidation and yellowing of methyl linolenate

The effect of thioanisole and trimethylene sulfide on the autoxidation and yellowing of methyl linolenate has been investigated by nuclear magnetic resonance (NMR) and ultraviolet visible spectroscopy, respectively. The progress of autoxidation was followed by measuring the NMR integration of vinylic protons with respect to methoxy protons, which served as the internal standard, as a function of time. The degree of yellowing was determined by measuring the difference in absorbance at 400 nm and 450 nm as a function of time. Both thioanisole and trimethylene sulfide enhanced the autoxidation of methyl linolenate. Inhibition of yellowing was observed only with trimethylene sulfide.