Autoxidation Of Methyl Linoleate Research Articles

The mechanism of synergism between tocopherols and trimethylamine oxide in the inhibition of the autoxidation of methyl linoleate.

The synergistic effect of trimethylamine oxide (TMAO) on the antioxidant activity of γ-tocopherol (γ-Toc) to inhibit the autoxidation of methyl linoleate was investigated.Formation of the reducing dimers of γ-Toc was found to be closely related to the synergism of TMAO with γ-Toc. γ-Toc diphenyl ether dimer and two γ-Toc biphenyl dimers were identified, and the latters were considered to be atropisomers with each other.From the reaction of the hydroperoxide (LOOH) of methyl linoleate with TMAO, TMAO was found to act as a peroxide decomposer. TMAO produced methyl keto-octadecadienoate, which was formed only in the presence of γ-Toc and TMAO, from LOOH, and markedly decreased the POV of LOOH.A possible mechanism of synergism between Toc and TMAO in the inhibition of the autoxidation of methyl linoleate was proposed.

Studies on the Toxicity of the Autoxidized Oils. VII.

In a previous paper, the acute toxicity of methyl linoleate hydroperoxides (LMHPOs) and secondary oxidation products on mice were reported histopathologically. In that paper, the authors noticed that LMHPOs and secondary oxidation products showed similar toxic effects, i.e. gross symptoms were observed in small intestine, liver, lung and kidney. Marked symptoms which were observed in tissues were necrosis, fatty accumulation, and congestive hyperemia. The present study was designed to clarify histopathologically the mechanism of chronic toxicity induced by autoxidized oils. Two kinds of autoxidized methyl linoleate were used for experiments, one contained hydroperoxides (AOML-1) and the other was secondary oxidation products rich (AOML-2).Those autoxidized methyl linoleates were administered to mice orally in one-tenth or one-twentyth of the amounts of acute toxicity for 2 months. The mice were inspected during the feeding period. The died and/or survived mice were anatomized and small intestine, liver, lung, and kidney were separated immediately from body. The chronic toxicity occurred only when sample oils were administered over a definite amount (one-tenth of the amount of acute toxicity) to mice. The chronic toxicity was similar to acute toxicity in the symptoms. However, such symptoms were more severe than that of acute toxicity. From the fact that feeding of small amounts of sample oils had no detectable toxic effects, whereas they were toxic when sample oils were ingested in larger amounts, we noticed the existence of a barrier for the occurrance of chronic toxicity. From the results obtained, we conclude that the mechanism of chronic toxicity caused by autoxidized oils is almost similar to that of acute toxicity.

Geometrical Isomers of Monohydroperoxides Formed by Autoxidation of Methyl Linoleate

Geometrical Isomers of Monohydroperoxides Formed by Autoxidation of Methyl Linoleate

Analysis of fat deterioration‐comparison of some photometric tests

Abstract and SummaryEight photometric methods (e.g., measurement of the diene absorption, ferrous isothiocyanate test, thiobarbituric acid value test, anisidine value, Kries test) for analysis of the oxidative deterioration of fats were compared with respect to sensitivity against autoxidized methyl linoleate and methyl linolenate. The ferrous isothiocyanate test was found to be the most sensitive method followed by the measurement of diene absorption. For assessment of the specificity, highly autoxidized methyl linoleate was separated by column chromatography into the following classes of compounds: volatile carbonyl compounds, monohydroperoxides, and polar peroxides‐1 and‐2. The influence of each class of compounds on the results of the eight tests was determined.

Autoxidation of methyl linolenate: Analysis of methyl hydroxylinolenate isomers by high performance liquid chromatography.

The mixture of methyl hydroxylinolenates obtained by reduction of the hydroperoxide isomers formed by autoxidation of methyl linolenate was resolved by high performance liquid chromatography into eight major components. These are positional isomers with the hydroxyl group at positions 9, 12, 13, and 16. Two geometrical isomers of each positional isomer are present; these differ in the configuration of the conjugated double bonds (cis-trans andtrans-trans). Autoxidation of methyl linolenate is regioselective and favors the formation of positional isomers 9 and 16.

Prooxidant effects of inorganic chromium compounds in the autoxidation of methyl linoleate

Abstract and SummaryThe prooxidant property of inorganic chromium compounds was determined in methyl linoleate free from natural antioxidants and metals. Prooxidant properties of inorganic chromium compounds appeared in order of sodium chromate > chromium (VI)‐oxide > chromium chloride > potassium chromate > chromium (III)‐oxide > potassium dichomate. In comparison with the control, additions of chromium compounds induced different amounts of autoxidation products derived from methyl linoleate, such as small amounts of hydroperoxides and conjugated dienes and large amounts of hydroxy groups,α,β,γ,δ‐unsaturated carbonyls, isolatedtrans double bonds, polymers, and free radicals. From these analytical data, the catalysis of chromium compounds in the autoxidation of methyl linoleate seemed to be based on their abilities of abstracting a hydrogen from methyl linoleate and decomposing hydroperoxides derived from the autoxidation of methyl linoleate.

Quantitative Analyses of Tocopherols in Autoxidized Methyl Linoleate

An attempt to quantitate the tocopherol content in the autoxidized methyl linoleate was made by the iron (III) chloride-2, 2'-bipyridine method. But the quantitation was very difficult owing to the interference of hydroperoxides. This interference was also observed in t-butyl and cumene hydroperoxides, but not in di-t-butyl and dicumene peroxides. Such hydroperoxides as autoxidized methyl linoleate, t-butyl and cumene hydroperoxides catalyzed the Emmerie-Engel color reaction by itself as if it contained tocopherols. This result is contradictory to the earlier studies that the peroxides in fats inhibited the color development in the Emmerie-Engel procedure. Tocopherols in autoxidized methyl linoleate were quantitatively determined when hydroperoxides were removed by the potassium iodide treatment.

Autoxidation of methyl linoleate. Separation and analysis of isomeric mixtures of methyl linoleate hydroperoxides and methyl hydroxylinoleates.

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.

Geometrical isomers of monohydroperoxides formed by autoxidation of methyl linoleate.

Isomeric monohydroperoxides produced from autoxidized methyl linoleate were separated into two geometrical isomers (cis-trans and trans-trans) by silver nitrate TLC. Purified monohydroperoxides were converted into hydroxy octadecadienoates. Trimethylsilyl (TMS) derivatives of these compounds (four components) were separated into three peaks in the gas chromatogram; the mixture of 9-hydroxy-cis, trans-isomer and 13-hydroxy-cis, trans-isomer, 9-hydroxy-trans, trans-isomer and 13-hydroxy-trans, trans-isomer. The trans-trans isomers became more dominant than the cis-trans isomers in the later stage of autoxidation and with the rise of temperature. At the degradation of monohydroperoxides, the decrease of trans-trans isomers was apparently slower than that of cis-trans isomers. It is proposed that cis, trans isomerization of monohydroperoxides takes place at the process of autoxidation of methyl linoleate.

Tocopherols as Antioxidants in Autoxidation of Methyl Linoleate. I.

The antioxidant activities of dl-α-tocopherol (α-T), d-γ-tocopherol (γ-T), and d-δ-tocopherol (δ-T) were determined in methyl linoleate free from natural antioxidants and metals. The relative antioxidant activities of tocopherols, at the equivalent mole concentration, were in the order α- γ->δ-T. The rate of the formation of tocopheroxyl radicals was in the order α->γ->δ-T. In the experiments oxidizing tocopherols by PbO2, etc., the mobility of hydroxyl hydrogen of tocopherols and the stability of tocopheroxyl radicals were in the order α-> γ->δ-T. These data showed that the ability as hydrogen donors was in the order α->γ->δ-T. However, tocopherols were consumed by direct air oxidation in the order α-> γ->δ-T. These results suggest that superior hydrogen donors are not always excellent antioxidants. Because, the substituent effect of antioxidants, as shown in tocopherols, can increase not only the ability of antioxidant as hydrogen donor but also the unstability of antioxidant against air.

Lipid degradation products capable of reacting with amino acid - Identification of 4-hydroxy-2-hexenal, 9-formyl methyl-8-nonenoate, and 10-formyl methyl-9-decenoate from autoxidized methyl linolenate.

Gel chromatography of autoxidized methyl linolenate on Bio-Beads S-X3 gave a degradation product fraction which was discolored by shaking with 0.5M Gly at 45°C for 90 min. IR spectra obtained before and after the discoloration reaction, showed that the absorptions at 5.96 μ due to C=O of conjugated carbonyl, 6.13 μ due to conjugated C=C and 10.3 μ due to trans C=C were remarkably reduced by the discoloration reaction. After conversion of carbonyl group into dimethylhydrazone and of hydroxyl group into TMS ether, the degradation products were analyzed by GLC and GC-MS. Some of conjugated carbonyls that decreased after the discoloration reaction were identified as 4-hydroxy-2-hexenal, 9-formyl methyl-8-nonenoate and 10-formyl methyl-9-decenoate.

A Long-Term Nutritional Study with Autoxidized Oil

In the previous paper, authors reported that triglyceride content in the liver of rat given orally autoxidized methyl linoleate increased 18 h after the administration of the oxidized ester, but during these periods, no change was observed in the activities of the enzymes such as α-glycerophosphate dehydrogenase and triglyceride synthetase related with lipid synthesis in the liver. One of the purposes of this experiment is to examine whether the same phenomenon observed in the previous experiment occures among the mice fed on autoxidized safflower oil for long time. Commercial stock diet, 10g per mouse are fed as basal diet to one of the three groups each consisting of 50 mice. Mice in other two groups recieved 0.1 ml of fresh or autoxidized safflower oil per mouse by mixing each with 10g of the basal diet, respectively. Feedings were continued for 9 months and observnation was performed on growth rate and mortality during this period. Five mice of each group were killed at 2, 9, 14, 30 and 39 weeks after the start of feeding to determine blood glucose level, hepatic triglyceride and cholesterol contents and activities of various enzymes in liver. The following results were obtained : 1. The autoxidized oil obviously caused the lowerimg of average gain of the body weights of mice of the group fed this oil as compared with other two groups fed on basal diet or with fresh oil. 2. At the time when the lowering of body weight gain was observed, the mortalities of the mice of this group became higher than those of other two groups. 3. The glucose levels in bloods, triglyceride and cholesterol contents to livers did not show any difference among three test groups fed on basal diet, with fresh oil and with oxidized oil. 4. In the present experimetal conditions, no clear difference in tested enzyme activities in livers of mice was observed among the three test groups mentioned above.

Ion exchange resins and ethyleneimine polymer as antioxidants: I. Activity and mechanism

AbstractThe antioxidant activity of ion exchange resins and ethyleneimine polymer was determined in methyl linoleate free from natural antioxidants and metals. Superior antioxidant activities were recognized in an ion exchange resin with NH groups and in the ethyleneimine polymer. The antioxidant activities in these heterogeneous reaction systems increased in linear proportion to the amount present. These antioxidant activities in the heterogeneous reaction system were mainly owing to their ability to donate hydrogen to the peroxy radicals produced in the autoxidation of methyl linoleate. The antioxidant radicals produced in these cases were very stable and generally couldn't participate in the increase of the induction periods in the autoxidation of methyl linoleate by terminating the peroxy radicals. These results have never been obtained in the homogeneous reaction system but are characteristic in the heterogeneous one.

Phenothiazine derivatives as new antioxidants for the autoxidation of methyl linoleate and their reaction mechanisms

AbstractThe effect of new antioxidants, such as phenothiazine derivatives, on the autoxidation of methyl linoleate was evaluated by estimating the induction period using the weighing method. Peroxide values (iodometry and IR), refractive indices, mol wts, and UV and IR spectra were measured to investigate the extent of the autoxidation. The induction period evaluated from the weighing method gives almost the same value as that from the peroxide values. It was shown that some new phenothiazine derivatives are remarkably effective antioxidants, and, besides, the mechanism for the autoxidation of methyl linoleate containing phenothiazine derivatives as antioxidants is probably of the same type as that for the substrate alone. This study also investigated the reaction mechanism of phenothiazine derivative antioxidants by determining the electron spin resonance spectra for the antioxidants in the autoxidation of methyl linoleate. Then, the following mechanism was proposed. That is, within the induction period, these inhibitors hold stable nitroxide radicals (>NO*) in the reaction between the antioxidant amino radical (>N*), produced by the reaction of the antioxidant with ROO* or O2, and the peroxy radical (ROO*). Besides, the more superior the phenothiazine derivative antioxidant, the more inactive the antioxidant makes oxygen and the peroxy radical for the methyl linoleate autoxidation and also for the antioxidant oxidation.

Metal‐requiring and non‐metal ‐ requiring catalysts in the autoxidation of methyl linoleate

AbstractDuring the autoxidation of methyl linoleate, peroxide‐containing substances are formed which, when added to unoxidized methyl linoleate, will catalyze oxygen uptake. Materials active only in the presence of added metal ions (MCs) were not inactivated during aerobic thin‐layer chromatography on silicic acid or alumina but were selectively inactivated by treatment with triphenylphosphine. Catalysts not requiring added metal ions for activity (NCs) are not affected by triphenylphosphine, but the catalytic activity is lost during aerobic thin‐layer chromatography. Autoxidized methyl linoleate was separated into four peroxide‐containing fractions by elution from a silicic acid column with hexane‐diethyl ether mixtures. Each fraction was found to contain both MCs and NCs.

Studies on the role of vitamin E in the oxidation of blood components by fatty hydroperoxides

Studies are reported on the oxidation of vitamin E and changes in lipid and fatty acid composition of rat blood components incubated in vitro with hydroperoxides prepared from autoxidized methyl linoleate. Red blood cells, plasma, serum, and hemoglobin free stroma were incubated at 37 °C with suspensions of linoleate hydroperoxide in Tris buffer at pH 7.4. The RBC were destroyed and substances with excitation-fluorescent properties were produced. Phosphatidylethanolamine, vitamin E and unsaturated fatty acids were oxidized in the reaction. Among the reaction products were substances that gave a positive thiobarbituric acid value, tocoquinone, and an unidentified substance isolated in the nonsaponifiable fraction of the lipid extract of the hemolyzed red cells. The reaction of linoleate hydroperoxide with stroma was similar to that with red blood cells and the same products were observed. In contrast there was little reaction of linoleate hydroperoxide with vitamin E or lipids of the serum or plasma in the absence of red blood cells. The destruction of the red blood cells appeared to be closely related to the oxidation of vitamin E indicating that the strong antioxygenic action of vitamin E in vivo was due to its particular form or structural orientation in the red cell membrane.

Further oxygenated compounds produced from methyl linoleate monohydroperoxides at the process of autoxidation.

The primary stable products, methyl linoleate monohydroperoxides (MLHPO), formed by the autoxidation of methyl linoleate were characterized by gas chromatography-mass spectrometry. MLHPO was converted into methyl hydroxy stearates which consisted of two isomers, methyl 9-hydroxy and methyl 13-hydroxy stearate. Trimethylsilyl ether derivatives of these hydroxy isomers were separated directly by gas chromatography and mass fragmentgraphy. MLHPO was degradated by incubating under aerobic condition at 37°C for a week, and the quantity of MLHPO was determined as hydroxy derivatives. Decrease of MLHPO was almost similar to that of conjugated diene structure, but the peroxide value was not appreciably decreased during the incubation. This fact based on the formation of further oxygenated compounds. After chemical reduction, these compounds were identified as methyl 9,13-hydroxy octadecenoate and methyl 9,12,13- or 9,10,13-trihydroxy octadecenoate, in which oxygen attached to the conjugated diene. The formation m...

Degradation process of autoxidized methyl linoleate.

Methyl linoleate (ML) and methyl linoleate hydroperoxides (MLHPO) were degradated by incubating under an aerobic condition at 37°C for a week. Identification of secondary degradation products (SP) by gas chromatography-mass spectrometry showed that the high proportions of hexanal, methyl octanoate and 8-formyl methyl octanoate (8-FMO) were found in degradated ML or MLHPO. In degradation of MLHPO, the decrease of peroxide value (POV) was slower than that of conjugated diene. In the earlier stage, POV was scarcely decreased, but in the later stage, MLHPO disappeared and another secondary hydroperoxides were produced. ML decreased linearly during 4-day incubation and the amount reached to 10% of the original one. The formation of 8-FMO was delayed to the increase of POV. Degradation process of autoxidized ML was discussed with the changes of POV, UV absorption and the amount of 8-FMO, and a formation mechanism of some SP was proposed.

リノレン酸メチル自動酸化生成物のゲルクロマト法による分画とその変色力

Components of autoxidized methyl linolenate were fractionated on a Bio-Beads S-X3 column with benzene as the eluting solvent. The elution sequence was in the order of decreasing molecular weight: tetramer ?? trimer, dimer and monomer containing degradation products. This was confirmed by comparing their elution behaviors with those of authentic compounds, and by molecular weight analysis. Discoloration potentialities of the eluted fractions were investigated by the treatment with nitrogenous compounds. In the case of the reaction with VBN prepared from Jack mackerel (Trachurus japonicus), or ammonia, only lipophilic discolored substances were produced, whereas in the case with non-VBN or amino acids, lipophilic and hydrophilic discolored substances were produced. Appapent differences in the discoloration potentiality-curves of lipophilic and hydrophilic discolored substances and the presence of degradation products which formed hydrophilic discolored substances by the reaction with non-VBN or amino acids but not with VBN or ammonia indicated that each discolored substance was produced by a different mechanism.

Study on quantitative analyses of hydroperoxides and alcohols by NMR shift reagent

AbstractRecently, much literature concerning the effects of NMR shift reagents upon compounds with Lewis's basic functional groups have been reported. These literatures have shown the effects of NMR shift reagents upon hydroxyl, amino, carbonyl, ether, ester carbonyl, cyano, and epoxy compounds but not hydroperoxyl compounds. Chemical and paramagnetic shifts of protons in t‐butyl and cumene hydroperoxides, t‐butyl and 2‐phenyl‐2‐propyl alcohols, and autoxidized methyl linoleate with incremental additions of an NMR shift reagent were determined. These experimental results indicated that each alcohol and hydroperoxide could be determined separately and quantitatively even in their mixtures. Moreover, this method can be recommended to obtain information about the structures of hydroperoxides, as well as alcohols.