Autoxidation Of Methyl Linoleate Research Articles

Effect of water activity on secondary products formation in autoxidizing methyl linoleate

The role of water activity on the formation of peroxides and carbonyl compounds during lipid oxidation is important to know because there could be either beneficial or detrimental effects of water activity on lipid oxidation in stored foods. Therefore, methyl linoleate was chosen as a model lipid and was autoxidized to 1% at water activity ranging from 0.02 to 0.79 at 37°C. Oxygen uptake was monitored manometrically. The peroxide and carbonyl contents were determined upon termination of the autoxidation studies. Methyl linoleate autoxidation was characterized by three phases: i) an initial induction period of no oxygen absorption; ii) a slow rate of oxygen absorption, up to 0.15% oxidation; and iii) a relatively faster rate of oxygen absorption beyond 0.15% up to 1% oxidation. Water activity had considerable influence during the first phase. There was no induction period at or below water activity 0.22. The induction period begins at water activity 0.32 and could be extended to a limit with increase in water activity. Once the induction period was passed water activity had no influence on the rate of oxidation. However, during the second and third phases water activity becomes important in the stabilization of peroxides/hydroperoxides and decides the course of secondary reactions that follow peroxide decomposition. Higher water activity values, particularly water activity 0.67, tended to stabilize peroxides. Water activity had considerable influence on the formation of secondary products of autoxidation as evidenced by the variation in the type and quantity of carbonyl compounds at different water activity values.

Antioxidant activity of oxidation products of α‐tocopherol and of its model compound 2,2,5,7,8‐pentamethyl‐6‐chromanol

AbstractA variety of oxidation products (4–29) of α‐tocopherol, 1 and of its model compound, 2,2,5,7,8‐pentamethyl‐6‐chromanol (2) has been tested for antioxidant activity against autoxidizing safflower oil (ASO) and autoxidizing methyl linoleate (AML). The following compounds showed good antioxidant activity against both substrates: 5‐hydroxymethyl‐2,2,7,8‐tetramethyl‐6‐chromanol (4), 5‐(2,2,5,7,8‐pentamethyl‐6‐chromanoxy)methyl‐2,2,7,8‐tetramethyl‐6‐chromanol (15), 1,2‐bis(2,2,7,8‐tetramethyl‐6‐chromanol‐5‐)ethane (16), 5‐ethoxymethyl‐7,8‐dimethyltocol (19), 5‐mthoxymethyl‐2,2,7,8‐tetramethyl‐6‐chromanol (21), 5‐ethoxymethyl‐2,2,7,8‐tetramethyl‐6‐chromanol (20), 5‐propoxymethyl‐2,2,7,8‐tetramethyl‐6‐chromanol (22), 5‐butoxymethyl‐2,2,7,8‐tetramethyl‐6‐chromanol (23), 5‐(2‐methyl‐1‐propoxy)methyl‐2,2,7,8‐tetramethyl‐6‐chromanol (24), 5‐(2‐methyl‐2‐propoxy)methyl‐2,2,7,8‐tetramethyl‐6‐chromanol (25), 5‐heptoxymethyl‐2,2,7,8‐tetramethyl‐6‐chromanol (26), 5‐undecoxymethyl‐2,2,7,8‐tetramethyl‐6‐chromanol (27), 5‐phytoxymethyl‐2,2,7,8‐tetramethyl‐6‐chromanol (28) and 5‐cholesteroxymethyl‐2,2,7,8‐tetramethyl‐6‐chromanol (29). 2,2,7,8‐Tetramethylchroman‐5,6‐dione (17) and 1,2‐bis(2,2,7‐trimethylchroman‐5,6‐dione‐8‐)ethane (18) showed significant antioxidant activity against ASO but not against AML. If the corresponding oxidation products of 1 are formedin vivo it means that the antioxidant activity of 1 is not lost on oxidation. This may help to explain the outstanding capacity of 1 to protect cell membranes.

Antioxidative mechanism of maize zein in powder model systems against methyl linoleate: effect of water activity and coexistence of antioxidants

Food proteins such as soybean protein, milk casein, maize gluten, and zein were examined against methyl linoleate autoxidation in powder model systems. A gas chromatography method was employed to estimate antioxidant activity by measuring oxygen consumption of head-space gas. Water activity affected the antioxidant efficacy when tocopherol was added to the proteins.

Oxidative Dimerization of Sesamol in Methyl Linoleate under A. O. M. Condition

A methyl linoleate solution of sesamol was oxidized by air under A. 0. M. A biphenyl type dimer of sesamol was detected in the reaction mixture, but no diphenyl ether type dimer.Changes in the concentrations of sesamol and its dimer during autoxidation were followed by HPLC. At an earlier stage of autoxidation, decrease in sesamol and increase in the dimer were noted, followed by subsequent decrease in the latter. Sesamol and its dimer could no longer be detected at the end of the induction period, as was also noted for BHA and its dimers during autoxidation of methyl linoleate as reported previously.

A study of the autoxidation of some unsaturated fatty acid methyl esters using Fourier transform Raman spectroscopy

Near-infrared Fourier transform Raman and Fourier transform infrared spectroscopy have been used to investigate the chemical changes taking place during the curing reaction of several fatty acid methyl esters, which are used for modelling processes in the autoxidation of alkyd resin coatings. We have studied methyl oleate, methyl linoleate, and methyl linolenate in an attempt to monitor the degree of unsaturation within the fatty acid methyl esters (FAMES) during the complex autoxidation/polymerisation reaction that takes place once the paint system is coated onto a substrate and exposed to the atmosphere. The peaks around 1655 cm −1 have been assigned as follows: to the trans isomer at 1670 cm −1, the cis isomer at 1655 cm −1 and the conjugated structure at 1640 cm −1 [B. Schrader, Raman/Infrared Atlas of Organic Compounds (2nd Edn), VCH, Weinheim (1989); J. K. Abenyega, M. Claybourn and G. Ellis, in preparations]. Raman spectra for the cure of methyl linoleate after 24 h show several interesting features, suggesting the formation of a highly conjugated cyclic structure. Current theories about the mechanism for the autoxidation of methyl linoleate make no mention of this aromatic product.

Oxidative Dimerization of t-Butylated Hydroxyanisole (BHA) during Autoxidation of Methyl Linoleate and the Influences of Phospholipids and Tri-n-octylamine on the Dimerization

The oxidative decomposition of t-butylated hydroxyanisole (BHA) and formation of its dimers were investigated during the autoxidation of methyl linoleate (ML). The effects of phospholipids (PL) and tri-n-octylamine (TOA) on oxidative dimerization were also examined.ML, in which BHA had been dissolved, was oxidized by air at 60°C in the dark. The specific surface area was 16.9 cm2/g. The extent of oxidation of ML was determined from weight increase resulting from oxygen uptake. The stability of ML toward autoxidation was estimated by the induction period before acceleration of oxygen uptake. After oxidation for a fixed time, an aliquot of the reaction mixture was subjected to HPLC analysis to determine the amount of the BHA monomer and its dimers.At an earlier stage of autoxidation, decrease in the amount of BHA monomer and increase in dimers were seen, followed by a decrease in the dimers, and the amounts of both the BHA monomer and its dimers were zero at the end of the induction period. Dimer quantities (ratio of the dimers to the initial BHA concentration) in the reaction mixture with a high initial concentration of BHA were larger than those with low initial concentration. A diphenyl ether type dimer was predominantly formed during autoxidation, and the amount of a diphenyl ether type dimer was about ten times that of a biphenyl type dimer.The oxidative dimerization of BHA during the autoxidation of ML containing phosphatidyl ethanolamine (PE) or phosphatidyl choline (PC) in various concentrations was followed so as to investigate synergism between BHA and PL. A remarkable increase in the stability of ML containing BHA was observed by the addition of PE at a low concentration. The efficiency of PC as a synergist was essentially the same as that of PE. The velocity of decomposition of BHA was lowered and the amounts of the dimers formed decreased by the addition of PL.Synergism between TOA and BHA was quite strong and the effect of TOA on the oxidative dimerization of BHA was unique. A large amount of a biphenyl type dimer, i. e. the amount corresponding to BHA monomer disappeared, was formed within the first 5 d of autoxidation, followed by a small change in the ratio of BHA monomer to its dimers.

The Oxidation Products from Two Kinds of Tocopherols Co-Existing in Autoxidation System of Methyl Linoleate

The oxidation products of both types of mixtures of alpha-tocopherol (alpha-Toc) and gamma-tocopherol (gamma-Toc) or alpha-Toc and delta-tocopherol (delta-Toc) during autoxidation of methyl linoleate were isolated and identified. The structures of the oxidation products were characterized by UV, IR, 1H and 13CNMR, and mass spectrometry. The 5-[2-(alpha-tocopherol-5'-yl)ethyl]-alpha-tocopherylquinone, 5-[2-(alpha-tocopherol-5'-yl)ethyl]-8a-hydroxy-alpha-tocopherone, O-[8-(5-ethoxymethyl-7-methyltocol)methyl]-alpha-tocopherol were obtained from both types of the mixtures as the oxidation products derived from alpha-Toc. gamma-Toc diphenyl ether dimer (gamma-TED) and gamma-Toc biphenyl dimer (gamma-TBD) were identified from the mixture of alpha-Toc and gamma-Toc, and delta-Toc diphenyl ether dimer (delta-TED) from the mixture of alpha-Toc and delta-Toc. However, no oxidation product composed of both alpha-Toc and gamma-Toc or delta-Toc was detected in oxidation products of both types of the mixtures. These results support the facts that, at first, oxidation of alpha-Toc proceeds during autoxidation of lipids and then gamma-Toc or delta-Toc decomposes after approximate consumption of alpha-Toc.

Simultaneous intake of tocopherol and autoxidized oils reduces the lymphocytic damage by dietary autoxidized oils.

This paper reports the effects of simultaneous intake of dl-α-tocopherol and autoxidized methyl linoleate (ML) on lymphocytic damage by dietary autoxidized ML

Free radical scavenging and cytotoxic properties in the ellipticine series

In the series of cytotoxic intercalating compounds derived from ellipticine, we tried to correlate free radical scavenging properties with cytotoxic activities. Scavenging properties were determined in vitro on two experimental models: a) antioxidant activity of the drugs during the autoxidation of methyl linolenate induced by azo-bis-isobutyronitrile; this activity was measured either by the initial rate ratios in the presence and in the absence of the drug or by the length of the inhibition period of the reaction in the presence of the drug and b) ability to reduce DPPH free radicals. Cytotoxic properties were expressed by ID50 the dose which reduces by 50% the L 1210 cell growth rate as compared to controls after 48 h. It appears that antioxidant activity and reduction of DPPH both require the presence of a free OH group on the ellipticine ring. A good correlation is observed between cytotoxicity and antioxidant activity of the hydroxylated derivatives; minor structural modifications which result in a loss of cytotoxic activity also result in a loss of antioxidant properties. No such correlation is observed with DPPH reducing properties of ellipticine derivatives.

Rapid headspace gas chromatography of hexanal as a measure of lipid peroxidation in biological samples.

A rapid, sensitive and convenient capillary gas chromatographic-headspace method was developed to determine hexanal as an important volatile decomposition product of hydroperoxides formed from n-6 polyunsaturated fatty acids in rat liver samples. Total volatiles were also determined as a measure of overall lipid peroxidation. Samples of headspace taken from sealed serum bottles incubated at 37 degrees C were injected into a gas chromatograph. It was possible to make 15 determinations per hour. This method is convenient because no special sample manipulations are necessary. The addition of 0.5 mM ascorbic acid prior to gas chromatographic analysis significantly increased hexanal production. The applicability of the method was demonstrated in studies of the effect of iron in the presence or absence of hydroperoxides of methyl linoleate and methyl linolenate and tert-butyl hydroperoxide on rat liver homogenates, slices and microsomes. A rapid silica cartridge chromatographic procedure was used to purify hydroperoxides from autoxidized methyl linoleate and methyl linolenate, and hydroperoxy epidioxides (cyclic peroxides) from autoxidized methyl linolenate in 20-40 mg quantities. The hydroperoxides and hydroperoxy epidioxides of methyl linolenate were effective inducers of n-6 polyunsaturated fatty acid peroxidation in liver homogenates. Hexanal and thiobarbituric acid-reacting substances were significantly correlated in liver homogenates and microsomes but not in slices. This specific method for hexanal, a known product of peroxidation of n-6 polyunsaturated fatty acids, can be used as a good measure of lipid peroxidation.

Autoxidation of methyl linoleate initiated by the ozonide of allylbenzene.

Allylbenzene ozonide (ABO), a model for polyunsaturated fatty acid (PUFA) ozonides, initiates the autoxidation of methyl linoleate (18:2 ME) at 37 degrees C under 760 torr of oxygen. This process is inhibited by d-alpha-tocopherol (alpha-T) and 2,6-di-tert-butyl-4-methylphenol (BHT). The autoxidation was followed by the appearance of conjugated diene (CD), as well as by oxygen-uptake. The rates of autoxidation are proportional to the square root of ABO concentration, implying that the usual free radical autoxidation rate law is obeyed. Activation parameters for the thermal decomposition of ABO were determined under N2 in the presence of radical scavengers and found to be Ea = 28.2 +/- 0.3 kcal mol-1 and log A = 13.6 +/- 0.2; kd (37 degrees C) is calculated to be (5.1 +/- 0.3) X 10(-7) sec-1. Autoxidation data are also reported for ozonides of 18:2 ME and methyl oleate (18:1 ME).

The effect of dietary autoxidized oils on immunocompetent cells in mice

Effects of dietary autoxidized oil on immunocompetent cells, such as splenocytes and thymocytes, were studied in mice. When the autoxidized methyl linoleate was administered orally to male C57BL/6 mice in a single dose, the DNA synthesis of thymocytes was remarkably depressed 1 day after the treatment, and then the mitogenic response to concanavalin A of splenocytes was increased 3 days after the dose. With long-term (90 days) feeding of slightly autoxidized soybean oil (with a peroxide value of 150 mequiv/kg) in mice, the DNA synthesis of thymocytes was depressed and the mitogenic response to concavanalin A of splenocytes was increased. No effect was observed on plasma glutamic acid-oxaloacetic acid transminase and glutamic acid-pyruvic acid transaminase levels, nor on liver thiobarbituric acid reactants due to the dose of autoxidized soybean oil. These findings indicate that oral intake of autoxidized oil effects immunocompetent cells and causes depression of the DNA synthesis of thymocytes in mice.

Oxidation of Lipids. XVI. Inhibition of Autoxidation of Methyl Linoleate by Diarylamines

Abstract The inhibition of oxidation of methyl linoleate in homogeneous solution and in aqueous dispersions by diarylamines has been studied. Diphenylamines with electron-donating substituents exhibited antioxidant activities, while those having electron-withdrawing substituents such as niflumic acid and flufenamic acid did not suppress the oxidation appreciably. When both 4,4′-dimethoxydiphenylamine and α-tocopherol were present as antioxidants, only α-tocopherol was consumed at first and when α-tocopherol was almost completely depleted, 4,4′-dimethoxydiphenylamine began to be consumed to give nitroxide radical, which further acted as antioxidant.

Formation of fluorescent substances from degradation products of methyl linoleate hydroperoxides with amino compound.

The degradation products formed from methyl linoleate hydroperoxides by reaction with heme were fractionated by Sephadex LH-20 column chromatography and by reverse-phase high performance liquid chromatography, and the ability of each compound to form fluorescent substances through reaction with amino compound was compared. Maximum formation of fluorescent substances was obtained from monomeric degradation products with amino compound, but low molecular weight aldehydes such as hexanal, 2-hexenal and 2,4-decadienal, formed only a small amount of fluorescent substances. However, the major monomeric degradation products described previously, the hydroxy-, keto- and epoxy-derivatives, do not significantly contribute to the formation of fluorescent substances through reaction with amino compound. It was suggested that formation of fluorescent substances from lipid peroxides with amino compound may originate from a precursor present in monomeric degradation products formed from hydroperoxide of methyl linoleate during lipid peroxidation, and that low molecular weight aliphatic aldehydes are not involved in fluorescent substance formation. Moreover, the majority of TBA-reactive substances in secondary oxidation products prepared from autoxidized methyl linoleate are also unrelated to the formation of fluorescent substances through reaction with amino compound.

Identification of the most intense odor compounds formed during autoxidation of methyl linolenate at room temperature

AbstractThe volatile compounds formed during autoxidation of methyl linolenate (MLe) at 22–24°C were analyzed by a technique which reveals the flavor compounds having the highest flavor units (ratio of the concentration to the odor treshold). After a reaction time of 48 hr, when ca. 20 mol percent of the MLe had been converted into hydroperoxides,trans, cis‐2,6‐nonadienal followed by 1,cis‐5‐octadien‐3‐one,rans,cis‐3‐5‐octadien‐2‐one andcis‐3‐hexenal showed the highest flavor units. After 102 hr 1,cis‐5‐octadien‐3‐one was by far the most important odor compound, followed bycis‐3‐hexenal andtrans,cis‐2,6‐nonadienal.

Formation of trimers of alpha-tocopherol and its model compound, 2,2,5,7,8-pentamethylchroman-6-ol, in autoxidizing methyl linoleate.

The reaction products of alpha-tocopherol and its model compound, 2,2,5,7,8-pentamethylchroman-6-ol, during the autoxidation of methyl linoleate at 37 C were investigated. Two isomeric trimers were obtained as the major reaction products of alpha-tocopherol, and a trimer was obtained as that of its model chroman. The structure of each trimer has been characterized by IR, UV, 1H and 13C NMR, and mass spectroscopy. The 13C NMR spectra showed the presence of a quaternary carbon atom and a carbon atom bearing two oxy substituents in the molecule. On methanolysis of each trimer, equimolar amounts of the 5-methoxymethyl compound and the dihydroxy dimer were formed, indicating the presence of a ketal group in the molecule. From these results, new trimeric structures are proposed. The reaction products of alpha-tocopherol could be well-separated by reverse-phase high performance liquid chromatography. When methyl linoleate was autoxidized in the presence of 1 mol% alpha-tocopherol, spirodiene dimer was the initial reaction product of alpha-tocopherol, and trimers were formed with the decrease of alpha-tocopherol.

Autoxidative dimerization of methyl linolenate and its monohydroperoxides, hydroperoxy epidioxides and dihydroperoxides

AbstractThe structures of dimers and oligomers produced by autoxidation of methyl linolenate and its purified oxidation products were investigated to obtain a better understanding of the mechanism of oxidative deterioration of unsaturated lipids. The dimers were separated by gel permeation chromatography, characterized by molecular weight determinations before and after sodium borohydride reduction, and analyzed by ultraviolet, infrared,1H NMR and fast atom bombardment mass spectrometry. Autoxidation of methyl linolenate at 40 C to peroxide value of 1062 produced 6.8% dimers mainly derived from hydroperoxides, hydroperoxy epidioxides and dihydroperoxides. These dimers were 88% peroxide‐linked (C‐O‐O‐C) and 12% ether‐ (C‐O‐C) and/or carbon‐linked (C‐C). Autoxidation of methyl linolenate monohydroperoxides at 40 C produced dimers that were 72% peroxide‐ and 28% ether/carbon‐linked. Thermal decomposition of linolenate hydroperoxides at 150 C gave dimers that were 100% ether/carbon‐linked, and catalytic decomposition with ferric chloride‐ascorbic acid at room temperature gave dimers with 43% peroxide and 57% ether/carbon linkages. Autoxidation of linolenate hydroperoxy epidioxides at 40 C produced dimers containing hydroperoxy epidioxides, dihydroperoxides and monohydroperoxides joined with peroxide and ether/carbon linkages. Under the same conditions, autoxidation of linolenate dihydroperoxides produced dimers containing dihydroperoxides and hydroperoxy epidioxides joined with peroxide and ether/carbon linkages. These dimers contribute to oxidative and flavor deterioration of polyunsaturated fats in the same way as the hydroperoxide precursors by further decomposition to produce volatile compounds.

Oxidative Dimerization of Tocopherols during the Course of Autoxidation of Methyl Esters of Saturated and Unsaturated Fatty Acids. III.

Theeffects of phospholipids on the oxidative decompositionand dimerization of d-γ-tocopherol (γ-T) or d-δ-tocopherol (δ-T) during the autoxidation of methyl linoleate (Me-Li) or methyl laurate (Me-La) were investigated. The fatty acid methyl esters, which contained tocopherol (0.5 %) and one of following additives (0.01-0.5 %) were oxidized by air under A.O.M. conditions. The additives used in the experiments are as follows : phosphatidylcholine (PC) and phosphatidylethanolamine (PE) as phospholipids, tri-n-butylphosphate (TBP) as a model component of phosphate ester, and tri-n-octylamine (TOA) as that of a nitrogenous base. The amounts of tocopherol and its dimers formed in a reaction mixture were determined by HPLC. PC and PE improved the stability of the tocopherol monomer in Me-Li (Figs.-1 and 7) and suppressed the formation of its dimers (Figs.-2, 3, 8 and 9). The total amount of the tocopherol monomer and its dimers was constant regardless of the presence of phospholipids (Figs.-4 and 10). It is thus evident that phospholipids suppress the initial stage of the oxidation of tocopherol, in which tocopherol changes to its dimers, and that they also contribute to the regeneration of the tocopherol monomer from its dimers. TBP, by which the stability of tocopherol under the condition of the thermal oxidation was improved, promoted the oxidation of tocopherol (Figs.-1 and 7) and suppressed the dimerization of tocopherol (Figs.-2, 3, 8 and 9) under the autoxidative conditions of Me-Li. The oxidation of tocopherol in Me-Li was promoted by TOA at low concentration (0.01 %). The oxidative decomposition of tocopherol decreased with the concentration of TOA. However, TOA eventually suppressed the oxidation of tocopherol (Figs.-1 and 7) and formed mainly diphenylether type dimed (Figs.-2 and 8).

Effect of metal salts and fructose on the autoxidation of methyl linoleate in emulsions.

Effet des sels metalliques suivants: CdCl 2 , CoCl 2 , Cr(NO 3 ] 3 , CuSO 4 , FeSO 4 , FeCl 3 , HgCl 2 , MnSO 4 et ZnSO 4

Studies on inhibition mechanism of autoxidation by tannins and flavonoids. III. Inhibition mechanism of tannins isolated from medicinal plants and related compounds on autoxidation of methyl linoleate

Studies on inhibition mechanism of autoxidation by tannins and flavonoids. III. Inhibition mechanism of tannins isolated from medicinal plants and related compounds on autoxidation of methyl linoleate