Oxidation Of Methyl Linoleate Research Articles

Superoxide dismutase inhibits lipid peroxidation in micelles

Superoxide dismutase (SOD) taken in minor concentrations (a few U/ml) displays a pronounced inhibiting effect on the chain oxidation of methyl linoleate and methyl linolenate (but not methyl oleate) induced by 2,2′-azobis(2-amidinopropan) dihydrochloride (AAPH) in micellar solutions of sodium dodecyl sulfate and Triton X-100 in phosphate buffer, pH 7.40, at 37.0°C. The inhibition is evidently caused by purging the system from O 2 −. The latter suggests the formation of O 2 − (HO 2 ) in the course of peroxidation, most likely, via β-decay of lipid peroxy radical (LO 2 ). Thermodynamic estimations verify a rather high probability of β-decay of LO 2 produced from polyunsaturated fatty acids by contrast to that produced from saturated and monoenic fatty acids. It is speculated that O 2 − (HO 2 ), being an amphiphilic, reactive and highly mobile species, participates in intermicellar (interliposomal) transfer of free valence during lipid peroxidation in microheterogeneous systems.

Antioxidant effect of capsaicin on lipid peroxidation in homogeneous solution, micelle dispersions and liposomal membranes

The antioxidant activity of capsaicin (CAP) was measured in the oxidation of methyl linoleate (ML) in homogeneous solution, of ML micelles in aqueous dispersions and also of soybean phosphatidylcholine liposomal membrane, and was compared to that of -tocopherol (-TOH) which is one of the most important antioxidants in vivo. The reactivity of CAP toward galvinoxyl (a model phenoxyl radical) in acetonitrile solution was found to be much smaller than that of -TOH, suggesting that the radical scavenging activity of CAP is much weaker than that of -TOH. In fact, in homogeneous acetonitrile solution where the antioxidant activity is determined primarily by the chemical activity of the antioxidant toward peroxyl radicals, CAP inhibited the oxidation of ML much less efficiently than -TOH and a clear induction period was not observed. The antioxidant activity of CAP was found to be about 60 times smaller than that of -TOH in homogeneous solution. However, in micelle oxidation, the difference in antioxidant activity of the two antioxidants was much smaller than in homogeneous solution. Furthermore, in the membrane, CAP inhibited the oxidation almost as effectively as -TOH. These results suggest that CAP can act as an antioxidant in the biomembrane.

Superoxide dismutase enhances chain-breaking antioxidant capability of hydroquinones

2-tert-butyl-(1), 2,6-dimethyl-(2), 2,5-dimethyl-(3), trimethyl-(4), and 2,3-dimethoxy-5-methyl-(5) substituted p-hydroquinones (QH2) were tested as a chainbreaking antioxidant during the oxidation of methyl linoleate (ML) in dodecyl sulfate micellar solution, pH 7.40, at 37°C. In the absence of superoxide dismutase (SOD), all the studied QH2 displayed very moderate if any antioxidant capability. When 5–25 U/ml SOD was added, QH2 showed a pronounced ability to inhibit ML oxidation. The stoichiometric factor of inhibition was found to be about one for all the tested QH2 in the presence of SOD. The reactivities of QH2 to the ML peroxy radical increase in the order QH25 < QH2 3 < QH21≈QH22 < QH24; reactivity of QH24 exceds that reported for the majority of phenolic antioxidants. The features of QH2 as an antioxidant in aqueous environment is likely associated with the reactivity of semiquinone (O·-) formed due to attack of the peroxy radical to QH2. O·- reacts readily with molecular oxygen with formation of superoxide (O·-2); in turn, O·-2 attacks both to QH2 and ML (likely, as HO·2) that results in fast depleting QH2 and chain propagation, respectively. The addition of SOD results in purging a reaction mixture from O·-2 and, as a corollary, in depressing undesirable reactions with the participation of O·-2. Under these conditions, QH2 displays the theoretically highest inhibitory activity which is determined solely by the reactivity of QH2 to the peroxy radical.

Isolation and antioxidant activity of galloyl flavonol glycosides from the seashore plant, Pemphis acidula.

Four kinds of galloyl flavonol glycosides were found in the leaf extract of Pemphis acidula, a plant growing on the subtropical seashore. Their chemical structures were elucidated to be quercetin or kaempferol 6"-O-galloyl-beta-D-glycosides by using spectroscopic and chemical analyses. One of the flavonols, kaempferol-3-O-(6-O-galloyl-beta-D-galactopyranoside), was newly isolated from natural sources and its structure was completely determined in this investigation. The antioxidant-related activities of the galloyl flavonoids were examined by the DPPH antiradical activity, inhibition of methyl linoleate oxidation, and inhibition of oxidative cell death. These results were compared with those of the corresponding non-galloylated flavonol glycosides and their aglycones. The galloyl flavonoids showed more efficient activity than that of the corresponding flavonol glycosides, but not more than that of the corresponding aglycones in the three assays applied.

Identification, quantitative determination, and antioxidative activities of chlorogenic acid isomers in prune (Prunus domestica L. ).

Neochlorogenic acid (3-CQA) and cryptochlorogenic acid (4-CQA), isolated from prune (Prunus domestica L.), were identified by NMR and MS analyses. In addition, the quantity of chlorogenic acid isomers in prune were measured by HPLC. These isomers, 3-CQA, 4-CQA, and chlorogenic acid (5-CQA), were contained in the ratio 78.7:18. 4:3.9, respectively. 4-CQA was identified and quantified in prune for the first time, and relatively high amounts of this isomer were characteristic. Antioxidative activities of the chlorogenic acid isomers, such as scavenging activity on superoxide anion radicals and inhibitory effect against oxidation of methyl linoleate, were also evaluated. Each isomer showed antioxidative activities which were almost the same.

Ability of surfactant hydrophobic tail group size to alter lipid oxidation in oil-in-water emulsions.

Oxidation of oil-in-water emulsion droplets is influenced by the properties of the interfacial membrane surrounding the lipid core. Previous work has shown that an important factor in the oxidation of oil-in-water emulsions is surfactant properties that impact interactions between water-soluble prooxidants and lipids in the emulsion droplet. The purpose of this research was to study the impact of surfactant hydrophobic tail group size on lipid oxidation in oil-in-water emulsions stabilized by polyoxyethylene 10 lauryl ether (Brij-lauryl) or polyoxyethylene 10 stearyl ether (Brij-stearyl). The ability of iron to decompose cumene peroxide was similar in hexadecane emulsions stabilized by Brij-stearyl and Brij-lauryl. Oxidation of methyl linoleate in hexadecane emulsions containing cumene peroxide was greater in droplets stabilized by Brij-lauryl than in those stabilized by Brij-stearyl at pH 3 with no differences observed at pH 7.0. Oxidation of salmon oil was greater in emulsions stabilized by Brij-lauryl than in those stabilized by Brij-stearyl as determined by both lipid peroxides and headspace propanal. These results suggest that surfactant hydrophobic tail group size may play a minor role in lipid oxidation in oil-in-water emulsions.

Isolation and structure determination of new antioxidative ferulic acid glucoside esters from the rhizome of Alpinia speciosa, a Zingiberaceae plant used in Okinawan food culture.

An assay-guided isolation gave three antioxidants including two newly identified compounds from the rhizomes of Alpinia speciosa, which is used as an important plant in the food culture of the Okinawa area of Japan. Spectroscopic analysis of the two new compounds revealed them to be new glucoside esters of ferulic acid. The antioxidant activity of the esters was measured using two different methods. Both compounds showed greater activity than that of Trolox in the TLC method; however, one of the compounds showed weaker inhibitory activity than that of Trolox and epicatechin against AMVN-induced methyl linoleate oxidation.

Antioxidant action of the antihypertensive drug, carvedilol, against lipid peroxidation

The action of carvedilol, a vasodilating, β-adrenoceptor blocking agent, against lipid peroxidation has been the subject of many studies, but the results reported thus far are contradictory. In an attempt to define the antioxidant mechanism of carvedilol against lipid peroxidation, the dynamics of the action of carvedilol were studied in several oxidation systems. We investigated the reactivity of carvedilol toward radicals and its inhibitory effect on lipid peroxidation induced by several kinds of initiating species such as azo compounds and metal ions in solution, micelles, membranes, and low-density lipoprotein. Carvedilol exerted poor reactivity toward phenoxyl, alkoxyl, and peroxyl radicals in acetonitrile solution nor did it show an appreciable antioxidant effect against either the peroxyl radical-induced oxidation of methyl linoleate in acetonitrile or against phosphatidylcholine liposomal membranes in aqueous suspension. Carvedilol completely inhibited the ferric ion-induced oxidation of methyl linoleate micelles by sequestering ferric ions, but not by reducing hydroperoxide. It was shown that carvedilol enhanced the oxidation of micelles induced by either methemoglobin or peroxyl radical. Carvedilol, which was added exogenously, did not suppress the oxidation of isolated low-density lipoprotein induced by peroxyl radical or cupric ion. These results show that carvedilol does not act as a radical-scavenging antioxidant, but that it does act most efficiently as an antioxidant against ferric ion-induced oxidation by sequestering ferric ion.

Effects of β-carotene and retinal on the formation of methyl linoleate hydroperoxides

In order to clarify the prooxidative role of carotenoids on the oxidation of unsaturated lipids this study examined the effects of β-carotene and its oxidative breakdown product, retinal, on primary oxidation products of linoleic acid methyl ester. Formation as well as isomer distribution of methyl linoleate hydroperoxides were followed by highperformance liquid chromatography. Oxidation of methyl linoleate without or with added β-carotene (5, 20, 200 μg/g) or retinal (7, 18, 180, 360 μg/g) was carried out in the dark under air at 40 °C. Both β-carotene and retinal promoted the formation of hydroperoxides and thus acted as prooxidants in a concentration-dependent way. Moreover, carotenoids also had an effect on the isomeric distribution of primary oxidation products as high contents of retinal increased the portion (%) of trans,trans-hydroperoxides. Being thermodynamically more stable isomers than cis,trans-isomers of hydroperoxides they are known to accumulate during later phases of oxidation or during hydroperoxide decomposition. The results showed that β-carotene and retinal were not effective hydrogen donors. These findings raise the question that carotenoids and their oxidative breakdown products enhance the decomposition of lipid hydroperoxides and this effect partially explains the prooxidative effect of carotenoids.

Effects of β-carotene and retinal on the formation of methyl linoleate hydroperoxides

In order to clarify the prooxidative role of carotenoids on the oxidation of unsaturated lipids this study examined the effects of β-carotene and its oxidative breakdown product, retinal, on primary oxidation products of linoleic acid methyl ester. Formation as well as isomer distribution of methyl linoleate hydroperoxides were followed by high-performance liquid chromatography. Oxidation of methyl linoleate without or with added β-carotene (5, 20, 200 μg/g) or retinal (7, 18, 180, 360 μg/g) was carried out in the dark under air at 40 °C. Both β-carotene and retinal promoted the formation of hydroperoxides and thus acted as prooxidants in a concentration-dependent way. Moreover, carotenoids also had an effect on the isomeric distribution of primary oxidation products as high contents of retinal increased the portion (%) of trans,trans-hydroperoxides. Being thermodynamically more stable isomers than cis,trans-isomers of hydroperoxides they are known to accumulate during later phases of oxidation or during hydroperoxide decomposition. The results showed that β-carotene and retinal were not effective hydrogen donors. These findings raise the question that carotenoids and their oxidative breakdown products enhance the decomposition of lipid hydroperoxides and this effect partially explains the prooxidative effect of carotenoids.

Degradation of Lycopene, α‐Carotene, and β‐Carotene During Lipid Peroxidation

ABSTRACT:The stability and antioxidant effectiveness of lycopene, a‐carotene, and b‐carotene were compared during oxidation of methyl linoleate at 37 and 60 °C. Two carotene concentrations, 80 or 160 mg/g of methyl linoleate, were used to determine a concentration effect. At 37 °C, the degradation rates were: lycopene &gt; β‐carotene &gt; α‐carotene. Lycopene and α‐carotene inhibited hydroperoxide formation, lycopene being the more effective antioxidant. β‐Carotene inhibited hydroperoxide formation at the lower concentration but did not show an antioxidant effect at the higher concentration. At 60 °C, the carotenes degraded 6 to 8 times faster than at 37 °C and did not show an antioxidant effect. BHT or α‐tocopherol effectively suppressed the hydroperoxide formation and degradation of the carotenes.

Action of pyrroloquinolinequinol as an antioxidant against lipid peroxidation in solution.

The activities of pyrroloquinoline quinone (PQQ), a coenzyme of methanol dehydrogenase and amine oxidase, and its reduced form pyrroloquinoline quinol (PQQH2) as an antioxidant have been measured in solution. PQQH2 was stable in the absence of oxygen but rapidly auto-oxidized to PQQ in the presence of oxygen in water. PQQH2 was stable in an aprotic solvent such as acetonitrile, even in air. PQQ did not exert appreciable antioxidant activity, whereas PQQH2 exerted higher reactivity than alpha-tocopherol toward galvinoxyl radical and peroxyl radical. PQQH2 acted as a potent antioxidant against the oxidation of methyl linoleate in acetonitrile induced by azo compound and produced a clear induction period, from which the apparent stoichiometric number was obtained as 1.1. PQQH2 reduced the alpha-tocopheroxyl radical and spared alpha-tocopherol in the oxidation of methyl linoleate. These results suggest that PQQH2 may act as a potent antioxidant, particularly in combination with alpha-tocopherol.

Comparative study on dynamics of antioxidative action of α-tocopheryl hydroquinone, ubiquinol, and α-tocopherol against lipid peroxidation

α-Tocopheryl quinone is a metabolite of α-tocopherol (TOH) in vivo. The antioxidant action of its reduced form, α-tocopheryl hydroquinone (TQH 2), has received much attention recently. In the present study, the antioxidative activity of TQH 2 was studied in various systems in vitro and compared with that of ubiquinol-10 (UQH 2) or TOH to obtain the basic information on the dynamics of the antioxidant action of TQH 2. First, their hydrogen-donating abilities were investigated in the reaction with galvinoxyl, a stable phenoxyl radical, and TQH 2 was found to possess greater second-order rate constant (1.0 × 10 4 M −1 s −1) than UQH 2 (6.0 × 10 3 M −1 s −1) and TOH (2.4 × 10 3 M −1 s −1) at 25°C in ethanol. The stoichiometric numbers were obtained as 1.9, 2.0, and 1.0 for TQH 2, UQH 2, and TOH, respectively, in reducing galvinoxyl. Second, their relative reactivities toward peroxyl radicals were assessed in competition with N,N′-diphenyl-p-phenylenediamine (DPPD) and found to be 6.0 (TQH 2), 1.9 (UQH 2), and 1.0 (TOH). Third, their antioxidant efficacies were evaluated in the oxidation of methyl linoleate in organic solvents and in aqueous dispersions. The antioxidant potency decreased in the order TOH > UQH 2 > TQH 2, as assessed by either the extent of the reduction in the rate of oxidation or the duration of inhibition period. The reverse order of their reactivities toward radicals and their antioxidant efficacies was interpreted by the rapid autoxidation of TQH 2 and UQH 2, carried out by hydroperoxyl radicals. Although neither TQH 2 nor UQH 2 acted as a potent antioxidant by itself, they acted as potent antioxidants in combination with TOH. TQH 2 and UQH 2 reduced α-tocopheroxyl radical to spare TOH, whereas TOH suppressed the autoxidation of TQH 2 and UQH 2. In the micelle oxidation, the antioxidant activities of TQH 2, UQH 2, and TOH were similar, whereas 2,2,5,7,8-pentamethyl-6-chromanol exerted much more potent efficacy than TQH 2, UQH 2, or TOH. These results clearly show that the antioxidant potencies against lipid peroxidation are determined not only by their chemical reactivities toward radicals, but also by the fate of an antioxidant-derived radical and the mobility of the antioxidant at the microenvironment.

Antioxidant Activity and Partitioning of Phenolic Acids in Bulk and Emulsified Methyl Linoleate

To evaluate the effect of colloidal parameters on the activity of natural antioxidants, the effect of selected phenolic acids on both bulk and emulsified methyl linoleate oxidation (in the dark at 40 degrees C) was examined. Oxidation was monitored by determining the formation of hydroperoxides; their isomer distribution and ketodiene (oxodiene) products were monitored by using high-performance liquid chromatography. This study showed the system- and concentration-dependent antioxidant activity of phenolic acids. The scavenging of alpha,alpha-diphenyl-beta-picrazylhydrazyl radicals reflected the antioxidant activity in a bulk oil system but not in an emulsion. Specific interactions of the antioxidant with other compounds, for example, the emulsifier, and intramolecular hydrogen bonds may play an important role in reducing the antioxidant activity. Furthermore, these interactions of antioxidants with emulsifier have a strong influence on the partitioning of antioxidants. Thus, the proportion of the antioxidant solubilized in the lipid phase and particularly in the interface did not necessarily reflect the efficiency of the antioxidant.

Proportion of geometrical hydroperoxide isomers generated by radical oxidation of methyl linoleate in homogeneous solution and in aqueous emulsion

The proportion of geometrical hydroperoxide isomers generated by aerobic oxidation of methyl linoleate (18:2 Me) in either aqueous emulsion consisting of Tris-HCl buffer (pH 7.4) or in a homogeneous dichloromethane solution was determined to understand the mechanism of lipid oxidation in different reaction systems. Four geometrical isomers were generated after oxidation of 18:2 Me in dichloromethane: methyl 13-hydroperoxy-cis-9, trans-11-octadecadienoate, methyl 13-hydroperoxy-trans-9,trans-11-octadecadienoate, methyl 9-hydroperoxy-trans-10,cis-12-octadecadienoate, and methyl 9-hydroperoxy-trans-10, trans-12-octadecadienoate in the ratios of 1:4:1:4, respectively. The ratios between each isomer did not change until the peroxide value (PV) increased to 58 meq/kg. Oxidation of 18:2 Me in aqueous emulsion yielded the same geometrical isomers of hydroperoxide. However, the ratios were different: 3:2:3:2 until the PV increased to 110 meq/kg. Predominant (60%) formation of trans,trans hydroperoxide isomers was obtained in the oxidation of a mixture of 18:2 Me and methyl laurate (12:0 Me). These results are interpreted to reflect the importance of the concentration of hydrogen atom-donating equivalents to the kinetic preference for different products. The high effective concentration of hydrogen donors in the oxidation of 18:2 Me in emulsions favored the formation of the less stable cis,trans isomers. The lower concentration of hydrogen donor in the dichloromethane solution effectively slowed hydrogen donation and led to the strong preference for the more stable trans,trans isomers. This interpretation was further tested by preparing emulsions of 18:2 Me and 12:0 Me to dilute concentration of hydrogen-donating species using the nonhydrogen-donating 12:0 Me. Consistent with the proposed hypothesis, the proportion of trans,trans isomers increased as a result of 12:0 Me addition.

Action of quinolinic and indolinonic aminoxyls as radical-scavenging antioxidants

The kinetic studies on the actions of quinolinic and indolinonic aminoxyls in the oxidation of lipid peroxidation induced by free radicals were carried out to evaluate their antioxidant activity. These aminoxyls showed a similar reactivity toward peroxyl radical with α-tocopherol. The antioxidant efficacies of aminoxyls against oxidation of methyl linoleate in homogeneous solution were smaller than that of α-tocopherol. Hydroxylamine, a reduced form of aminoxyl, possessed a comparative antioxidant efficacy with α-tocopherol and was capable of suppressing the consumption of α-tocopherol. Aminoxyls showed more potent antioxidant activity than α-tocopherol against the oxidation of methyl linoleate micelles induced by peroxyl radical or by a combination of copper ion and hydrogen peroxide. These results suggest that quinolinic and indolinonic aminoxyls may act as potent antioxidants against lipid peroxidation, especially in the presence of a good reductant which reduces aminoxyl radicals to hydroxylamines.

Anti- and Prooxidant Properties of Carotenoids

Carotenoids can be effective singlet oxygen quenchers and inhibit free-radical induced lipid peroxidation. A remarkable property of β-carotene (1a) is the change from an antioxidant to a prooxidant depending on oxygen pressure and concentration. In the present study a considerable number of carotenoids (1a, 2c, 2d, 2e, 3a, 4a, 5a, 6a, 7a, 8a, 8h, 8i, 8j, 9f, 10a, 11a, 12g) was investigated using two independent approaches: 1. Comparison of their effects on inhibition of the free-radical oxidation of methyl linoleate, and 2. The direct study of the effect of oxygen partial pressure upon their rates of oxidation. It is shown that some carotenoids (7a, 8a) are even more effective than the well-known compounds β-carotene (1a) and astaxanthin (5a) and are powerful antioxidants without any prooxidative property. Different carotenoids display different behaviour depending on chain length and end groups. The influence of these functional groups on the antioxidative reactivity is discussed.

Flavonoids quercetin, myricetin, kaemferol and (+)-catechin as antioxidants in methyl linoleate

The antioxidant effect of the flavonoids quercetin, myricetin, kaemferol, (+)-catechin and rutin on methyl linoleate oxidation was investigated. In addition, the synergistic effects of flavonoids and α-tocopherol were studied. Oxidation was monitored by conjugated diene measurement and by determining the formation of hydroperoxide isomers by HPLC. The antioxidant activity of flavonoids in non-polar methyl linoleate differ from that previously reported in water-containing systems, such as LDL and liposome systems. The activity of antioxidants (10–1000 μM) measured by hydroperoxide formation decreased in the order: myricetin>quercetin>α-tocopherol>(+)-catechin >kaemferol=rutin. The antioxidant activity of flavonoids increased as the number of phenolic hydroxyl groups increased. In addition to the number of hydroxyl groups, other structural features such as the 2,3 double bond in the C-ring and a glycoside moiety in the molecule had an effect on the antioxidant activity. Myricetin and rutin, especially had a synergistic effect with α-tocopherol. Myricetin, quercetin and rutin protected α-tocopherol from decomposition, myricetin being the most protective. The relative hydrogen-donating activity measured by the ratio of cis,trans- to trans,transhydroperoxide isomers formed during oxidation decreased in the order: α-tocopherol >myricetin>quercetin. Hydroperoxide isomeric distribution of the samples containing kaemferol or rutin did not differ from the control. Thus, although α-tocopherol was the most effective hydrogendonor, myricetin and quercetin were more effective antioxidants in inhibiting the hydroperoxide formation in methyl linoleate. © 1999 Society of Chemical Industry

Effect of pH and temperature on comparative nonenzymatic browning of proteins produced by oxidized lipids and carbohydrates.

Bovine serum albumin (BSA) was incubated for 24 h in the presence of 10 mM ribose (RI), methyl linoleate hydroperoxides, or the secondary products of methyl linoleate oxidation (SP), at five temperatures (25, 37, 50, 80, and 120 degrees C) and different pHs (4, 7, and 10), to study the influence of these variables in the browning, fluorescence, amino acid losses, and pyrrolization of the modified proteins. All treated proteins exhibited similar colors and fluorescence spectra, and the spectra of their Ehrlich adducts were also analogous. However, at 25-50 degrees C the proteins treated with oxidized lipids exhibited higher color changes, amino acid losses, and pyrrolization than the BSA treated with RI, and these effects were much higher in proteins treated with RI at 80-120 degrees C. The effect of pH was similar in proteins treated with RI or SP. These results suggested a similarity for browned proteins obtained from both carbohydrates and oxidized lipids. In addition, both reactions seem to be complementary, because melanoidin formation derived from oxidized lipids can be produced under conditions different from those carbohydrate/protein reactions.

Antioxidant activity of flavonol aglycones and their glycosides in methyl linoleate

AbstractThe antioxidant activities of the flavonol aglycones, quercetin and myricetin, and their selected glycosides were compared in bulk methyl linoleate oxidized at 40°C. Methyl linoleate hydroperoxide formation, hydroperoxide isomer distribution, and ketodiene formation were followed by using high‐performance liquid chromatography (HPLC) analysis. The aglycones, quercetin and myricetin, were consistently more active in bulk methyl linoleate than their glycosides and more active than α‐tocopherol at 500 and 1000 µM. At 50 µM, the order of activity was myricetin &gt; α‐tocopherol &gt; quercetin, and the order of activity of quercetin and its derivatives was quercetin &gt; quercitrin &gt; isoquercitrin &gt; rutin. Myricitrin was slightly less active than myricetin. The sugar moiety was shown to have a marked effect on the antioxidant activity of flavonols. The rhamnoside derivatives, quercitrin and myricitrin, both possessed activity close to that of their corresponding aglycones. The different activities of glycosides could be partly explained by different solubilities and by differences in oxidizability of glycosides containing a monosaccharide or disaccharide at the C3 position. The effect on hydroperoxide isomer distribution indicates that α‐tocopherol was a more effective hydrogen donor than flavonoids, although flavonoids were more effective in inhibiting oxidation of methyl linoleate.