Tocopherol Oxidation Research Articles

Oil polyunsaturated fatty acid composition but not tocopherol levels determine oxylipin formation in plant and algae oils during pan-frying

The oxidation of linoleic acid (LA) and α-linolenic acid (ALA) in plant oils results in primary oxidation products known as oxylipins. It is not known whether the mechanisms of oxidation are driven primarily by oil polyunsaturated fatty acid (PUFA) composition (i.e., more double bonds resulting in more rapid oxidation) or antioxidant (tocopherol) content. The present study addressed this unknown by measuring the effects of pan-frying on LA- and ALA-derived oxylipin concentrations in plant and algae oils with different baseline fatty acid and tocopherol concentrations. Oxylipins, free fatty acids and tocopherols were quantified in algae, olive, corn, canola, and soybean oils before and after 30 minutes of pan-frying. Fatty acid epoxides and hydroxides of LA or ALA were significantly elevated after pan-frying, whereas fatty acid diols were reduced. The level of change in oxylipins was lower in low-PUFA algae and extra virgin olive oils compared to soybean, canola and corn oils (high in PUFAs). Tocopherols decreased significantly after 30 minutes of pan-frying, particularly in oils with low PUFA composition. Minor changes were observed in free fatty acids. Our findings demonstrate that oil PUFA composition is a greater determinant of lipid oxidation than tocopherol content, and that PUFAs in high LA or ALA oils may spare tocopherol oxidation by acting as free radical scavengers.

Lipoxygenase LOX3 Is the Enigmatic Tocopherol Oxidase in Runner Bean (Phaseolus coccineus).

Purification of extracts from the etiolated seedlings of runner bean (Phaseolus coccineus), coupled with mass spectrometry analysis of proteins revealed that the enzyme responsible for tocopherol oxidation activity is lipoxygenase, an enzyme known for enzymatic lipid peroxidation of unsaturated lipids. Biochemical analysis of the activity, along with the expression profile of three LOX isoforms (LOX1, LOX2, LOX3) in various parts of the etiolated seedlings, revealed that LOX3 was the major isoform expressed in the epicotyls, indicating that this isoform was responsible for the tocopherol oxidation activity; in the primary leaves, besides LOX3, the other two isoforms might have also contributed to the activity. The experiments performed in the model systems showed that unsaturated lipids were not required for the tocopherol oxidase activity, but that lipids were necessary to provide an optimal, hydrophobic environment of the substrate for the reaction. The experiments on lipoxygenase and tocopherol oxidase activities in the leaves of light-grown P. coccineus plants during aging and during storage of the extracts from etiolated seedlings showed that the activity of the first reaction decreased considerably faster than the latter, indicating different mechanisms of both reactions performed by the same enzyme. As LOX3 was shown to occur in the apoplast of the related species P. vulgaris, the question as to the physiological function of LOX3 in the tocopherol oxidation activity in P. coccineus is discussed.

Comparison of wheat germ and oil characteristics and stability by different stabilization techniques

In this study, the effects of four stabilization techniques (vibrated fluidized bed, oven, microwave, and extrusion) on the characteristics and stability of wheat germ and its oil were evaluated. The results showed that all methods were highly effective in inactivating lipoxygenase activity, although significant differences were observed in their ability to inactivate lipase activity. Among the techniques, extrusion was found to be the most effective, reducing residual lipase and lipoxygenase activity to less than 5% of that of fresh wheat germ. Acid value remained stable in the stabilized samples after 6 weeks of storage at 37 °C. However, the extrusion, oven, and microwave-treated samples showed rapid oxidation and/or significant losses of tocopherols (84.9%, 99.6%, and 33.9%, respectively). In contrast, wheat germ treated with the vibrated fluidized bed technique exhibited the best lipid stability, attributed to the suitable aw and few structural changes. Consequently, vibrated fluidized bed technique is recommended as the most suitable method for stabilizing wheat germ and producing high-quality wheat germ oil.

Impact of low oxygen storage on post-storage quality of pasteurized walnut (Juglans regia L.) kernels

Walnut (Juglans regia) kernels were obtained from two facilities, each using a different method for pasteurization to achieve a log 4 and log 5 reduction in the bacterial load on the kernel surface. Continuous pasteurization utilized high temperature steam applied for a short period, and batch pasteurization utilized lower temperature steam applied in a pressurized chamber for a longer period. Log 4 and 5 walnut kernels from both treatment methods were stored at 20 °C in air or sealed in bags with a low oxygen transmission rate, and an oxygen absorbing sachet was inserted to reduce internal oxygen concentrations to < 0.5 %. After pasteurization and packaging, walnuts were stored and evaluated periodically for peroxide value, hexanal, free-fatty acids, and total tocopherols. These objective quality measures were compared to descriptive sensory analyses of walnut taste, texture, and aroma conducted by a trained sensory panel. Continuous pasteurization of walnuts increased the rate of oil oxidation and loss of total tocopherols, but storage of walnuts in low oxygen atmospheres mitigated some of the negative quality impacts. Continuous pasteurization resulted in an immediate decreased in total tocopherols prior to storage under low oxygen atmospheres; however, low oxygen storage reduced subsequent losses in tocopherols. Batch pasteurization did not enhance quality degradation as compared to unpasteurized controls, but storage under low oxygen reduced oil oxidation and slowed the degradation of total tocopherols, as typically observed during walnut storage.

α-Tocopherol/Gallic Acid Cooperation in the Protection of Galactolipids Against Ozone-Induced Oxidation.

The protective ability of α-tocopherol (TOH) and gallic acid (GA) acting simultaneously at the moment of oxidizer application was evaluated by determination of galactolipid layers’ oxidation degree. Addition of GA resulted in a significant decrease of ozone-derived radicals shifting the threshold of lipid sensitivity by an amount approximately corresponding to the GA intake in bulk reaction with ozone. TOH presence in lipid layers results in a change of the role of GA which additionally may be involved in the reduction of tocopheroxyl radical formed during oxidation. This leads to a decrease in effectiveness of GA in diminishing the amount of ozone radicals. Such an effect was not observed for mixed layers containing galactolipid and pre-oxidized tocopherol where the ozone threshold level was associated with a stoichiometry of GA + O3 reaction. It was concluded that probably subsequent transformations of tocopheroxyl radical to less reactive forms prevent its reaction with GA the entire quantity of which is used for radicals scavenging. This result shows the role of time parameter in systems where substrates are engaged in various reactions taking place simultaneously. The inactivation of 1,1-diphenyl-2-picrylhydrazyl radical by studied antioxidants in homogeneous system confirmed observations made on the basis of lipid layer properties indicating their antagonistic action (at least at studied conditions). Formation of layers in post-oxidation situation did not depend whether tocopherol was oxidized during oxidation of lipid/tocopherol mixture or was introduced as pre-oxidized. This may be interpreted as indication that products of tocopherol oxidation may stabilize lipid layers.

Oxidative stability of a heme iron-fortified bakery product: Effectiveness of ascorbyl palmitate and co-spray-drying of heme iron with calcium caseinate

Fortification of food products with iron is a common strategy to prevent or overcome iron deficiency. However, any form of iron is a pro-oxidant and its addition will cause off-flavours and reduce a product’s shelf life. A highly bioavailable heme iron ingredient was selected to fortify a chocolate cream used to fill sandwich-type cookies. Two different strategies were assessed for avoiding the heme iron catalytic effect on lipid oxidation: ascorbyl palmitate addition and co-spray-drying of heme iron with calcium caseinate. Oxidation development and sensory acceptability were monitored in the cookies over one-year of storage at room temperature in the dark. The addition of ascorbyl palmitate provided protection against oxidation and loss of tocopherols and tocotrienols during the preparation of cookies. In general, ascorbyl palmitate, either alone or in combination with the co-spray-dried heme iron, prevented primary oxidation and hexanal formation during storage. The combination of both strategies resulted in cookies that were acceptable from a sensory point of view after 1year of storage.

Synthesis and analysis of tocopheryl quinone and tocopherol esters with fatty acids in heated sunflower oil

This work focuses on degradation of α‐tocopherol and formation of α‐tocopherol degradation products in sunflower oil heated at frying temperature. We determined the content and measured the kinetics of α‐tocopherol, α‐tocopheryl quinone, α‐tocopheryl fatty acid formation in heated sunflower oil without aeration (So) and in aerated oil (air flow 20 L/h) (SoAir). During 10 h of So oil heating, the α‐tocopherol was depleted and the content of α‐tocopheryl quinone in So grew from 3 to 84 mg/kg, as did the content of tocopherol free fatty acid esters from the initial 5 to 185 mg/kg. In SoAir oil, the rate constants of formation and decomposition of tocopherol degradation products were determined. Accelerated oxidation in SoAir caused depletion of the degradation products of tocopherol after 2 h of heating. The reason for this was significant oxidation and polymerization of fatty acids in SoAir oil. The unique features of this work are the syntheses and spectral analysis of tocopherol oxidation products and the development of a suitable method for quantitative analysis of α‐tocopheryl fatty acids. For the first time, we confirmed formation and degradation of tocopheryl fatty acids during oil heating at frying temperature.Practical applications: All the results presented here, consisting of organic syntheses, qualitative and quantitative analysis of α‐tocopheryl fatty acids as well as oxidation and degradation products of tocopherols and fatty acids, will aid future research focused on the degradation of tocopherols. So far the content of α‐tocopheryl fatty acids has not been determined by GC‐FID or HPLC‐UV. This is why there has been little interest in α‐tocopheryl fatty acids, although they are formed both in culinary treatment of food and in oil refining.Free fatty acids (FFAs), fatty acids (FAs), oxidation [o], products (i) and products (ii) are unspecified products of α‐tocopheryl FAs and α‐TQ degradation. Degradation products of α‐tocopherol were formed in heated sunflower oil and further heating of oil caused decomposition of α‐tocopherol degradation products.

Influence of Lentinus edodes and Agaricus blazei extracts on the prevention of oxidation and retention of tocopherols in soybean oil in an accelerated storage test.

This study aimed to evaluate the influence of the methanol extracts of mushrooms Lentinus edodes and Agaricus blazei on the retention of tocopherols in soybean oil, when subjected to an accelerated storage test. The following treatments were subjected to an accelerated storage test in an oven at 60°C for 15days: Control (soybean oil without antioxidants), TBHQ (soybean oil + 100mg/kg of TBHQ), BHT (soybean oil + 100mg/kg of BHT), L. edodes (soybean oil + 3,500mg/kg of L. edodes extract) and A. blazei (soybean oil + 3,500mg/kg of A. blazei extract). The samples were analyzed for tocopherols naturally present in soybean oil and mass gain. The results showed, the time required to reach a 0.5% increase in mass was 13days for TBHQ and 15days for A. blazei. The content of tocopherols for TBHQ was 457.50mg/kg and the A. blazei, 477.20mg/kg.

Inhibition of the Peroxidation of Liposomal Lipids by Uric Acid Requires Tocopherol

Urate is the major water-soluble low molecular weight antioxidants in serum, contributing about 50% to the antioxidative potential of the serum. Unexpectedly, both urate, as well as the other major antioxidant ascorbate, promote the copper-induced peroxidation of liposomal PUFA. In a previous study it has been shown that ascorbate inhibits copper-induced oxidation of liposomal lipids when the liposomes contain Tocopherol, whereas urate does not. In an attempt to explain these findings we studied the temporal order of events, by monitoring continuously and simultaneously the time-course of formation of oxidation products and the consumption of the various components of the system. The resultant kinetic profiles show that: 1. Both water-soluble antioxidants slightly inhibit the oxidation of tocopherol; 2. Ascorbate becomes oxidized very rapidly (much faster than tocopherol), whereas urate and tocopherol become oxidized simultaneously. 3. In the presence of tocopherol, both urate and ascorbate inhibit copper-induced peroxidation of PUFA. 4. AAPH-induced peroxidation of liposomal PUFA is inhibited by both urate and ascorbate, independent of the presence of tocopherol. Our interpretation of these results contribute to the understanding of the complex, interdependent dependence of the susceptibility of aggregated (unlike soluble) lipids on all the water-soluble antioxidants. This is particularly important for evaluation of the oxidizability of serum lipids when the serum contains excess urate, as in the case of insulin-resistant and obese subjects.

Tocopherol metabolism, oxidation and recycling under high light stress in Arabidopsis

Tocopherols are synthesized and accumulated by all plants and many cyanobacteria. The quenching and scavenging of reactive oxygen species and lipid peroxy radicals by tocopherols can result in the formation of various tocopherol oxidation compounds. A targeted GC/MS profiling method was developed to quantify all tocopherols and pathway intermediates, and 23 potential alpha- and gamma-tocopherol oxidation products. This method was used to study the response of wild-type Arabidopsis (Col) and the tocopherol biosynthetic mutants vte1, vte2 and vte4 during 12 h low- and high-light treatments (LL and HL, 90 and 1500 mumol photon m(-2) sec(-1), respectively) and a subsequent 12 h dark recovery period. All tocopherols and pathway intermediates exhibited HL-dependent increases except 2,3-dimethyl-6-phytyl-1,4-benzoquinone (DMPBQ) in vte1 and beta-tocopherol in Col. Profiling of potential tocopherol oxidation products during HL treatment indicated the presence of only alpha-tocopherolquinol (alpha-TQH(2)) in Col and only gamma-tocopherolquinol (gamma-TQH(2)) in vte4, both of which accumulated to similar levels and with similar kinetics the two genotypes. However, during dark recovery, the level of alpha-TQH(2) in Col decreased several times faster than that of gamma-TQH(2) in vte4, suggesting the presence of biochemical processes with higher specificity for alpha-TQH(2). (14)C-labeled alpha-tocopherolquinone (alpha-TQ) applied to isolated Col chloroplasts was converted to (14)C-alpha-tocopherol, demonstrating the existence of a plastid-based system for recycling oxidized alpha-tocopherol. The accumulation of (14)C-trimethylphytylbenzoquinone (TMPBQ) by isolated vte1 plastids treated with (14)C-labeled alpha-TQ is consistent with the tocopherolquinone-recycling pathway utilizing a yet to be identified plastid-localized dehydratase that converts tocopherolquinone to TMPBQ.

Plasma tocopherols and risk of cognitive impairment in an elderly Italian cohort

BackgroundEvidence that vitamin E may preserve cognitive function in elderly subjects is conflicting. The most abundant and most investigated form of vitamin E in humans is α-tocopherol, but other antioxidant tocopherols (β, γ, and δ) exist in nature. ObjectiveWe aimed to investigate plasma concentrations of the natural tocopherols and the tocopherol oxidation markers α-tocopherylquinone (αTQ) and 5-nitro-γ-tocopherol (5NGT) in relation to cognitive function in the elderly. DesignBaseline plasma tocopherols and their oxidation markers were measured in 761 elderly Italian subjects from a population-based cohort assessed in 1999–2000 for mild cognitive impairment (MCI) and dementia. In 2003–2004, information about cognitive status was collected for 615 of the 666 subjects without baseline cognitive impairment. Tocopherols and oxidation markers were analyzed as plasma absolute values divided by serum total cholesterol because lipids affect their blood availability. Analyses were adjusted for sociodemographic, genetic, lifestyle, and medical confounders. ResultsCompared with the corresponding lowest tertile, the risk of prevalent dementia was higher for the highest tertile of δ-tocopherol÷cholesterol [odds ratio (OR): 3.87; 95% CI: 1.46, 10.27] and αTQ÷cholesterol (4.02; 1.45, 11.14), but the risk of incident dementia was not directly associated with plasma vitamin E metabolites. A U-shaped association, with lower risk for intermediate tertiles, was found for prevalent MCI with 5NGT÷cholesterol (0.39; 0.17, 0.91) and for incident dementia with γ-tocopherol÷cholesterol (hazard ratio: 0.42; 95% CI: 0.22, 0.84). ConclusionsPlasma concentrations of some non-α-tocopherol forms of vitamin E are associated with cognitive impairment in elderly people. However, the associations depend on concurrent cholesterol concentration and need further investigation.

A Novel and Efficient Synthesis of Tocopheryl Quinones by Homogeneous and Heterogeneous Methyltrioxorhenium/Hydrogen Peroxide Catalytic Systems

AbstractA convenient and efficient application of heterogeneous poly(4‐vinylpyridine), poly(4‐vinylpyridine N‐oxide), and polystyrene/methylrhenium trioxide systems for the selective oxidation of tocopherols and tocopherol derivatives to the corresponding ortho‐ and para‐tocopherylquinones is described. Environment friendly, easily available, and low‐cost hydrogen peroxide (H2O2) was used as the oxygen atom donor. The antiviral activity of the newly synthesized tocopherylquinones and their parent tocopherols against influenza A virus is also reported. On the basis of the biological assay, the activity of tocopherols against influenza virus is higher than that showed by the corresponding tocopherylquinones, thus suggesting, for the first time, a drawback effect of the oxidative metabolism on the antiviral activity of these compounds.

Enhancement of intracellular γ-tocopherol levels in cytokine-stimulated C3H 10T1/2 fibroblasts: relation to NO synthesis, isoprostane formation, and tocopherol oxidation

BackgroundStimulation of C3H 10T1/2 murine fibroblasts with interferon-γ(IFN) and bacterial lipopolysaccharide (LPS) generates reactive oxygen and nitrogen species leading to DNA damage, lipid oxidation, and tocopherol oxidation. The tocopherols possess unique chemical and biological properties that suggest they have important roles related to intracellular defense against radical-mediated damage.ResultsDespite increased levels of reactive oxidants and decreased media tocopherol, cellular levels of γ-tocopherol, but not α-tocopherol, were observed to increase significantly when cells were treated with IFN/LPS. Inhibition of nitric oxide (NO) synthesis by a specific inhibitor of inducible NO synthase (iNOS) increased both intracellular α-tocopherol and γ-tocopherol concentrations, but did not significantly alter the reduction in media tocopherol levels caused by IFN/LPS treatment. Both exposure to exogenous NO and cellular synthesis of NO in cell culture increased media levels of 8-epi-prostaglandin F2α, a marker of oxidative lipid damage, whereas inhibition of endogenous NO synthesis reduced media 8-epi-prostaglandin F2α formation to control levels.ConclusionElevated intracellular levels of γ-tocopherol in response to the cellular inflammatory state may indicate that it serves a unique role in minimizing cellular damage resulting from endogenous NO synthesis. Results of the current study suggest that NO is an important mediator of damage within the cell, as well as in the oxidation of both α- and γ-tocopherols. The paradoxical increase in cellular tocopherol associated with the induction of NO synthesis may indicate either enhanced cellular transport/decreased export for tocopherols or recruitment of free tocopherol from tocopherol storage molecules.

Singlet Oxygen Oxidation Rates of ∝‐, γ‐, and δ‐Tocopherols

ABSTRACT: The reaction rate constants of 5 × 10−4 M, 10 × 10−4 M, and 20 × 10−4 M α‐, γ‐, and δ‐tocopherols with singlet oxygen in methylene chloride containing 1 × 10−5 M chlorophyll under light at 25 °C for 60 min were studied. The oxidation of tocopherols determined by a spectrophotometric method showed that the losses of 20 × 10−4 M α‐, γ‐, and δ‐tocopherols after 60 min under light were 21%, 16%, and 9%, respectively. The degradation of α‐, γ‐, and δ‐tocopherols was undetectable in the absence of chlorophyll under light or in the presence of chlorophyll in dark. The losses of tocopherols under light were mainly due to singlet oxygen oxidation. The degradation rates of 20 × 10−4 M α‐, γ‐, and δ‐tocopherols were 6.6 ×10−6 M/min, 5.0 × 10−6 M/min, and 2.9 × 10−6 M/min, respectively. The reaction rates between α‐, γ‐, or δ‐tocopherol and singlet oxygen were 4.1 ×106/M s, 3.3 × 106/M s, and 1.4 × 106/M s, respectively. The singlet oxygen oxidation rate of δ‐tocopherol was significantly lower than α‐ or γ‐tocopherol at α= 0.05. As the electron density in the chromanol ring of tocopherol increased, the singlet oxygen oxidation was increased.

Determination of tocopherols, tocopherolquinones and tocopherolhydroquinones by gas chromatography–mass spectrometry and preseparation with lipophilic gel chromatography

Lipophilic gel chromatography using Sephadex LH-20 helps in separating α-, β-+γ-, and δ-tocopherol and also in separation of their oxidation products e.g. the tocopherolquinones or other oxidation products. This preseparation can help to overcome analytical problems due to the complexity of synthesis mixtures of tocopherol oxidation procedures as well as in separation of complex physiological matrices. Determination of the preseparated tocopherols, tocopherolquinones and tocopherolhydroquinones can then be achieved by means of GC–MS measurement of the free substances or their trimethylsilyl derivatives.

Modeling of alpha-tocopherol loss and oxidation products formed during thermoxidation in triolein and tripalmitin mixtures.

The degradation of alpha-tocopherol and the formation of alpha-tocopherol and triacylglycerol oxidation products at high temperatures (150-250 degrees C) over a heating period (0-4 h) for a model system ranging between triolein and tripalmitin were modeled by use of an experimental design. The oxidation products of alpha-tocopherol formed under these conditions were alpha-tocopherolquinone (1 .4-7.7%) and epoxy-alpha-tocopherolquinones (4.3-34.8%). The results indicate a very high susceptibility of alpha-tocopherol to capture peroxyl radicals upon oxidation, leading to the formation of polar tocopherol oxidation products. Both alpha-tocopherolquinone and epoxy-alpha-tocopherolquinones were not stable upon prolonged heating and were further degraded to other unknown oxidation products. The kinetics of alpha-tocopherol oxidation were significantly influenced by the triolein/tripalmitin ratio. By increasing the level of triacylglycerol unsaturation the rate of alpha-tocopherol recovery after heating increased significantly from 2.2 to 44.2% whereas in the meantime triacylglycerol polymerization increased from 0 to 3.7%.

Coenzyme Q10, vitamin E, and dihydrothioctic acid cooperatively prevent diene conjugation in isolated low-density lipoprotein.

Coenzyme Q (Q10) and alpha-tocopherol cooperatively delay the onset of diene conjugation in isolated human low density lipoprotein if supplied in water-soluble preparations to blood serum. Both copper ions and morpholino sydnonimine (in the presence of glucose; SIN-1-glucose) -driven diene conjugation is measurable as soon as both reduced Q10 and tocopherol are oxidized, where tocopherol oxidation starts after 80-90% consumption of reduced Q10. LDL-bound Q10 in turn can be rapidly reduced by dihydrolipoic acid (thioctic acid). This reaction is at least 10 times faster than reduction by ascorbic acid.

Bicarbonate Enhances the Peroxidase Activity of Cu,Zn-Superoxide Dismutase: ROLE OF CARBONATE ANION RADICAL

We examined the effect of bicarbonate on the peroxidase activity of copper-zinc superoxide dismutase (SOD1), using the nitrite anion as a peroxidase probe. Oxidation of nitrite by the enzyme-bound oxidant results in the formation of the nitrogen dioxide radical, which was measured by monitoring 5-nitro-gamma-tocopherol formation. Results indicate that the presence of bicarbonate is not required for the peroxidase activity of SOD1, as monitored by the SOD1/H(2)O(2)-mediated nitration of gamma-tocopherol in the presence of nitrite. However, bicarbonate enhanced SOD1/H(2)O(2)-dependent oxidation of tocopherols in the presence and absence of nitrite and dramatically enhanced SOD1/H(2)O(2)-mediated oxidation of unsaturated lipid in the presence of nitrite. These results, coupled with the finding that bicarbonate protects against inactivation of SOD1 by H(2)O(2), suggest that SOD1/H(2)O(2) oxidizes the bicarbonate anion to the carbonate radical anion. Thus, the amplification of peroxidase activity of SOD1/H(2)O(2) by bicarbonate is attributed to the intermediary role of the diffusible oxidant, the carbonate radical anion. We conclude that, contrary to a previous report (Sankarapandi, S., and Zweier, J. L. (1999) J. Biol. Chem. 274, 1226-1232), bicarbonate is not required for peroxidase activity mediated by SOD1 and H(2)O(2). However, bicarbonate enhanced the peroxidase activity of SOD1 via formation of a putative carbonate radical anion. Biological implications of the carbonate radical anion in free radical biology are discussed.

Influence of ecological cultivation on virgin olive oil quality

AbstractThe quality of oil extracted from ecologically cultivated olives of the Picual variety was compared with oil extracted from Picual olives cultivated using conventional methods. Olive trees were grown in a two‐section plot. Fruits from each plot were harvested at various stages of ripeness, and acidity value, peroxide index, ultraviolet absorption at 232 and 270 nm, stability to oxidation, sensory analysis, fatty composition, and contents of tocopherols, phenolic compounds, and sterols were determined on oil extracted from each treatment. The results showed that the organic virgin olive oil was of a superior quality to the conventional virgin olive oil in all the quality parameters analyzed.

Effects of α‐ and γ‐tocopherols on the autooxidation of purified sunflower triacylglycerols

The antioxidant effects of alpha- and gamma-tocopherols were evaluated in a model system based on the autooxidation of purified sunflower oil (p-SFO) triacylglycerols at 55 degrees C for 7 d. Both tocopherols were found to cause more than 90% reduction in peroxide value when present at concentrations >20 ppm. Alpha-tocopherol was a better antioxidant than gamma-tocopherol at concentrations < or =40 ppm but a worse antioxidant at concentrations >200 ppm. Neither alpha- nor gamma-tocopherol showed a prooxidant effect at concentrations as high as 2000 ppm. The amount of tocopherols consumed during the course of oxidation was positively correlated to the initial concentration of tocopherols, and the correlation was stronger for alpha- than for gamma-tocopherol. This correlation suggested that, besides reactions with peroxyl radicals, destruction of tocopherols may be attributed to unknown side reactions. Addition of FeSO4, as a prooxidant, caused a 12% increase in the peroxide value of p-SFO in the absence of tocopherols. When tocopherols were added together with FeSO4, some increase in peroxide value was observed for samples containing 200, 600 or 1000 ppm of alpha- but not gamma-tocopherol. The addition of FeSO4, however, caused an increase in the amount of alpha- and gamma-tocopherols destroyed and led to stronger positive correlations between the amount of tocopherols destroyed during oxidation and initial concentration of tocopherols. No synergistic or antagonistic interaction was observed when alpha- and gamma-tocopherols were added together to autooxidizing p-SFO.