The effect of various concentrations of tocopherols and tocopherol mixtures on the oxidative stability of a sample of lard

A comparison was made of α-, γ-, and δ-tocopherol at various concentrations and a mixture of these tocopherols representing the average tocopherol content of peanut oil on the oxidative stability of lard at 97C. Uptake of oxygen was used to indicate the length of the induction period. The antioxidant effectiveness of the tocopherols was found to increase in the order α, δ, γ. The antioxidant efficiency decreases with increasing concentrations of tocopherols such that addition of any single tocopherol above a concentration of 250 μg/g has little effect on oxidative stability. A mixture equivalent to that of an average peanut oil sample, containing 150 μg/g of α-tocopherol and 250 μg/g of γ-tocopherol and 15 μg/g of δ-tocopherol was found to be no more stable than one containing 250 μg/g of γ-tocopherol alone.     

Interaction of Light and Temperature on Tocopherols During Oxidation of Sunflower Oil

Light and temperature effects on tocopherols during the oxidation of sunflower oil were studied. The oxidation was performed at 40, 60, or 80 °C for 30, 15, and 6 days, respectively, in the dark or under 1,700 lux light. Oil oxidation was analyzed with peroxide values and conjugated dienoic acid contents, and tocopherols in the oil were separated and quantified by HPLC. The oxidation of sunflower oil was increased with temperature increase, and the light decreased the temperature dependence of the oil oxidation. Sunflower oil before oxidation contained tocopherols with a total of 737.96 mg/kg, with α- and γ-tocopherol at 726.41 and 11.56 mg/kg, respectively, and the tocopherol contents decreased during the oil oxidation. Degradation of tocopherols increased with the temperature increase, and its dependence on the temperature was lower under light than in the dark. γ-Tocopherol showed higher stability than α-tocopherol during oxidation of the oil in the dark and under light. Residual amounts of tocopherols showed a relatively good correlation with the degree of oil oxidation, and the dependence of α-tocopherol degradation on the oil oxidation was higher than that of γ-tocopherol, and light decreased the dependence on the oil oxidation in both tocopherols.     

Stability of Tocopherol Homologs in Bulk Oils at 60°C Oxidation and Chlorophyll Photosensitization by the Action of Moisture

The effects of deuterium oxide (D₂O) on the stability of tocopherol homologs were evaluated in corn oil stored at 60°C or in the process of chlorophyll photosensitization. The degree of oxidation, changes in moisture, and the levels of tocopherol homologs were analyzed. The moisture content in corn oil incubated with deuterium-free water (H₂O) was significantly (P < 0.05) higher than that in corn oil incubated with D₂O. The presence of D₂O accelerated the rate of lipid oxidation in corn oil, irrespective of whether it has been oxidized at 60°C or has been photosensitized by chlorophyll. After exposure to either of the oxidative stresses, the stability of β + γ-tocopherols present in corn oil was enhanced in the presence of D₂O compared to corn oil incubated in the presence of H₂O, or control corn oil without the addition of moisture. However, the stability of α-tocopherol in corn oil incubated with D₂O was significantly lower after oxidation at 60°C compared to the other conditions (P < 0.05), whereas it was significantly higher than under the other conditions after chlorophyll photosensitization (P < 0.05). The moisture and type of oxidative stress, therefore, play important roles in the stability of tocopherol homologs in bulk oils.     

Effect of Roasting on Flaxseed Oil Quality and Stability

The food industry is interested in the application of roasted flaxseeds because the treatment improves their sensory acceptability. However, it also influences flaxseed oil nutritional quality and stability. The aim of the study was to analyze oxidation changes in situ and in flaxseed oil compounds (fatty acids, phytosterols, tocochromanols) and Maillard reaction products (MRP) after roasting. The effect of the roasting temperature (160–220 °C) and flaxseed cultivars (golden- and brown-seed) was taken into consideration. The results showed that the selection of roasting temperature (<200 °C vs. ≥200 °C) and flaxseed cultivar significantly influenced the nutritional quality and oxidative stability of roasted flaxseed oils. The roasting of flaxseeds did not significantly affect the fatty acid profiles of oil but it influenced the content of the other bioactive compounds. As the roasting temperature increased (≥200 °C), the γ-tocopherol degradation decreased, whereas the content of plastochromanol-8 increased. The total content of phytosterols in the roasted seed samples was higher than in the raw seeds but there was no correlation between the phytosterol content and roasting temperature. The temperature ≥200 °C significantly accelerated in situ oil oxidation during roasting. On the other hand, these conditions favored the MRP formation, which may have slowed down the dynamics of oil oxidation during storage. There was lower oil oxidation in the brown-seed cultivar; in consequence, the tocopherol retention was higher than in the golden-seed cultivars. The results could be useful for the selection of the best cultivars and treatment conditions to decrease unfavorable changes in flaxseed oil nutritional quality and stability.     

Role of Tocopherol as an Antioxidant in Safflower Oil

In a mixture of oleic and linoleic acids in equal proportions, the latter dominates the autoxidation pattern. At 63° C, γ-tocopherol offered the best protection to linoleate-rich substrates, with α-and δ-next in order. Safflower oil is insufficiently protected by its own tocopherols. Doubling the tocopherol content by supplementation or increasing the cephalin content effected only slight improvement. Safflower oil is best stabilized by a combination of synthetic phenolic antioxidants and synergists.     

Antioxidant Activity of Added Phenolic Compounds in Freeze-Dried Microencapsulated Sunflower Oil

This study was aimed at evaluating the effectiveness of phenolic antioxidants with a similar structure but having a different polarity in dried microencapsulated sunflower oil. The antioxidants tested were, on one hand, α-tocopherol and its water soluble analogue, Trolox, and on the other, gallic acid and its ester derivatives, propyl gallate and dodecyl gallate. At a moderate temperature (40 °C), the samples were oxidized under accelerated conditions by using Cu(II) as an oxidation catalyst. The progress of oxidation was followed up over time in the free and encapsulated oil fractions. The peroxide value, the total content of polymers and, when appropriate, the content of α-tocopherol were determined. Quantitative analysis of the total fraction of the non-volatile oxidation products and their distribution in oligomers, dimers and monomers was applied to samples to obtain a complete evaluation of oxidation. Finally, as a complementary measure, the antioxidants were also assessed by direct application of the Rancimat test at 100 °C on the dried microencapsulated oil samples. Results showed that the antioxidants of lower polarity in each series, i.e. tocopherol and dodecyl gallate, were to a great extent the most protective antioxidants. The results obtained by the Rancimat test were consistent with those found during oxidation at moderate temperature. Furthermore, the addition of Cu(II) reduced proportionally the oxidative stability index of the dried microencapsulated samples.     

Behavior of alpha,gamma, and delta tocopherols with linoleic acid in aqueous media

Tocopherols can exhibit opposite effects in aqueous media on linoleic acid autoxidation rate. The effect which was observed depended on tocopherol concentration and on the tocopherol itself. At 0.05 mole of tocopherol per mole of linoleic acid, α-tocopherol was prooxidant while in similar conditions, δ-tocopherol was anti-oxidant as well as γ-tocopherol. However, this latter one exhibited a slight antioxidant activity. When tocopherol concentration decreased (twice as weak), α-tocopherol still exhibited the same pro-oxidant activity, while the antioxidant effect of γ and δ tocopherols was increased. The study of tocopherol stability by HPLC has shown that tocopherol oxidation increased in order δ < γ < α. There was a relationship between the ability for a tocopherol to be easily oxidized by air and its prooxidant activity. Tocopherol oxidation would enhance the formation of a perhydroxyl radical ([·OOH] or one of this type [O₂0=, ·OH]) which was responsible for the prooxidant effect.     

Properties of α-, γ-, and δ-tocopherol in purified fish oil triacylglycerols

The effect of α-tocopherol (αTOH) (50–2000 ppm), γ-tocopherol (γTOH) (100–2000 ppm), and δ-tocopherol (δTOH) (100–2000 ppm) on the formation and decomposition of hydroperoxides in purified fish oil triacylglycerols (TAG) was studied. The tests were conducted at 30°C in the dark. Purified fish oil TAG oxidized very rapidly with no apparent induction period. The relative ability of the tocopherols to retard the formation of hydroperoxides decreased in the order αTOH> γTOH>δTOH at a low level of addition (100 ppm), but a reverse order of activity was found when the initial tocopherol concentration was 1000 ppm. This dependence of relative antioxidant activity on tocopherol concentration was caused by the existence of concentrations for maximal antioxidant activity for αTOH and for γTOH. An inversion of activity, on the basis of hydroperoxide formation, was observed for αTOH at 100 ppm and for γTOH at 500 ppm, whereas the antioxidant activity of δTOH increased with level of addition up to 1500–2000 ppm. None of the tocopherols displayed any prooxidant activity. All three tocopherols strongly retarded the formation of volatile secondary oxidation products in a concentration-dependent manner. At concentrations above about 250 ppm there appeared to be a linear relationship between rate of consumption of αTOH and initial αTOH concentration, in accordance with the linear relationship observed between the initial rate of formation of hydroperoxides and the initial αTOH concentration. The rate of consumption of γTOH also increased with initial concentration, but to a lesser extent than for αTOH. At high levels of addition the rate of consumption of δTOH was independent of initial concentration, appearing to reflect the greater stability of this tocopherol homolog and participation in reactions with lipid peroxyl radicals only. Presented in part at the AOCS annual meeting in San Diego, California, April 2000.     

Antioxidant activities of α- and γ-tocopherols in the oxidation of rapeseed oil triacylglycerols

Antioxidant properties of 5 to 500 μg/g levels of α-and γ-tocopherols, in the oxidation of rapeseed oil triacylglycerols (RO TAG), were studied at 40°C in the dark. Each tocopherol alone and in a mixture was studied for its stability in oxidizing RO TAG. Also the effects of tocopherols on the formation of primary and secondary oxidation products of RO TAG were investigated. Both tocopherols significantly retarded the oxidation of RO TAG. At low levels (≤50 μg/g), α-tocopherol was more stable and was a more effective antioxidant than γ-tocopherol. At higher α-tocopherol levels (>100 μg/g), there was a relative increase in hydroperoxide formation parallel to consumption of α-tocopherol, which was not found with γ-tocopherol. Therefore, γ-tocopherol was a more effective antioxidant than α-tocopherol at levels above 100 μg/g. As long as there were tocopherols present, the hydroperoxides were quite stable and no volatile aldehydes were formed. In a mixture, α-tocopherol protected γ-tocopherol from being oxidized at the addition levels of 5+5 and 10+10 μg/g but no synergism between the tocopherols was found. α-Tocopherol was less stable in the 500+500 μg/g mixture than when added alone to the RO TAG. No prooxidant activity of either tocopherol or their mixture was found.     

Evaluating Electron Paramagnetic Resonance (EPR) to Measure Lipid Oxidation Lag Phase for Shelf-Life Determination of Oils

Lipid oxidation is one of the major causes of oil deterioration causing off-flavors and consumer rejection. Fast, easy, and dependable assays for predicting lipid oxidation rates in foods are important for shelf-life prediction. In this study, an electron paramagnetic resonance (EPR) spin-trapping technique with N-tert-butyl-α-phenylnitrone (PBN) was tested to determine the lag phase of lipid oxidation in stripped soybean oil (SSO), SSO with added α-tocopherol, and commercial soybean, canola and corn oils. EPR intensity of spin-trapped products from SSO correlated well with lipid hydroperoxides formation for samples stored at 37 and 55 °C respectively. When the antioxidant α-tocopherol was added, the EPR signal intensity of oil samples increased—indicating sample deterioration—after 50–65% of α-tocopherol was consumed. When using the EPR method with commercial soybean, canola or corn oil stored at 55 °C, there was a poor relationship between EPR intensity and lipid hydroperoxides lag phases. However, a linear correlation was found between EPR signal intensity and hexanal formation. For example, EPR signal intensity lag phases were 5, 13 and 27 days for soybean, canola and corn oils, respectively which was similar to the hexanal lag phases of 5, 13 and 25 days for the same oils. The EPR spin-trapping assay method has several advantages over headspace hexanal measurements, especially with regard to easier sample handling and shorter analysis times.     

Effect of processing on the oxidative stability of low erucic acid turnip rapeseed (Brassica rapa) oil

The effect of various processing conditions on the composition and the oxidative stability of mechanically pressed (90–95°C) rapeseed oil was investigated. The five different rapeseed oils included crude (nondegummed), superdegummed, steam stripped (at 140°C for 4h, nondegummed), physically refined (degummed, bleached and deodorized at 240°C), and cold pressed (40°C) oils. Oils were autoxidized in the dark at 60°C and under light at 25°C. Oxidation was followed by measuring changes in the peroxide values (PV) and the consumption of tocopherol and carotenoid was measured. In the dark the oils reached PVs of 10 meq/kg in the order: cold pressed > superdegummed > steam stripped ≅ crude > refined. However, under light conditions the order changed as follows: cold pressed > crude ≅ steam stripped > superdegummed > refined. Processing had no effect on fatty acid composition nor α-tocopherol content of the oils. Superdegumming and steam stripping decreased the carotenoid content of the oils while cold pressing and refining reduced also chlorophyll, γ-tocopherol and phosphorus content of the oils.     

Antioxidant Activities and Oxidative Stabilities of Some Unconventional Oilseeds

The oils of some unconventional oilseeds (hemp, radish, terebinth, stinging nettle, laurel) were obtained by a cold-press method in which the total oil content, fatty acids, tocopherol isomers, some metal contents (Ca, Mg, Fe, Cu), antioxidant activity and oxidative stability were determined. The total oil content was determined ranging between 30.68 and 43.12%, and the oil samples had large amounts of unsaturated fatty acids, with oleic acid and linoleic acid. Of all the oils, terebinth seed oil had the highest α-tocopherol content (102.21 ± 1.01 mg/kg oil). Laurel oilseed had the highest antiradical activity in both the DPPH and ABTS assays. The peroxide value of the non-oxidized oils ranged between 0.51 and 3.73 mequiv O₂/kg oil. The TBARS value of the non-oxidized oils ranged between 0.68 ± 0.02 and 6.43 ± 0.48 mmol MA equiv/g oil. At 110 °C, the Rancimat induction period of the oils ranged between 1.32 and 43.44 h. The infrared spectra of the samples were recorded by FTIR spectroscopy. The absorbance values of the spectrum bands were observed and it was determined that some of the chemical groups of oxidized oils caused changes in absorbance. As a result of the present research, the analyzed oils could be evaluated as an alternative to traditionally consumed vegetable oils or as additives to them.     

Influence of used frying oil quality and natural tocopherol content on oxidative stability of fried potatoes

Sunflower oil (SO) and high-oleic sunflower oil (HOSO) were used to prepare fried potatoes by either discontinuous or continuous laboratory frying. Fried potatoes that had been fried in oils of differing quality were stored at 60°C for up to 30 d and evaluated for polar compounds, polymers, peroxide value, oil stability index, and α-tocopherol content. Results obtained through the various methods applied were consistent and indicated that the length of the induction period could not be explained only on the basis of the degree of unsaturation or polar compound levels in fried potatoes before storage. α-Tocopherol content also had a significant influence as potatoes fried in HOSO, with 16% polar compounds and only 10 mg/kg α-tocopherol at the starting point of storage, were oxidized more rapidly than potatoes fried in SO with a comparatively higher degradation level, 19% polar compounds, and 100 mg/kg α-tocopherol.     

Cultivar Characterization of Tea Seed Oils by Their Active Components and Antioxidant Capacity

Cultivar characterization of tea seed oils based on their active components and antioxidant capacity was carried out, providing fundamental data for authentication. The seeds were collected from 28 cultivars grown under the same conditions in the region of Anxi county of Fujian province and their oils were analyzed. The results showed that total phenols content (TPC), total flavonoids content, α-tocopherol contents, γ-tocopherol content and δ-tocopherol content were 16.7–529.3 mg GAE/kg of oil, 4.4–208.7 mg rutin/kg of oil, 7.7–347.1 mg/kg of oil, 1.8–106.7 mg/kg of oil, 0.003–35.769 mg/kg of oil, respectively. The antioxidant capacity measured by DPPH radical scavenging activity (DPPH), oxygen radical absorbance capacity (ORAC), absorbance of protein carbonyl (APC) and the absorbance of protein hydroperoxides (APH) were 91.0–2,164.5 μmol/100 g of oil, 251.0–1,209.5 μmol/100 g of oil, 0.014–0.135, 0.034–0.458, respectively. The correlation analysis revealed that the presence of phenolic compounds was significantly correlated with the antioxidant capacity of tea seed oil. Principal Component Analysis revealed the first three components accounted for 81.31 % of the total variance within the data and the main contributor parameters were DPPH, ORAC, APC, APH and TPC. Hierarchical cluster analysis classified the cultivars into three groups, which were in line with the genetic relationship among the cultivars. Our results supplied basic data for the antioxidant mechanism research of tea seed oil and provided necessary information to develop a breeding program directed to tea seed cultivar selections with the high nutraceutical value of tea seed oil.     

Thermal Stability of Rapeseed Oil Fortified with Unsaturated Fatty Acid Sterol Esters

The thermal stability of rapeseed oil fortified with 3 % sterol linolenate, sterol linoleate, and sterol oleate was investigated using the Rancimat accelerated oxidation method. The results indicated that the sterol ester content in fortified oil displayed positive correlations (P < 0.05) with total phenols and tocopherols and significant negative correlations (P < 0.05) with acid value (AV), peroxide value (POV), conjugated diene value, \(\varDelta E\) value, viscosity, and polyphenols and γ-tocopherol levels. The sterol ester content in fortified oil was found to significantly decrease when the oil was heated at 110 °C. The rate of increase of the AV, POV, \(\varDelta E\) value, and viscosity, and the rate of decrease of polyunsaturated fatty acid, tocopherol, and polyphenol contents were accelerated with the increase of the degree of unsaturation of fatty acid sterol esters in rapeseed oil during heating. Therefore, the oxidative stability is further reduced by increasing the degree of unsaturation, as the instability of fortified oil is mainly due to the decomposition of unsaturated fatty acid sterol esters. The addition of lipid-soluble polyphenols is an effective method to improve the stability of rapeseed oil fortified with unsaturated fatty acid sterol esters.     

Partitioning of ρ-tocopherol in aqueous mixtures of TAG and isolated muscle membranes

To study the uptake of ρ-tocopherol by aqueous suspensions of membranes isolated from chicken muscle and the partitioning of the antioxidant in mixtures of chicken TAG and membranes, ρ-tocopherol was added to suspensions of these components and they were centrifuged. In an aqueous suspension of membranes only, the tocopherol uptake increased linearly with tocopherol concentration, at about 50% of the added ρ-tocopherol at all concentrations. The incorporation of tocopherol into the membranes was independent of incubation temperature in the range of 0–37°C. Studies with aqueous mixtures of membranes and TAG suggested a very low exchange of tocopherol between the different lipid fractions upon mixing when the tocopherol resided initially in one lipid fraction. Adding ρ-tocopherol in ethanol favored incorporation of the antioxidant into the membranes; little antioxidant was incorporated into the membranes when it was added to the suspensions in oil. The results suggest that partitioning of exogenous ρ-tocopherol between TAG and membrane lipids in muscle foods may be controlled in part by proper selection of the solvent in which it is added.     

Antioxidant Evaluation of Coriander Extract and Ascorbyl Palmitate in Sunflower Oil Under Thermoxidation

The objectives of this study were to evaluate isolated and synergistic antioxidant effects of coriander extract and ascorbyl palmitate (AP) in sunflower oil subjected to thermoxidation, and to verify their influence on the oxidative resistance of α-tocopherol, which occurs naturally in safflower oil. Sunflower oil samples with 1,600 mg/kg coriander extract, 500 mg/kg AP, and a mixture of those two antioxidants were heated to 180 °C for 30 h. Samples were taken at 0, 10, 20 and 30 h and analyzed to evaluate oxidative stability, total polar compounds, and α-tocopherol content. Results were subjected to variance analyses and Tukey tests at a 5% significance level, in a factorial scheme, to an entirely casual delineation. Coriander extract and AP delayed lipid oxidation and promoted the retention of α-tocopherol when added separately to sunflower oil and subjected to thermoxidation. The mixture of the antioxidants showed a higher antioxidant effect, thereby demonstrating their synergy under these conditions.     

Antioxidant activity of green teas in different lipid systems

Different commercial green teas from Japan, China, and India, were compared in different lipid systems. Green teas were active antioxidants in bulk corn oil oxidized at 50°C but were prooxidant in the corresponding oil-in-water emulsions. Green teas also were active antioxidants in soybean lecithin liposomes oxidized at 37°C in the presence of cupric acetate as catalyst. At 50°C, however, three of the samples of green tea were active antioxidants in the absence of copper catalyst, and two samples showed prooxidant activity in the presence of copper catalyst. The marked variation in activity among green tea samples may be due partly to differences in their relative partition between phases in different lipid systems. The improved antioxidant activity observed for green teas in lecithin liposomes compared to corn oil emulsions can be explained by the greater affinity of the polar tea catechin gallates for the polar surface of the lecithin bilayers, thus affording better protection against oxidation. Liposomes may thus be appropriate lipid models to evaluate antioxidants for foods containing phospholipids.     

Lipid composition and oxidative stability of oils in hazelnuts (Corylus avellana L.) grown in New Zealand

Hazelnut (Corylus avellana L.) samples were collected from six different cultivars of trees grown in an experimental orchard at Lincoln University. Three U.S. commercial cultivars (Butler, Ennis, and Barcelona), two European commerical cultivars (Tonda di Giffoni and Campanica), and one New Zealand selection (Whiteheart) were evaluated. The total oil, stability to oxidation of the oil, and fatty acid, tocopherol, and sterol composition were determined on samples of freshly extracted hazelnut oil. The total oil content of the seeds ranged from 54.6 to 63.2% while the stability of the oil, as measured by the Rancimat test ranged from 15.6 to 25.3 h. The content of the monounsaturated oleic acid in the oils ranged from 73.8 to 80.1% of the total fatty acids, while the tocopherol content ranged from 225.8 to 552.0 mg/g freshly extracted oil. The major desmethylsterols were sitosterol, ranging from 1416 to 1693 μg/g, campesterol, ranging from 78 to 114 μg/g, and Δ5-avenasterol, ranging from 110 to 170 μg/g. The oil extracted from the cultivar Whiteheart was more stable (measured by Rancimat) than the oil from all other cultivars grown at the same location and under the same conditions. Whiteheart contained higher levels of total and γ-tocopherol when compared to the other cultivars. The higher levels of tocopherol in Whiteheart help to explain the greater stability of the oil during the oxidative stress test. These results suggest that nuts from the cultivar Whiteheart could be stored longer than the other nuts tested. Presented as a poster at the 87th AOCS Annual Meeting, Indianapolis, Indiana, April 28–May 1, 1996.     

Environmental and Genetic Variation of Soybean Tocopherol Content Under Brazilian Growing Conditions

Information about the chemical composition of soybean cultivars (cvs) and environmental impact on their composition is important for processors and exporters to meet the demand of niche markets. Tocopherol composition (α, β, γ, δ, and total), was analyzed in seeds of 89 Brazilian soybean cultivars grown under fertile soil in Ponta Grossa, Paraná state, Brazil, in 2001. A large range of variability was observed: for α-tocopherol, 11 ppm (cv. Davis) to 191 ppm (cv. IPB-T); for β-tocopherol, 6 ppm (cv. IAC 1) to 64 ppm (cv. IPB-T); for γ-tocopherol, 304 ppm (BR62 Carla) to 1333 ppm (cv. Bienville); for δ-tocopherol, 174 ppm (cv. UFV 15) to 580 ppm (cv.IAS-5; and for total tocopherols, 561 ppm (cv. BRS62 Carla) to 1,983 ppm (cv. BR4-RC). For comparison of different growing locations, cv. MG/BR 46 Conquista was grown in 16 different locations of the Minas Gerais and Goiás states (Central Region, ca. 17° South latitude). Higher content of total tocopherol was found in Conquista, Uberaba, Sacramento, and Cerrado, while lower contents were observed in Alvorada, Iraí, and Uberlândia. In the South region (ca. 23° South latitude), the cultivar IAS 5, grown in 12 different locations of Paraná and São Paulo states, showed high total tocopherol content in Londrina, Pedrinhas, Ponta Grossa, and Nuporanga, and lower amounts in Cascavel, Pirassununga, Luiziana, and Morro Agudo. Tocopherol content in soybean seeds varied due to genetic differences as well as to the local environmental factors of different growing locations.