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

Temperature dependence of autoxidation of perilla oil and tocopherol degradation

Temperature dependence of the autoxidation of perilla oil and tocopherol degradation was studied with corn oil as a reference. The oils were oxidized in the dark at 20, 40, 60, and 80 degrees C. Oil oxidation was determined by peroxide and conjugated dienoic acid values. Tocopherols in the oils were quantified by HPLC. The oxidation of both oils increased with oxidation time and temperature. Induction periods for oil autoxidation decreased with temperature, and were longer in corn oil than in perilla oil, indicating higher sensitivity of perilla oil to oxidation. However, time lag for tocopherol degradation was longer in perilla oil, indicating higher stability of tocopherols in perilla oil than in corn oil. Activation energies for oil autoxidation and tocopherol degradation were higher in perilla oil (23.9 to 24.2, 9.8 kcal/mol, respectively) than in corn oil (12.5 to 15.8, 8.8 kcal/mol, respectively) indicating higher temperature-dependence in perilla oil. Higher stability of tocopherols in perilla oil was highly related with polyphenols. The study suggests that more careful temperature control is required to decrease the autoxidation of perilla oil than that of corn oil, and polyphenols contributed to the oxidative stability of perilla oil by protecting tocopherols from degradation, especially at the early stage of oil autoxidation.

Tocopherol, carotene, phenolic contents and antibacterial properties of rose essential oil, hydrosol and absolute

The antioxidant and antibacterial activities, and total phenolic contents of Rosa damascena Mill. flower extracts (absolute, essential oil and hydrosol) were investigated. The chemical compositions of these extracts were analysed by GC-MS. Phenylethyl alcohol (78.38%) was found to be the main constituent of rose absolute, while citrenellol and geraniol were the major compounds (>55%) of rose essential oil and hydrosol. Tocopherol and carotene levels were determined by high performance liquid chromatography (HPLC) analysis. The levels of beta carotene (422.3+/-35.6 ppm), alpha tocopherol (2397.1+/-72.5 ppm) and gamma tocopherol (343.1+/-28.4 ppm) of rose absolute were found to be higher than that of essential oil and hydrosol. Their total phenolic contents were also evaluated. The total phenolic content of the tested extracts varied from 5.2 to 2134.3 GAE/mg L(-1). Rose absolute and essential oil contained high levels of phenolics and demonstrated strong antibacterial activity against Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), Bacillus subtilis (ATCC 6633), Staphylococcus aureus (ATCC 6538), Chromobacterium violaceum (ATCC 12472) and Erwinia carotovora (ATCC 39048) strains.

Systematic evaluation of the antioxidant potential of different parts of Foeniculumvulgare Mill. from Portugal

Fennel (Foeniculum vulgare Mill.) is a widespread perennial umbeliferous (Apiaceae) herb, traditionally used for medicinal purposes and human consumption. It is highly recommended for diabetes, bronchitis and chronic coughs, and for the treatment of kidney stones; some of those chronic diseases are related to the production of radical species involved in the oxidative stress. Therefore, the antioxidant potential of this herb might explain some of their empirical uses in folk medicine. This is the first time that a systematic study on different parts of fennel is performed, in order to understand differences in the antioxidant potential of shoots, leaves, steams, and inflorescences, particularly related to their composition in antioxidant compounds such as vitamins (ascorbic acid and tocopherols) and phenolics. The shoots seems to have the highest radical-scavenging activity and lipid peroxidation inhibition capacity (EC(50) values<1.4 mg/ml), which is in agreement with the highest content in phenolics (65.85+/-0.74 mg/g) and ascorbic acid (570.89+/-0.01 microg/g) found in this part. The shoots also revealed high concentration of tocopherols (34.54+/-1.28 microg/g) and were the only part with flavonoids.

Effect of type of oil and addition of delta-tocopherol on model flavor compound stability during storage

The objective of this study was to investigate approaches to protect selected flavor compounds from deterioration when stored in an oil matrix. An aroma compound model mixture was prepared in a medium-chain triglyceride (MCT) or sunflower oil (SfO) matrix and stored under either an ambient air or argon atmosphere containing, respectively, ca. 20 and <0.5% residual oxygen as controls or containing a natural antioxidant, delta-tocopherol (0.01%). Samples were analyzed by static headspace GC/FID to determine the stability over time of the compounds in mixture. It was found that the type of oil had the greatest effect (P < 0.01) on overall compound stability. A low-oxygen atmosphere also had a significant (P < 0.05) protective effect on the aroma compounds in both oils. The addition of delta-tocopherol generally offered little additional protection. No significant relationship could be determined between the oxidation of the lipid matrix and the loss of oxidation-sensitive thiol compounds.

NIR spectroscopy and partial least-squares regression for determination of natural alpha-tocopherol in vegetable oils

Near-infrared (NIR) spectroscopy and partial least-square regression were used for determination of alpha-tocopherol in edible oils after extraction with ethanol. The standard error of calibration and the standard error of prediction were calculated for evaluation of the calibration models. The chemometric calibration model was prepared in spectral region 6500-4500 cm(-1) for standard alpha-tocopherol solutions (0.54-53.54 mg/mL). Obtained mean concentrations of natural alpha-tocopherol in different types of oils varied from 17.53 to 57.10 mg/100 g. Net analyte signal calculation was used to estimate detection limit (DL = 0.12 mg/mL), quantification limit (QL = 0.40 mg/mL), sensitivity (SEN = 0.045 mg/mL), and selectivity (SEL ranged between 0.24 and 0.54% of the measured reflectance signal) of the proposed NIR method. The comparable precision (RSD = 0.68-2.80% and 0.79-3.06%) and accuracy (recovery, 97.2-102.4% and 96.8-103.2%) for the proposed NIR and standard HPLC methods, demonstrate the benefit of the NIR method in the routine analysis of alpha-tocopherol in vegetable oils.

The more--the better? Estimating the inhibitory activity of alpha-tocopherol towards lipid oxidation

Tocopherols are considered to be powerful antioxidants, but prooxidative effects are discussed for higher concentrations. The aim of this in vitro study was to investigate the dose-dependent inhibition of oxidation product formation caused by alpha-tocopherol, and to estimate the range of maximum antioxidant activity of alpha-tocopherol at different stages of lipid oxidation. Alpha-tocopherol was added to rapeseed oil triglycerides (ROTG, purified rapeseed oil) in concentrations ranging from 25 to 1500 micromol/kg ROTG. The inhibitory activity of alpha-tocopherol increased up to a concentration of 100 micromol/kg ROTG. A concentration of 125 micromol alpha-tocopherol/ kg ROTG did not result in an improved antioxidant effect. The formation of volatile secondary oxidation products followed the same trend, and the maximum inhibitory effect was also found for 100 micromol alpha-tocopherol/kg. Further, concentrations between 250 and 1500 micromol alpha-tocopherol/kg ROTG clearly caused increased formation of hydroperoxides during the induction period. However, compared to the control, all tested alpha-tocopherol concentrations resulted in a reduction of hydroperoxide formation and no prooxidative effects were observed.

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%.

Effects of alpha-tocopherol and ascorbyl palmitate on the isomerization and decomposition of methyl linoleate hydroperoxides

In order to study antioxidant action on lipid hydroperoxide decomposition, the effects of alpha-tocopherol (TOH) and ascorbyl palmitate on the decomposition rate and reaction sequences of 9- and 13-cis,trans methyl linoleate hydroperoxide (cis,trans ML-OOH) decomposition in hexadecane were studied at 40 degrees C. Decomposition of cis,trans ML-OOH as well as the formation and isomeric configuration of methyl linoleate hydroxy and ketodiene compounds were followed by high-performance liquid chromatographic analysis. TOH effectively inhibited the decomposition of ML-OOH. The decomposition rate was two times slower at 0.2 mM and more than 10 times slower at 2 and 20 mM of TOH. Ascorbyl palmitate (0.2, 2, and 20 mM) slightly accelerated the decomposition of ML-OOH. Both compounds had an effect on the reaction sequences of ML-OOH decomposition. At high levels TOH inhibited the isomerization of cis,trans ML-OOH to trans,trans ML-OOH through peroxyl radicals and increased the formation of hydroxy compounds. Further, the majority of the hydroxy and ketodiene compounds formed had a cis,trans configuration, indicating that cis,trans ML-OOH decomposed through alkoxyl radicals without isomerization. These results suggest that when inhibiting the decomposition of hydroperoxides, TOH can act as a hydrogen atom donor to both peroxyl and alkoxyl radicals. In the presence of ascorbyl palmitate, cis,trans ML-OOH decomposed rapidly but without isomerization. In contrast to TOH, the majority of hydroxy compounds were cis,trans, but the ketodiene compounds were trans,trans isomers. This indicates that ascorbyl palmitate reduced cis,trans ML-OOH to the corresponding hydroxy compounds. However, the simultaneous formation of trans,trans ketodiene compounds suggests that ML-OOH decomposition, similar to the control sample, also occurred in these samples. Thus, under these experimental conditions, the reduction of ML-OOH to more stable hydroxy compounds did not occur to an extent significant enough to inhibit the radical chain reactions of ML-OOH decomposition.