Effects of α-, γ-, and δ-Tocopherols on Oxidative Stability of Soybean Oil

The effectts of 0, 100, 250, 500 and 1000 ppm of α-, γ-, or δ-tocopherol on oxidative stability of purified soybean oil in the dark at 55°C were studied. We measured peroxide value and headspace oxygen consumption in the samples. Purified soybean oil was prepared by liquid column chromatography. Tocopherols acted as antioxidants or prooxidants depending on their concentration. Optimum concentrations of α -, γ -, and δ– tocopherols to increase oxidative stability was 100, 250 and 500 ppm, respectively. The tocopherols had significant prooxidant effect (P < 0.05) at higher concentrations above this.     

Stability of α-, γ-, or δ-Tocopherol during Soybean Oil Oxidation

ABSTRACT:  The decomposition of α-, γ-, or δ-tocopherol in soybean oil during 24 d of storage at 50 °C was determined by high performance liquid chromatography (HPLC). The initial contents of α-, γ-, and δ-tocopherol in soybean oil were 53, 750, and 268 ppm, respectively. The degradation rates of α-, γ-, and δ-tocopherol for the first 10 d were 5.6%, 1.2, and 0.5% per day, respectively. The α-tocopherol was completely destroyed in 16 d. The destructions of γ- and δ-tocopherol were 28% and 17% after 24 d. The induction period of soybean oil determined by headspace oxygen, conjugated diene, and peroxide value was 8 d. As the degradations of α-, γ-, and δ-tocopherol increased, the headspace oxygen disappearance, conjugated diene formation, and peroxide value of soybean oil increased. The correlation coefficient between the degradation of tocopherols and the oxidation of soybean oil was about 0.95. The degradation of tocopherols in soybean oil during storage was due to the oxidation.     

Oxidative stability of Atlantic salmon (Salmo salar,L.) fillet enriched in α-, γ-, and δ-tocopherol through dietary supplementation

The purpose of this study was to examine the effect of dietary tocopherols on the oxidative stability of Atlantic salmon fillet. The fish were fed four diets supplemented with 150mg kg⁻¹ α-tocopherol and different combinations of γ- and δ-tocopherol (50 or 100mgkg⁻¹) for 10 months, slaughtered, and stored for 16 days on ice, or 48 weeks at −30 °C. Fillet concentrations of tocopherols at slaughter were 0.101 ± 0.001, 0.091 ± 0.004 and 0.025 ± 0.002 times feed concentration for α-, γ- and δ-tocopherol, respectively. Fillet α-tocopherol, but not γ- and δ-tocopherol, was moderately lowered during iced and frozen storage. The non-α-tocopherols protected the fillet against lipid oxidation in a dose-dependent manner during frozen storage, but appeared to act as prooxidants during storage on ice. It is concluded that α-tocopherol may be better suited than mixed tocopherols as a tool to optimize the oxidative stability of Atlantic salmon fillet.     

Loss of tocopherols and formation of degradation compounds in triacylglycerol model systems heated at high temperature

Triolein, trilinolein and a mixture of both (1:1) were heated at 180 °C for 2, 4, 6, 8 and 10 h in the absence of tocopherols or in the presence of α-tocopherol (500 mg kg⁻¹), δ-tocopherol (500 mg kg⁻¹) or a mixture of α-, β-, γ- and δ-tocopherol (200–250 mg kg⁻¹ each). Losses of tocopherols as well as increases in polymeric triacylglycerols were followed. Total polar compounds were also evaluated after 10 h heating. Results demonstrated that the antipolymerisation effect of tocopherols at high temperature depended on the degree of unsaturation affecting to a greater extent the less unsaturated substrate, triolein. The maximum effect for the three substrates was found when the tocopherol mixture was added. Interestingly, α-tocopherol losses were very rapid and independent of the unsaturation of the triacylglycerol system under the conditions used, although degradation of the substrate was significantly higher as the degree of unsaturation increased for any period of heating. © 1999 Society of Chemical Industry     

Effects of microwave energy on the relative stability of vitamin E in animal fats

The relative stabilities of individual tocopherols during microwave heating were evaluated in purified animal fats. Each tocopherol (α, β, γ and δ) was added to the purified beef tallow and lard at 0.25 μmol g^?1 fat immediately before use. During microwave heating the highest rate of loss was shown by α-tocopherol, followed by γ-, β- and δ-tocopherols. This order did not depend on the types of fats present. The indices such as peroxide value, carbonyl value and anisidine value for assessing quality of fats showed a significant difference (P < 0.05) in the final stage (12–20 min) of heating. It is therefore necessary that particular attention be paid to the loss of vitamin E when cooking pork or beef in a microwave oven.     

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.     

The effect of nitrogen fertilization on tocopherols in rapeseed genotypes

Tocopherols (α-, β-, γ- and δ-tocopherol) are naturally occuring antioxidants in vegetable oils. In rapeseed oil, α- and γ-tocopherols are the predominant isomers, while δ-tocopherol contributes much lower amounts to the total tocopherol content. Enhanced tocopherol content in seeds appears favourable, and breeding for tocopherol content has become an increasingly important objective in winter oilseed rape. The main objectives of this research were to quantify the amount of tocopherols in a number of rapeseed varieties and to investigate the effect of nitrogen fertilization on tocopherol concentration in the seed. The field trials were carried out in 2004–2005 and 2005–2006 at Dardanos, Çanakkale on the Turkish West Coast (10 km south of the city centre) with 13 varieties, three replications and three nitrogen levels (N₀: 0 kg/ha, N₁: 130 kg/ha and N₂: 260 kg/ha). The trial used a randomized complete block design with 6 m² plots. Tocopherol analysis was done using an HPLC system. Significant differences were found among the varieties and between the nitrogen levels. The average total tocopherol concentration was 118.7 mg kg^?1 for N₁, 134.1 mg kg^?1 for N₂ and 133.6 mg kg^?1 for N₃ fertilization level. MDS analysis indicated a rough grouping of line versus hybrid varieties and suggested that hybrids require more breeding effort to reach the level of tocopherols existed in line varieties.     

Effect of genotype and cultivation location on β-sitosterol and α-, β-, γ-, and δ-tocopherols in sorghum

This study aims to examine variations in β-sitosterol and α-, β-, γ-, and δ-tocopherol composition and content in sorghum grains with different genotypes and cultivation areas (Wonju and Miryang in Korea). β-Sitosterol content was found to be higher in Wonju sorghum; however, total tocopherol content was found to be higher in Miryang sorghum. Moreover, the β-sitosterol content did not correlate with physical characteristics, including 100-seed weight and color values (L, a, and b), but it was negatively correlated with total tocopherol content. β-Tocopherol was a major tocopherol in sorghum, constituting approximately 40%–46% of the total tocopherol content, and it was highly correlated with the total tocopherol content. Furthermore, the α-tocopherol content also increased with increasing γ-tocopherol content. Among the 4 tocopherols, only δ-tocopherol content correlated with physical characteristics of sorghum grain. This study deepened our knowledge of the variations in β-sitosterol and α-, β-, γ-, and δ-tocopherol content in sorghum with respect to genotype and cultivation location. In addition, this study demonstrated a correlation between some physical characteristics of sorghum and β-sitosterol/tocopherol content, and this information can be useful for breeding programs that develop or breed sorghum varieties or manufacture sorghum-based foods containing high amounts of β-sitosterol and tocopherols.     

KINETICS OF THE INTERACTION OF PANCREATIC α-AMYLASE WITH A KIDNEY BEAN (PHASEOLUS VULGARIS) - AMYLASE INHIBITOR

An amylase inhibitor isolated from black beans (Phaseolus vulgaris) can completely inhibit porcine pancreatic α-amylase forming a 1:1 stoichiometric complex. The kinetic pattern of complex formation is pH dependent. At pH 5.5 it follows a first order reaction with rate constant of 0.029 min^?1 and 0.017 min^?1 at 37°C and equimolar inhibitor and enzyme concentration, respectively, of 10^?8 M and 10^?9 M. At pH 6.9 it is a second order reaction, with a rate constant of 0.25 × 10⁶ M^?1 min^?1 at 37°C, with 4 × 10^?8 M concentrations of enzyme and inhibitor. The dissociation constants of the enzymeinhibitor complex are 1.7 × 10^?10 M at pH 5.5 and 4.4 × 10^?9 M at pH 6.9, at 37°C. The kinetic data obtained at pH 5.5 suggested the formation of an initial reversible complex followed by a conformational change step. The complex can be dissociated either in acid pH (4.3) or at pH values higher than 6, 5 with partial recovery of the amylase activity.     

Effects of catechin and α-tocopherol addition on the autoxidative stability of diacylglycerol oil derived from an olive oil and perilla oil mixture

The effects of tea catechin and α-tocopherol addition (1 mM) on the oxidative stability of oleic and linolenic acid-rich diacylglycerol (DAG) oil derived from an extra virgin olive oil and perilla oil mixture (6:4, w/w) were evaluated. Oil was oxidized at 50°C for 10 days, after which oxidation was evaluated based on headspace oxygen consumption and peroxide values (POV). The polyphenol and tocopherol contents were also monitored. Addition of catechin did not affect the oxygen consumption or POV of DAG oil, whereas α-tocopherol acted as a prooxidant. Addition of antioxidants had no significant (p>0.05) effect on the fatty acid composition of the oil. Degradation of γ-tocopherol during oil oxidation was inhibited by addition of α-tocopherol, and addition of antioxidants inhibited polyphenol degradation. The autoxidative stability of DAG oil can be improved using polar rather than non-polar antioxidants.     

Tocopherol Quantification by HPLC in Pecans and Relationship to Kernel Quality during Storage

Changes in tocopherols were followed in Stuart, Desirable and Schley cultivars during storage at 23.9°C and 60-70% RH and 0.6°C and 75% RH for 12 mo. Quality changes in the pecans were monitored using Hunter color measurements and conjugated diene measurement. α-, β-,γ- and 8-tocopherols were found in the three cultivars and γ-tocopherol was the primary form in each. Decreases of γ- and total tocopherols and L, hue angle and saturation index values were observed for pecans stored at 23.9°C (P < 0.05). Positive correlations (P < 0.05) were found between γ- and total tocopherols and Hunter color values for samples stored at 23.9°C. Conjugated diene levels did not correlate with tocopherol levels and Hunter values (P < 0.05). Pecans could be stored at 0.6°C and 75% RH for 12 mo without changes in kernel color, oil quality, tocopherols or conjugated diene levels.     

α-Tocopherol Content and Oxidative Stability of Egg Yolk as Related to Dietary α-Tocopherol

Hens fed diets with 0.0, 7.5, 15.0, 30.0, 60.0 and 120.0 mg supplemental α-tocopherol/kg feed produced egg yolks with 25,30,35,45,50 and 75 μg/g yolk, respectively. The correlation coefficient between dietary α-tocopherol (mg/kg diet) and egg yolk α-tocopherol (μg/g egg yolk) after 28 days feeding was 0.99. The supplemented dietary α-tocopherol had an effect on the α-tocopherol in egg yolk (p<0.05). The oxidative stability of yolk was determined by measuring the oxygen and volatile compounds in the headspace of bottled yolk. α-Tocopherol had an effect on the stability of yolk as an antioxidant at 25, 45 and 50 μg/g yolk and a prooxidant at 75 μg/g or above (p<0.05). The addition of 60.0 mg α-tocopherol/kg diet resulted in the best egg yolk stability. The correlation coefficient between headspace oxygen disappearance and volatile compound formation in the headspace of bottled egg yolk was 0.84.     

Influence of α-, γ-, and δ-tocopherol on the radiation induced formation of peroxides in rapeseed oil triacylglycerols

The effect of α-, γ-, and δ-tocopherols (enrichment: 1000 ppm) on the peroxide formation in rapeseed oil triacylglycerols (RSOTG) was evaluated. The oxidation process was initiated by gamma-irradiation with doses of 4 and 10 kGy. Whereas a pronounced antioxidant effect was observed for γ- and δ-tocopherol (sequence: δ- > γ-tocopherol), the inhibition extent of α-tocopherol was insignificant.     

High performance liquid chromatography method for the simultaneous determination of α-, γ- and δ-tocopherol in vegetable oils in presence of hexadecyltrimethylammonium bromide/n-propanol in mobile phase

A rapid methodology by RP-HPLC, 10 min of total analysis time, for the analysis of α-, γ- and δ-tocopherol in vegetable oils, in presence of retinol, retinyl acetate and α-tocopherol acetate was developed. Hexadecyltrimethylammonium bromide 0.1 M/n-propanol 65% (v/v) are used as mobile phase. Tocopherols were detected using UV and fluorescence detection. The quantification limits for α-, γ- and δ-tocopherols were 0.28, 0.12 and 0.23 mg L⁻¹, respectively. The method yielded satisfactory results when it was applied to vegetable oils and thus, it is suitable for their quality control.     

Effects and prooxidant mechanisms of oxidized alpha-tocopherol on the oxidative stability of soybean oil

ABSTRACT:  α-Tocopherol was oxidized in methanol containing methylene blue for 30 h under light. The effects of 0, 250, 500, 1000, and 1500 ppm of oxidized α-tocopherol on the oxidative stability of purified soybean oil in the dark at 55 °C were studied by measuring the peroxide values and headspace oxygen contents in sample bottles. As the concentrations of oxidized α-tocopherol increased, the peroxide values increased and the headspace oxygen contents decreased during the 6 d of storage. The oxidized α-tocopherol compounds acted as prooxidant on the peroxide values and headspace oxygen contents of purified soybean oil. Tukey's test showed that oxidized α-tocopherol had a significant effect on the peroxide value and headspace oxygen disappearance of oil at P < 0.05. The prooxidant mechanisms of oxidized α-tocopherol may be due to α-tocopherol peroxy radical, α-tocopherol oxy radical, hydroxy radical, and singlet oxygen formed from the α-tocopherol. The oxidized α-tocopherol containing polar and nonpolar groups in the same molecule may reduce the surface tension of oil to increase the transfer of headspace oxygen to oil and accelerate the oil oxidation.     

Prooxidant Activity of Oxidized α-Tocopherol in Vegetable Oils

ABSTRACT:  The effect of oxidized α-tocopherol on the oxidative stabilities of soybean, corn, safflower, and olive oils and the oxidation of oleic, linoleic, and linolenic acids were studied. The 0, 650, 1300, and 2600 ppm oxidized α-tocopherol were added to soybean, corn, safflower, and olive oils and 10000 ppm oxidized α-tocopherol to the mixture of oleic, linoleic, and linolenic acids. Samples in the gas-tight vials were stored in the dark for 6 or 35 d at 55 °C. The oxidative stabilities of oils were determined by headspace oxygen with GC and peroxide value. Fatty acids were determined by GC. As the concentration of oxidized α-tocopherol in soybean, corn, safflower, and olive oils increased, the depletion of headspace oxygen and the peroxide values of oils increased during storage. The prooxidant effects of oxidized α-tocopherol on soybean and corn oils with about 55% linoleic acid were greater than those on safflower and olive oils with about 12% linoleic acid, respectively ( P  < 0.05). The changes of fatty acids during storage showed that the oxidation ratios of oleic, linoleic, and linolenic acids were 1 : 2 : 3, 1 : 12 : 26, and 1 : 8 : 16 after 5, 30, and 35 d of storage, respectively. The oxidation of α-tocopherol in oil should be prevented and the oxidized α-tocopherol should be removed to improve the oxidative stability of oils.     

Characterization of Two α-Amylase Inhibitors from Black Bean (Phaseolus vulgaris)

Two inhibitors of α-amylase, I-1 and I-2, were purified from the black bean (Phaseolus vulgaris). The rate of complexation with porcine pancreatic α-amylase was very slow. I-l required 12 hr and I-2 6 hr for maximum inhibition at 30°C. The stoichiometry of complexation of α-amylase with I-1 was 2:1 and 1:1 with I-2. Optimum pH for complexation with I-1 ranged from 4.5 to 5.0 and 5.0 to 5.5 for I-2 and both were most stable at pH 3.0 to 4.0. An increase in ionic strength of the preincubation buffer from 0.106 to 0.906 enhanced the rate of inhibition 3 fold for both inhibitors. Maltose, a competitive inhibitor of α-amylase, added to the preincubation solution prevented complex formation for both inhibitors; however, it did not reverse the inhibition of the preformed complex. The dissociation constant for I-1 was 2.2 × 10^?9M and 3.8 × 10^?9M for I-2 at 30°C and pH 6.9. Both inhibitors functioned via a noncompetitive mechanism. I-2 was also stable at pH 2.0. I-2 was more stable to proteolytic digestion by trypsin than I-1 and was also stable to pepsin digestion.     

Physicochemical properties and oxidative stabilities of mealworm (<Emphasis Type="Italic">Tenebrio molitor</Emphasis>) oils under different roasting conditions

Physicochemical properties and oxidative stabilities of mealworm (Tenebrio molitor) oils under different roasting conditions were investigated. Oils were extracted using n-hexane from mealworms roasted at 200°C for 0, 5, 10, and 15 min and physicochemical properties and oxidative stabilities of oils were analyzed. Roasting increased the color intensity and the oleic acid and δ-tocopherol contents, but decreased linoleic acid, and α- and γ-tocopherol contents. An improvement in oxidative stability was observed in roasted mealworm oils, demonstrated by induction time and peroxide values. Mealworm oil contained abundant essential fatty acids and exhibited a superior oxidative stability.     

Kinetic Study of the Quenching Reaction of Singlet Oxygen by Common Synthetic Antioxidants (tert-Butylhydroxyanisol, tert-di-Butylhydroxytoluene, and tert-Butylhydroquinone) as Compared with α-Tocopherol

ABSTRACT: Effects of synthetic phenolic antioxidants (BHA, BHT, and TBHQ) on the methylene blue (MB) sensitized photooxidation of linoleic acid as compared with that of α‐tocopherol have been studied. Their antioxidative mechanism was studied by both ESR spectroscopy in a 2,2,6,6‐tetramethylpiperidone (TMPD)‐methylene blue (MB) system and spectroscopic analysis of rubrene oxidation induced by a chemical source of singlet oxygen. Total singlet oxygen quenching rate constants (k_ox?Q+k_q) were determined using a steady state kinetic equation. TBHQ showed the strongest protective activity against the MB sensitized photooxidation of linoleic acid, followed by BHA and BHT. TBHQ (1 × 10^?3 M) exhibited 86.5% and 71.4% inhibition of peroxide and conjugated diene formations, respectively, in linoleic acid photooxidation after 60‐min light illumination. The protective activity of TBHQ against the photosensitized oxidation of linoleic acid was almost comparable to that of α‐tocopherol. The data obtained from ESR and rubrene oxidation studies clearly showed the strong singlet oxygen quenching ability of TBHQ. The k_ox?Q+k_q of BHA, BHT, and TBHQ were determined to be 3.37 × 10⁷, 4.26 × 10⁶, and 1.67 × 10⁸ M^?1 s^?1, respectively. The k_ox?Q+k_q of TBHQ was within the same order of magnitude of that of α‐tocopherol, a known efficient singlet oxygen quencher. There was a high negative correlation (r² = ?0.991) between log (k_ox?Q+k_q) and reported oxidation potentials for the synthetic antioxidants, indicating their charge‐transfer mechanism for singlet oxygen quenching. This is the 1st report on the kinetic study on k_ox?Q+k_q of TBHQ in methanol as compared with other commonly used commercial synthetic antioxidants and α‐tocopherol.     

Fatty acids,tocopherols and proanthocyanidins in bramble seeds

Studies were conducted on the fatty acids, tocopherols and proanthocyanidins in the seeds of 10 bramble varieties from China. The oil yields from these seeds vary from 4.81% to 15.72%. The main fatty acids in bramble seed oils are C18:2 n-6 (51.0–66.1%), C18:3 n-3 (9.70–35.6%), C18:1 n-9 (9.85–16.3%), and C16:0 (2.01–5.73%). The major tocopherol in all seed oils of 10 varieties was γ-tocopherol. The composition (mg/100 g) was as follows: α-tocopherol 7.65–52.6, γ-tocopherol 46.9–106, δ-tocopherol 3.1–9.50, and the active vitamin E 15.9–61.5 among the varieties. The total proanthocyanidin content varies from 6.81 to 17.6 mg/g. The main oligomers in total proanthocyanidins are dimers, and the least are trimers. The contents and composite proportions of fatty acids, tocopherols and proanthocyanidins are different according the varieties, which should be taken into account when the bramble seeds are exploited.