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Results for “Oxidative stability”

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PubMed1999

Usefulness of the frequency data of the fourier transform infrared spectra to evaluate the degree of oxidation of edible oils.

The oxidation process of 13 edible oil samples with different proportions of oleic, linoleic, and linolenic acyl groups has been studied using Fourier transform infrared spectroscopy. The oxidation experiments were carried out by heating the samples in a convection oven at 70 degrees C. Duplicate spectra were recorded from a film of pure oil between two disks of KBr for each sample every day during the course of the oxidation, and frequency data of each band of the spectrum were collected automatically. Changes in the values of the frequency of most of the bands of the spectra were observed. The shiftings of the frequency value of specific bands allowed one to distinguish between the different stages of the oxidation process and to establish the oxidation degree of each oil sample. This methodology could be useful to evaluate the oxidative stability of edible oils in a simple, fast, and accurate way.

Oxidation-Reduction↗

PubMed2002

Temperature and pH dependence of the autoxidation rate of bovine, ovine, porcine, and cervine oxymyoglobin isolated from three different muscles--Longissimus dorsi, Gluteus medius, and Biceps femoris.

This study examined the temperature and pH dependence of the in vitro autoxidation rate of bovine, ovine, porcine, and cervine oxymyoglobin that had been isolated and purified from three muscles of different oxidative stability--Longissimus dorsi, Gluteus medius, and Biceps femoris. To avoid obtaining unreliable estimates of autoxidation rate as has occurred in many previous studies, in this study, precautions were taken to eliminate the effects of freezing, chemical reduction with hydrosulfite, and contaminating metal ions on the reaction rate. When these precautions were taken, the rate constants for the different myoglobins studied were similar to each other but were 2-7-fold lower, and the Ea (activation energy) was 20-100% higher than that reported in most previous studies. The type of muscle the myoglobin was isolated from had no effect on the reaction rate or the Ea; however, the species did have a significant effect (p < 0.05) with porcine myoglobin having a 10% lower reaction rate and a 20% lower Ea than myoglobin from the other species. Increasing the reaction pH from 5.50 to 6.50 produced an exponential increase in reaction rate but only a small curvilinear change in Ea that had a maximum at pH 6.00.

Animals↗

PubMedDate not supplied

Quantitative determination of loadings and oxidation products of polystyrene-bound phosphines using 31p MAS NMR.

The use of (31)P magic angle spinning (MAS) NMR for the quantitative determination of resin loadings and the building up of oxidation products was investigated. Loadings of polystyrene-bound phosphines were evaluated via addition of triphenyl phosphate as reference compound. Results for a series of phosphines are consistent with those obtained from well-established analytical methods. The compounds were also investigated with (13)C MAS NMR, and the individual oxidation stabilities were monitored under oxygen atmosphere.

Magnetic Resonance Spectroscopy↗

PubMed2005

Antioxidant activity of cysteine, tryptophan, and methionine residues in continuous phase beta-lactoglobulin in oil-in-water emulsions.

Proteins dispersed in the continuous phase of oil-in-water emulsions are capable of inhibiting lipid oxidation reactions. The antioxidant activity of these proteins is thought to encompass both free radical scavenging by amino acid residues and chelation of prooxidative transition metals; however, the precise mechanism by which this occurs remains unclear. In this study, the oxidative stability of cysteine, tryptophan, and methionine residues in continuous phase beta-lactoglobulin (beta-Lg) in a Brij-stabilized menhaden oil-in-water emulsion was determined. The presence of low concentrations of continuous phase beta-Lg (250 and 750 microg/mL) significantly inhibited lipid oxidation as determined by lipid hydroperoxides and thiobarbituric acid reactive substances analysis. It was observed that cysteine oxidized before tryptophan in beta-Lg, and both residues oxidized before lipid oxidation could be detected. No oxidation of the methionine residues of beta-Lg was observed despite its reported high oxidative susceptibility. It is conceivable that surface exposure of amino acid residues greatly affects their oxidation kinetics, which may explain why some residues are preferentially oxidized relative to others. Further elucidation of the mechanisms governing free radical scavenging of amino acids could lead to more effective applications of proteins as antioxidants within oil-in-water food emulsions.

Antioxidants↗

PubMed2004

Alpha-tocopherol-doped irradiated UHMWPE for high fatigue resistance and low wear.

Longevity of total joints has been compromised by wear and fatigue of ultrahigh molecular weight polyethylene (UHMWPE) components. Crosslinking reduces UHMWPE wear, but combined with postirradiation melting, also reduces its fatigue strength, therefore limiting its use in high-stress applications. We hypothesized that a lipophilic antioxidant (alpha-tocopherol, alpha-T) can protect UHMWPE against oxidation eliminating the need for postirradiation melting of crosslinked UHMWPE and improve its fatigue strength. To test these hypotheses, 65- and 100-kGy irradiated, alpha-T-doped and subsequently gamma-sterilized UHMWPE were used. (I) alpha-T-doped irradiated UHMWPEs showed significantly lower oxidation levels (0.48+/-0.25 and 0.44+/-0.06) compared to 100-kGy irradiated UHMWPE (3.74+/-0.16) after 5 weeks of accelerated aging at 80 degrees C in air. (II) Wear rate of alpha-T-doped irradiated UHMWPE (1.9+/-0.5, and 0.9+/-0.1mg/million cycles (MC) for 65- and 100-kGy irradiated UHMWPE, respectively) were comparable to that of 100-kGy irradiated/melted UHMWPE (1.1+/-0.7mg/million cycles). (III) The stress intensity factor at crack inception ( DeltaKi) of 100-kGy irradiated UHMWPE increased significantly upon doping with alpha-T from 0.74 to 0.87MPam(1/2) ( p<0.01 ). The DeltaKi for the 100-kGy irradiated and melted UHMWPE, currently in clinical use, was 0.55MPam(1/2). Doping with alpha-T eliminated the need for postirradiation melting to protect irradiated UHMWPE against long-term oxidation. The fatigue strength was improved by 58% for alpha-T-doped 100-kGy irradiated UHMWPE compared to irradiated and melted UHMWPE. The increase in oxidative stability of alpha-T-doped UHMWPE is attributed to the ability of alpha-T to react with peroxy free radicals on lipid chains and arrest the oxidation reactions. The improved fatigue strength is attributed to the increase in plasticity of UHMWPE due to the lipophilic nature of alpha-T.

Diffusion↗

PubMed2000

para-Substituted N-nitroso-N-oxybenzenamine ammonium salts: a new class of redox-sensitive nitric oxide releasing compounds.

N-Nitroso-N-oxybenzenamine ammonium salts with -OMe, -Me, -H, -F, -Cl, -CF3, and -SO2Me substituents at the para position of the phenyl ring constitute a new class of-redox sensitive nitric oxide (NO) releasing compounds. These compounds yield nitric oxide and the corresponding nitrosobenzene derivatives by a spontaneous dissociation mechanism after undergoing a one electron oxidation. Oxidation of these compounds can be achieved through chemical, electrochemical and enzymatic methods. It was observed electrochemically that the amount of NO generated was dependent on the substituent effect and the applied oxidation potential. Electron-withdrawing substituents increase the oxidation potential of the compound. A linear correlation was observed when the peak potentials for the oxidation were graphed versus the Hammett substituent constant. Density functional theory calculations were also performed on this series of compounds. The theoretical oxidation energies of the corresponding anions show a strong linear correlation with the experimental potentials. Furthermore, enzymatic oxidation using horseradish peroxidase showed a similar substituent effect. These results indicate that substitution at the para position of the phenyl ring has a profound effect on the stability, oxidation potential and enzymatic kinetic properties of the compounds. Thus para-substituted N-nitroso-N-oxybenzenamine salts comprise a new class of redox-sensitive nitric oxide releasing agents.

Electrochemistry↗

PubMed2004

Inhibition of lipid oxidation in pork bundles processing by superheated steam frying.

The effect of superheated steam treatment on the oxidative stability of lipids in packaged Zousoon (pork bundles) was investigated. The aroma quality of Zousoon samples was evaluated by sensory analysis and chromatographic analysis of volatiles. Results of this study indicated that oxidation of lipids occurred in pan-fried Zousoon after prolonged storage. Significant amounts of highly volatile compounds such as formaldehyde, acetaldehyde, acetone, and hexanal in Zousoon were identified by a modified method of cysteamine derivatization followed by gas chromatography-mass spectrometry (GC-MS) analysis. Superheated steam was found to be effective in suppressing lipid oxidation in canned Zousoon as compared with Zousoon fried by the conventional method in a frying pan. The superheated steam-fried samples had relatively low thiobarbituric acid reactive substance (TBARS) and peroxide (POV) values before and after storage, whereas samples prepared by pan frying had relatively high TBARS and POV values before and after storage. Superheated steam-fried Zousoon had superior lipid stability to that prepared by the conventional pan-frying method.

Aldehydes↗

PubMed2001

Antioxidant properties of evening primrose seed extracts.

The antioxidant activity of extracts of evening primrose seeds (SE) and a commercially extracted filter cake (FC) were determined. The SE and FC were extracted with methanol/water (9:1) followed by evaporation and concentration. Extracts were tested in a bulk oil system and an oil-in-water emulsion using safflower oil as the major source of lipids. The antioxidant activity of the extracts was compared to that of a control and to that of butylated hydroxytoluene (BHT), singly, and in combination. Antioxidant activity was measured by the co-oxidation of beta-carotene, an oxidative stability instrument, conjugated dienes, and headspace analysis of hexanal. The SE extract had greater antioxidant activity than the FC extract. The SE extract was more effective in controlling the oxidation in the oil-in-water model system than in the bulk oil system. The activity of SE was concentration dependent, and at higher concentrations the SE was as effective as BHT, but it required higher concentrations because of its lack of purity. Synergism between SE and BHT was demonstrated in both model systems.

Antioxidants↗

PubMed2002

Effect of high-oleic trait and paste storage variables on sensory attribute stability of roasted peanuts.

There has been much interest in the effect of the high-oleic acid trait of peanuts on various quality factors since discovery of high levels of oleic acid in a peanut mutant genotype. The trait provides greater oxidative stability for the high-oleic oil and seed. Several research groups have investigated high-oleic peanut oil and roasted peanut flavor characteristics, which were similar within high-oleic lines compared to Florunner. It was observed that some high-oleic lines derived from the Sunrunner cultivar have consistently higher predicted breeding values for roasted peanut attribute than Sunrunner itself. This study investigated if this apparent effect of the trait was an artifact arising from the handling procedures during processing and storage or from flavor fade. High-oleic lines used were derived by backcrossing the trait into existing cultivars, and the comparison of sensory attribute intensity was with the recurrent parent used in backcrossing. Previous comparisons have been between lines differing in more than just oleate content, that is, with widely different background genotypes that could contribute to the differences observed. Differential rates of change in sensory attributes were found in different background genotypes, suggesting that the comparison of high- and normal-oleic lines should be made in common background genotypes as well as in common production and postharvest environments. There was no measurable change in roasted peanut attribute in samples stored at -20 degrees C over the 63 day duration of this experiment. There were changes in roasted peanut in samples stored at 22 degrees C, confirming that storage at -20 degrees C is sufficient for large studies that require multiple sensory panel sessions over a period of weeks.

Arachis↗

PubMed2002

Suppressive effect of saturated acyl L-ascorbate on the oxidation of linoleic acid encapsulated with maltodextrin or gum arabic by spray-drying.

6-O-Palmitoyl L-ascorbate was added to linoleic acid at various molar ratios of the ascorbate to the acid, the mixtures were emulsified with a maltodextrin or gum arabic solution, and the emulsions were spray-dried to produce microcapsules. At higher molar ratios, the oil droplets in the emulsions were smaller, and the oxidative stabilities of the encapsulated linoleic acid were higher for both the maltodextrin- and gum arabic-based microcapsules. 6-O-Capryloyl, caproyl, and lauroyl L-ascorbates, which were synthesized through lipase-catalyzed condensation in acetone, were also used for the microencapsulation of linoleic acid. Except for capryloyl L-ascorbate, the addition of a saturated acyl ascorbate, especially caproyl ascorbate, to linoleic acid was effective for preparing oil droplets of small particle diameter and for suppressing the oxidation of the encapsulated linoleic acid.

Acylation↗

PubMed2000

Directed evolution of microbial oxidative enzymes.

In the past year, a number of oxidative enzymes have been the target of directed evolution. Catalase reaction specificity has been shifted to peroxidase, the high pH, thermal and oxidative stability of a fungal peroxidase has been dramatically improved, and the substrate specificity of cytochrome P450 has been altered to include substrates that the wild-type enzymes are incapable of oxidizing.

Biotechnology↗

PubMed1993

Protein engineering of subtilisins to improve stability in detergent formulations.

Microbial proteases are used extensively in a large number of industrial processes and most importantly in detergent formulations facilitating the removal of proteinaceous stains. Site-directed mutagenesis has been employed in the construction of subtilisin variants with improved storage and oxidation stabilities. It is shown that in spite of significant structural homology between subtilisins subjected to protein engineering the effects of specific mutations can be quite different. Mutations that stabilize one subtilisin may destabilize another.

Amino Acid Sequence↗

PubMed2004

Antioxidative effects of glycosyl-ascorbic acids synthesized by maltogenic amylase to reduce lipid oxidation and volatiles production in cooked chicken meat.

Glycosylated ascorbic acids were synthesized by using the transglycosylation activity of Bacillus stearothermophilus maltogenic amylase with maltotriose to show effective antioxidative activity with enhanced oxidative stability. The modified ascorbic acids comprised mono- and di-glycosyl transfer products with an alpha-(1,6)-glycosidic linkage. The antioxidative effects of the glycosyl derivatives of ascorbic acid on the lipid oxidation of cooked chicken breast meat patties were compared, and the synergistic effect when combined with alpha-tocopherol was determined in terms of thiobarbituric acid-reactive substances (TBARS) and volatiles production during storage. The results indicate that the glycosylated ascorbic acids had very effective antioxidative activity in preventing lipid oxidation, and were better in their synergistic effect in comparison to authentic ascorbic acid, with maltosyl-ascorbic acid being the most effective. Volatiles production was highly correlated with the TBARS values in the lipid oxidation of cooked meat. The antioxidative effect preventing the production of volatiles was particularly strong on pentanal, fairly strong on propanal and butanal, and not at all on ethanal. Propanal, pentanal, and the total volatiles thus provided a good representation of the lipid oxidation status of cooked chicken meat.

Aldehydes↗

PubMed2002

Production in large quantities of highly purified hydroxytyrosol from liquid-solid waste of two-phase olive oil processing or "Alperujo".

The effect of hydrothermal treatment of two-phase olive waste (alperujo) on the solubilization of hydroxytyrosol was studied. Different conditions of saturated steam were assayed. A high amount of hydroxytyrosol was solubilized and increased with increasing steaming temperature and time, reaching 1.4-1.7 g/100 g of dry alperujo. The effect of acidic (H(2)SO(4)) and basic (NaOH) catalysts was also evaluated. Acid-catalyzed treatment was more effective at milder conditions, whereas the alkali-catalyzed conditions were not very suitable. In the present study, the extracted hydroxytyrosol was purified by means of a new, simple, and inexpensive chromatographic system, under international patent application (PCT/ES02/00058). From 1000 kg of alperujo, with 70% humidity, can be obtained approximately 4.5-5 kg of hydroxytyrosol. After a purification process, at least 3 kg of hydroxytyrosol, at 90-95% purity, would be obtained. The purified compound was identified by HPLC/UV and (1)H and (13)C NMR analyses, and its antioxidant activity was tested on refined olive oil without antioxidants by Rancimat method. The oxidative stability of refined olive oil was increased by a factor of 1.71 in the presence of 100 ppm of hydroxytyrosol.

Chromatography, High Pressure Liquid↗

PubMed1999

Oxidative resistance of Na/K-ATPase.

1. Oxidative modification of Na/K-ATPase from brain and kidney has been studied. Brain enzyme has been found to be more sensitive than kidney enzyme to inhibition by both H2O2 and NaOCl. 2. The inhibition of Na/K-ATPase correlates well with the decrease in a number of SH groups, suggesting that the latter belong mainly to ATPase protein and are essential for the enzyme activity. We suggest that the differences in the number, location, and accessibility of SH groups in Na/K-ATPase isozymes predict their oxidative stability. 3. The hydrophilic natural antioxidant carnosine, the hydrophobic natural antioxidant alpha-tocopherol, and the synthetic antioxidant ionol as well as the ferrous ion chelating agent deferoxamine were found to protect Na/K-ATPase from oxidation by different concentrations of H2O2. The data suggest that these antioxidants are effective due to their ability to neutralize or to prevent formation of hydroxyl radicals.

Animals↗

PubMed1998

Effects of processing steps on the contents of minor compounds and oxidation of soybean oil.

The effects of minor compounds on the oxidative stability of soybean oil were studied by measuring the contents of peroxides, headspace oxygen and volatile compounds. The effects of processing on minor component contents were also studied. Fatty acids, mono- and diacylglycerols, thermal or oxidized triacylglycerols, oxidized tocopherols and peroxides acted as prooxidant in soybean oil during storage at 55 degrees C. The phospholipids acted as prooxidant or antioxidant depending on the presence or absence of metals in the oil. The tocopherols acted as prooxidant or antioxidant depending on their concentration in the oil. The chlorophyll acted as a sensitizer to generate singlet oxygen in the photooxidation of soybean oils.

Antioxidants↗

PubMed2001

Oxidation of ascorbate in raw milk induced by enzymes and transition metals.

The effect of xanthine oxidase, lactoperoxidase, and transition metals [Fe(III), Cu(II)] on the oxidation of ascorbate in raw milk was investigated. Data clearly showed that iron(III) (200 microM) does not accelerate ascorbate oxidation in raw milk in concentrations relevant for raw milk. In contrast, addition of copper(II) (10 microM) to the raw milk accelerated oxidation of ascorbate. Furthermore, both xanthine oxidase and peroxidase activity were found to accelerate ascorbate oxidation dramatically in raw milk, indicating that xanthine oxidase and lactoperoxidase might be some of the most obvious candidates for mediation of ascorbate oxidation in raw milk. The present data are discussed in relation to using the fate of ascorbate in raw milk as an indicator of the oxidative stability of the milk.

Animals↗

PubMed2006

Dose and duration effect of alpha-tocopheryl acetate supplementation on chicken meat fatty acid composition, tocopherol content, and oxidative status.

The effects of dietary alpha-tocopheryl acetate (alpha-TA) doses (75, 150, and 225 mg/kg) and the duration of this supplementation (0, 10, 21, 32, and 43 days prior to slaughter) on fatty acid composition, alpha-tocopherol content, and oxidative status were studied either in raw or in cooked dark chicken meat with its skin. With regard to fatty acid composition, raw meat was affected by both dietary factors. Various polyunsaturated fatty acids decreased as a result of higher alpha-TA doses, whereas these fatty acids increased with longer supplementation periods. Cooked meat showed similar trends for the duration of alpha-TA supplementation. On the other hand, alpha-tocopherol content in raw and cooked meat increased as a result of the dose and duration of alpha-TA supplementation. Formation of lipid hydroperoxides and thiobarbituric acid values of these meats were also influenced by these two dietary factors, and the dietary combination of 150 mg/kg of alpha-TA during the last 32 days was optimal in terms of supplementation costs and meat oxidative stability.

Animals↗