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Results for “Oxidative stability”

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At least 235 records · Page 13Linked to original sources

PubMed2005

Effects of different levels of dietary supplemental selenium on performance, lipid oxidation, and color stability of broiler chicks.

This study examined the effects of supplemental dietary selenium on growth performance, lipid oxidation, and color stability of broiler chicks. Male broiler chicks (Arbor Acres, 1 d old, total 900 chicks) were randomly assigned to 6 pens containing 30 chicks each, corresponding to each of 6 dietary treatments. Six different diets were supplied to the chicks from 3 to 6 wk of age. After 42 d of feeding, all the broilers were slaughtered conventionally at a slaughtering plant. The carcasses were packed in polyethylene bags in a manner similar to that used for retail trade and stored for 12 d at 4 degrees C. Body weight and feed efficiency were not affected by dietary selenium levels, and no adverse effect on growth was observed during the experimental period. The dietary selenium and alpha-tocopherol levels did not affect surface meat color or level of metmyoglobin accumulation. Lipid stability was improved by supplementation with 100 IU of alpha-tocopherol (P < 0.05). Dietary selenium supplementation at 8 ppm in combination with 100 IU of alpha-tocopherol, however, was more effective in reducing lipid oxidation compared with 100 IU of alpha-tocopherol/kg feed only (P < 0.05). Supplementation with 100 IU of alpha-tocopherol affected cholesterol oxidation product levels on d 7 and 12, but selenium supplementation did not have an additional effect on the reduction of cholesterol oxidation products. Therefore, an increase in the dietary selenium from 1 to 8 ppm revealed only minor improvements in the oxidative stability of chicken meat during refrigerated storage.

Animals↗

PubMed2002

Stability of virgin olive oil. 1. Autoxidation studies.

Virgin olive oil samples with similar oxidative stabilities and fatty acid compositions were stored for 24 months. Changes in the lipid substrate were followed by peroxide value and K(232) measurements. HPLC was used to evaluate changes in the alpha-tocopherol, pigment, and squalene contents. Total polar phenol content was measured colorimetrically. The loss of alpha-tocopherol and carotenoids was comparable with that of polar phenol content, suggesting an active participation in autoxidation. The limited role of squalene in autoxidation was further confirmed using an olive oil model and in the presence of alpha-tocopherol. Pheophytin a degradation was high, although spectrometric estimation of chlorophyll content did not indicate so. Evaluation of pheophytin a activity at three different levels of addition on the oil model indicated a concentration-dependent antioxidant role more pronounced at elevated temperatures, which could be partially due to the activity of certain degradation products.

Carotenoids↗

PubMed2005

Electron spin resonance spin trapping for analysis of lipid oxidation in oils: inhibiting effect of the spin trap alpha-phenyl-N-tert-butylnitrone on lipid oxidation.

The electron spin resonance (ESR) spin trapping technique was investigated as an analytical approach to follow lipid oxidation of rapeseed oil, sunflower oil, and fish oil during storage at 40 degrees C. Unlike previous investigations, alpha-phenyl-N-tert-butylnitrone (PBN), used as spin trap, was added to the fresh oils and formation of radicals was monitored during storage. Results were compared with the development in peroxide value (PV) and the thiobarbituric acid index (TBA). Increasing radical development was detected during the initial stages of oxidation, during which no significant changes in PV and TBA were observed. Evidence of spin adduct depletion was found during prolonged storage, suggesting that although spin trapping of radicals may be used to follow early events in lipid oxidation, it is not a suitable parameter for long periods of time. Addition of the spin trap after sequential samplings is recommended for getting an insight of oxidative changes during storage. Further, the influence of the spin trap (PBN) on lipid oxidation was studied in detail by application of PV and TBA and by following the depletion of naturally occurring tocopherol. PBN was found to possess a profound inhibiting effect on lipid oxidation. Such an effect was found to be dependent on the nature of the oil, and it was observed that the lower the oxidative stability, the larger the effect of PBN on lipid oxidation. This effect was interpreted in terms of the capability of PBN to react with peroxyl radicals, which in turn depends on the initial tocopherol content of the oils.

Cyclic N-Oxides↗

PubMed2005

Reinforcing effect of organo-modified layered silicates in high-density polyethylene.

This study focuses on the understanding of the reinforcing effect given by organo-modified layered silicates to a high-density polyethylene and the influence on the crystallization properties of this polymer. The addition of organo-modified clay to high-density polyethylene resulted in an evident increase in the tensile and flexural Young's modulus of the material with respect to unfilled polymer. The morphology, crystallinity, and thermo-oxidative stability of such nanocomposites were investigated using X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, and oxidation induction time test. The materials obtained show tactoid as well as intercalated and exfoliated structures with different dominant states depending on the loading level and process conditions. It was observed that organic ions not only change mixing behavior but also influence material properties, including the degree of crystallinity and the stability to the thermo-oxidative phenomena.

Aluminum Silicates↗

PubMed2006

Nitric oxide decreases the stability of DMPO spin adducts.

The effect nitric oxide (NO*) on the stability of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) adducts has been investigated using EPR spectroscopy. We report that the DMPO/HO* adduct, generated by porcine pulmonary artery endothelial cells in the presence of H2O2 and DMPO, or by a Fenton system (Fe(II)+H2O2) is degraded in the presence of the NO*-donor, 2-(N,N-diethylamino)-diazenolate-2-oxide (DEANO) or by bolus addition of an aqueous solution of NO*. A similar effect of DEANO was observed on other DMPO adducts, such as DMPO/*CH3 and DMPO/*CH(CH3)OH, generated in cell-free systems. Measurements of the loss of DMPO/HO* in the presence of DEANO in aerated and oxygen-free buffers showed that in both of these settings the process obeys first-order kinetics and proceeds with similar efficacy. This indicates that direct interaction of the nitroxide with NO*, rather than with NO2* (formed from NO* and O2 in aerated media), is responsible for destruction of the spin adduct. These results suggest that the presence of NO* may substantially affect the quantitative determination of DMPO adducts. We also show that NO2* radicals, generated by a myeloperoxidase/H2O2/nitrite system, also degrade DMPO/HO*. Because DMPO is frequently used to study generation of superoxide and hydroxyl radicals in biological systems, these observations indicate that extra caution is required when studying generation of these species in the presence of NO* or NO2* radicals.

Animals↗

PubMed1998

Effect of mutations in Candida antarctica B lipase.

Three variants of the Candida antarctica B lipase have been constructed and characterized. The variant containing the T103G mutation, which introduces the consensus sequence G-X-S-X-G found in most other known lipases, shows an increased thermostability but retains only half the specific activity of the native enzyme. Also in ester synthesis the activity is lowered but the specificity and enantioselectivity remains unchanged. The W104H mutant, in which more space is introduced into the active site, has more dramatically changed properties. Both the thermostability and the specific activity are slightly reduced but the activity and specificity in ester synthesis is highly different from the native enzyme. In general, the activity is very low and the enantioselectivity is, furthermore, highly reduced. Finally, the mutation M72L was introduced to increase the oxidation stability of the enzyme. This variant did exhibit an increased resistance towards oxidation but the thermostability was, unfortunately, also reduced.

Candida↗

PubMed2005

Effects of protein and peptide addition on lipid oxidation in powder model system.

The effect of protein and peptide addition on the oxidation of eicosapentaenoic acid ethyl ester (EPE) encapsulated by maltodextrin (MD) was investigated. The encapsulated lipid (powder lipid) was prepared in two steps, i.e., mixing of EPE with MD solutions (+/- protein and peptides) to produce emulsions and freeze-drying of the resultant emulsions. EPE oxidation in MD powder progressed more rapidly in the humid state [relative humidity (RH) = 70%] than in the dry state (RH = 10%). The addition of soy protein, soy peptide, and gelatin peptides improved the oxidation stability of EPE encapsulated by MD, and the inhibition of lipid oxidation by the protein and the peptides was more dramatic in the humid state. Especially, the oxidation of EPE was almost perfectly suppressed when the lipid was encapsulated with MD + soy peptide during storage in the humid state for 7 days. Several physical properties such as the lipid particle size of the emulsions, the fraction of nonencapsulated lipids, scanning electron microscopy images of powder lipids, and the mobility of the MD matrix were investigated to find the modification of encapsulation behavior by the addition of the protein and peptides, but no significant change was observed. On the other hand, the protein and peptides exhibited a strong radical scavenging activity in the powder systems as well as in the solution systems. These results suggest that a chemical mechanism such as radical scavenging ability plays an important role in the suppression of EPE oxidation in MD powder by soy proteins, soy peptides, and gelatin peptides.

Capsules↗

PubMed2005

Effects of the addition of amino acids and peptides on lipid oxidation in a powdery model system.

The effects of the addition of amino acids and peptides on the oxidation of eicosapentaenoic acid ethyl ester (EPE) encapsulated by maltodextrin (MD) were investigated. The encapsulated lipid was prepared in two steps, that is, by mixing of EPE with MD solutions (+/-amino acids and peptides) to produce emulsions and freeze-drying of the resultant emulsions. The addition of amino acids and peptides improved the oxidation stability of EPE encapsulated with MD, and the inhibition of lipid oxidation by the amino acids and peptides was more effective at 70% relative humidity (RH). Met, Arg, and Trp were effective amino acids for antioxidation at RH = 10 and 40%, whereas at RH = 70%, His was the most effective amino acid, preventing the oxidation of EPE almost perfectly. Carnosine also exhibited a strong antioxidant effect at RH = 70%, but the effect of anserine was inferior. The addition of Met + Trp or Met + Arg inhibited the oxidation of EPE encapsulated with MD at RH = 40%. Cys accelerated the oxidation of EPE, indicating that the thiyl radical may act as a pro-oxidant. No close relationship was observed between the radical scavenging abilities of amino acids and peptides measured in the aqueous diphenylpicrylhydrazyl solution and their antioxidative effects in the powdery system. It is possible that the radical-scavenging ability of amino acids and peptides detected by ESR in the powder system is responsible for the antioxidative activity of these compounds.

Amino Acids↗

PubMed2004

Inactivation of Bacillus stearothermophilus leucine aminopeptidase II by hydrogen peroxide and site-directed mutagenesis of methionine residues on the enzyme.

Leucine aminopeptidases (LAPs) are exopeptidases that remove the N-terminal L-leucine from peptide substrates. Oxidative stability assay showed that the recombinant Bacillus stearothermophilus LAP II (rLAPII) was sensitive to oxidative damage by hydrogen peroxide at the elevated temperature. The H2O2-treated enzyme experienced obvious changes in the secondary structure when the oxidant concentration increased to 300 mM. To investigate the role of methionine residues on the oxidative inactivation, each of the five methionine residues in the rLAPII was replaced with leucine by site-directed mutagenesis. The mutant enzymes with an apparent Mr of approximately 44.5 kDa were overexpressed in Escherichia coli and were purified to homogeneity by nickel-chelate chromatography. The specific activities for Met82Leu, Met88Leu, Met254Leu, and Met382Leu were similar to that of the wild-type enzyme, whereas a reduced activity was observed in Met136Leu. The 50% decrease in the catalytic efficiency (kcat/Km) for Met136Leu was caused by 47% decrease in kcat value. As compared with the wild-type enzyme, all mutant proteins were more sensitive to the oxidant, implying that the methionine residues of B. stearothermophilus LAP II are important for the protection of the enzyme from oxidative inactivation.

Amino Acid Substitution↗

PubMed2002

Antioxidant properties of differently processed spinach products.

The effect of variously processed spinach products (whole-leaf, minced and enzymatically liquefied spinach) on lipid oxidation was determined. In an autoxidative methyl linoleate (MeLo) system the inhibition of hydroperoxide formation, measured by HPLC after three days of oxidation, was in descending order: whole-leaf > liquefied > minced spinach. The inhibition of formation of thiobarbituric acid-reactive substances (TBARS) and hexanal by spinach was determined in cooked meatballs with added spinach after two days of storage at 4 degrees C. The formation of TBARS was inhibited by liquefied spinach at 200 g/kg meat; all other spinach products tested at 100 and 200 g/kg were pro-oxidative. The formation of hexanal was inhibited by both minced and liquefied spinach at 100 and 200 g/kg meat. The variously processed spinach products behaved differently when tested for their antioxidant activity (MeLo) or oxidative stability (meatballs). We conclude that the effect of spinach products on lipid oxidation is affected by processing.

Aldehydes↗

PubMed2005

Pharmacologic manipulation of the ataxia-telangiectasia mutated gene product as an intervention in age-related disease.

Ataxia-telangiectasia (A-T) is an autosomal recessive disorder characterized by progressive ataxia, elevated cancer incidence, and premature aging. A-T cells, Atm-deficient mice, and individuals with A-T show increased oxidant sensitivity, genomic instability, altered IGF-1 and p53 signaling, and rapid telomere shortening compared to normal controls. The gene mutated in A-T, ATM, regulates DNA repair, IGF-1 and p53 signaling, age pigment removal, antioxidant capacity, and telomere maintenance - pathways involved in and often attenuated with aging. Interestingly, flavonoids with chemopreventative effects, such as quercetin, genistein, and epigallocatechin gallate activate ATM. Since ATM activates pathways which increase genomic stability, oxidant resistance, and/or telomere stability, and since many diseases of old age (i.e., cancer, cardiovascular and neurodegenerative disease), result from attenuation of these pathways, pharmacologic manipulation of ATM activity via flavonoid intake may prove useful in slowing the appearance of age-associated disease.

Aging↗

PubMed2002

Ability of surfactant micelles to alter the partitioning of phenolic antioxidants in oil-in-water emulsions.

In oil-in-water emulsions, the physical location of antioxidants can be an important determinant in their activity. Surfactants can potentially influence the physical location of antioxidants in oil-in-water emulsions by causing solubilization of lipid-soluble antioxidants into the aqueous phase. Excess Brij micelles in an oil-in-water emulsion were found to increase the partitioning of phenolics into the continuous phase with polar antioxidants (propyl gallate) partitioning more than nonpolar antioxidants (butylated hydroxyltoluene). Solubilization of propyl gallate was rapid coming to equilibrium in less than 5 min. Increasing surfactant micelle concentrations from 0.3 to 2.8% increased the solubilization of propyl gallate by 2.3-fold. Solubilization of phenolic antioxidants into the aqueous phase by Brij micelles did not alter the oxidative stability of salmon oil-in-water emulsions, suggesting that surfactant micelles influenced oxidation rates by mechanisms other than antioxidant solubilization.

Alkanes↗

PubMed2006

Nitric oxide modifies the sarcoplasmic reticular calcium release channel in endotoxemia by both guanosine-3',5' (cyclic) phosphate-dependent and independent pathways.

OBJECTIVES: a) To determine whether decreased sarcoplasmic calcium release channel (CRC) activity is a mechanism by which myocardial contractility is reduced in endotoxemia; b) to determine whether nitric oxide modulates CRC activity in endotoxemia; and c) to examine two nitric oxide signaling pathways in relation to CRC function in endotoxemia. DESIGN: Randomized, prospective using a rat model of endotoxemia. SETTING: : Research laboratory. SUBJECTS: Sprague-Dawley rats. INTERVENTIONS: Endotoxemia was induced by lipopolysaccharide administration. The effects of nitric oxide were studied using the highly selective inducible nitric oxide synthase inhibitor N-(3-(aminomethyl)benzyl)acetamidine dihydrochloride (1400W) and the specific guanylyl cyclase inhibitor 1-H (1, 2, 4)oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). MEASUREMENTS AND MAIN RESULTS: We assessed myocardial contractility, myocardial nitric oxide content, and guanosine-3',5' (cyclic) phosphate (cGMP) content. We determined CRC activity by calcium release and ryanodine binding assays. We followed these variables at four time points through the course of endotoxemia. We found that myocardial contractility and CRC activity were decreased in late but not in early endotoxemia. Furthermore, inducible nitric oxide synthase inhibition with 1400W restored contractility and CRC activity in late endotoxemia but paradoxically worsened these variables in early endotoxemia. Through the use of the guanylyl cyclase inhibitor ODQ, we demonstrate that nitric oxide acts through cGMP-mediated mechanisms in early and late endotoxemia. We investigated cGMP-independent pathways by assessing the oxidative status of the CRC. We found that in late endotoxemia, nitric oxide decreased the number of free thiols, demonstrating that nitric oxide also acts through cGMP-independent pathways. CONCLUSIONS: Nitric oxide has a dual effect on the CRC in endotoxemia. At low concentrations, as measured in early endotoxemia, nitric oxide stabilizes the CRC through cGMP-mediated mechanisms. In late endotoxemia, high nitric oxide concentrations decrease channel activity through both cGMP-dependent and cGMP-independent mechanisms.

Animals↗

PubMed1991

Redox derivatives of tranylcypromine: syntheses, properties, and monoamine oxidase inhibitor activity of some chemical delivery systems.

Several brain-targeting chemical delivery systems (CDS) based on a dihydropyridine----pyridinium salt type redox system were synthesized for the monoamine oxidase (MAO) inhibitor tranylcypromine (TCP). The dihydronicotinate moiety was chemically attached to the amino group of TCP by either an amide or substituted carbamate linkages. Physicochemical studies of the new derivatives, including chromatographic Rm determinations, were performed. Only the substituted carbamate-type derivatives manifested an increased lipophilicity relative to the parent compound. In vitro oxidation stability studies were also performed on selected derivatives using a ferricyanide-mediated method. Results of this assay showed that the dihydropyridine-type derivatives oxidized to the respective quaternary salt forms with stabilities which empirically correlated with other effective CDSs. Preliminary in vivo studies performed in rats indicated that some of the new derivatives exerted significant biological activity.

Animals↗

PubMed1998

Glyceryl monooleate cubic phase gel as chemical stability enhancer of cefazolin and cefuroxime.

The primary objective of this study was to determine the ability of the glyceryl monooleate (GMO) cubic phase gel to protect drugs from chemical instability reactions such as hydrolysis and oxidation. Stability was assessed on cefazolin incorporated in cubic phase gel and in solution at two different concentrations (200 and 50 micrograms/g), at 22, 37, and 50 degrees C. Degradation profiles, plotting percent cefazolin remaining on a logarithmic scale versus time, were constructed and the degradation rate constants calculated from the slopes. At both concentrations, degradation of cefazolin was found to be slower in the cubic phase gel than in solution at 22 and 37 degrees C, but not at 50 degrees C. The degradation rate constants were 3- to 18-fold lower in the gel than in solution at low concentration of cefazolin. At 22 and 37 degrees C, the kinetics of degradation at high concentration of cefazolin was not first-order but showed a lag phase followed by an exponential loss of cefazolin, typical of oxidation. The potential oxidation of the thioether moiety of cefazolin was confirmed by its 18-fold higher stability in the presence of ethylenediaminetetraacetic acid (EDTA) and nitrogen in solution. Cefuroxime, a cephalosporin which degrades solely via beta-lactam hydrolysis, degraded twice as fast in solution as it did in the gel. The enhanced stability of cefazolin and cefuroxime in the GMO cubic phase gel shows its potential as a chemical stability enhancer and this is the first report to demonstrate oxidation, in addition to beta-lactam hydrolysis, as a mechanism for degradation of cefazolin.

Cefazolin↗

PubMed2004

Effects of sterol structure, temperature, and lipid medium on phytosterol oxidation.

Factors contributing to the oxidative stability of phytosterols were studied. Unsaturated stigmasterol and saturated sitostanol were used as model compounds and were heated at different temperatures in different lipid matrices for various periods of time. Accumulations of the major secondary oxidation products were used as a marker of the stability of heated compounds, and the products were analyzed by gas chromatography-mass spectrometry. The results showed that both temperature and heating time, as well as sterol structure and lipid matrix composition, affected phytosterol oxidation. In particular, the interactions between different lipid matrices and temperatures had drastic effects on the total contents of the phytosterol oxides formed and also on the reaction pathways of oxidation. During heating at high temperatures for prolonged periods, >20% of stigmasterol was oxidized. At moderate temperatures the oxidation of stigmasterol was rather slow. Sitostanol oxide contents were low under all heating conditions studied.

Drug Stability↗

PubMed2002

Effect of emulsifier on oxidation properties of fish oil-based structured lipid emulsions.

The effects of the emulsifiers lecithin, Tween 20, whey protein isolate, mono-/diacylglycerols, and sucrose fatty acid ester on oxidation stability of a model oil-in-water emulsion prepared with enzymatically synthesized menhaden oil-caprylic acid structured lipid were evaluated. Oxidation was monitored by measuring lipid hydroperoxides, thiobarbituric acid reactive substances, and the ratio of combined docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) contents to palmitic acid in the emulsion. After high-pressure homogenization, all emulsions, except those prepared with lecithin, had similar droplet size distributions. All structured lipid emulsions, except for the lecithin-stabilized emulsions, were stable to creaming over the 48-day period studied. Emulsifier type and concentration affected oxidation rate, with 0.25% emulsifier concentration generally having a higher oxidation rate than 1% emulsifier concentration. Overall, oxidation did not progress significantly enough in 48 days of storage to affect DHA and EPA levels in the emulsion.

Diglycerides↗

PubMed2004

Effect of soft-segment chemistry on polyurethane biostability during in vitro fatigue loading.

The effect of soft-segment chemistry on biostability of polyurethane elastomers was studied with a diaphragm-type film specimen under conditions of static and dynamic loading. During testing, the films were exposed to an H(2)O(2)/CoCl(2) solution, which simulated the oxidative component of the in vivo environment. Films treated for up to 24 days were evaluated by IR spectroscopy and by optical and scanning electron microscopy. Biostability of a poly(ether urethane) (PEU), which is known to undergo oxidative degradation, was compared with biostability of a poly(carbonate urethane) (PCU), which is thought to be more resistant to oxidation than PEU. Materials similar to PEU and PCU, in which the polyether or polycarbonate soft segment was partially replaced with poly(dimethylsiloxane) (PDMS), were also tested with the expectation that PDMS would improve soft-segment biostability. Oxidative degradation of the polyether soft segment of PEU was manifest chemically as chain scission and cross-linking and physically as surface pitting. Biaxial fatigue accelerated chemical degradation of PEU and eventually caused brittle stress cracking. In comparison, the polycarbonate soft segment was more stable to oxidation; there was minimal chemical or physical degradation of PCU, even in biaxial fatigue. Partial substitution of the polyether soft segment with PDMS enhanced oxidative stability of PEU. Although both strategies for modifying soft-segment chemistry improved the resistance to oxidative degradation, the outstanding mechanical properties of PEU were compromised to some extent.

Biocompatible Materials↗