PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Oxidative stability”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources
PubMed2002

The effect of virtual cross linking on the oxidative stability and lipid uptake of aliphatic poly(urethane urea).

In vitro oxidative degradation and lipid sorption of aliphatic, low elastic modulus and virtually cross-linked poly(urethane urea)s based on 4,4' methylene bis(cyclohexyl isocyanate), hydroxy terminated poly butadiene and hexamethylene diamine were evaluated. The aged samples revealed no weight loss in the oxidation medium. The IR spectral analyses revealed the stability of unsaturated double bonds at 964 cm(-1) (characteristic for polybutadiene soft segment) with no change in peak intensity. The poly(tetramethylene glycol) (PTMG)-added poly(ether urethane urea) polymer also revealed no disappearance of IR peaks for ether and unsaturated double bonds in samples aged in vitro oxidation medium. All the polymers have shown increase in weight due to lipid up take in lipid-rich medium (palm oil) but it was rather low in Dulbecco's modified eagle medium (DMEM) cholesterol. The slight change in mechanical properties of the present polymers in oxidation and DMEM is due to the rearrangement of molecular structure with virtual cross links of hydrogen bonding (physical cross linking) without degradation and plasticization effect of lipid. The influence of these media on the rearrangement of virtual cross links has been observed. Higher the virtual cross-link density, lesser is the loss of tensile properties of poly(urethane urea)s in the oxidation medium and vice versa. On the other hand, higher the virtual cross-link density of poly(urethane urea), higher is the loss of ultimate tensile strength and stress at 100% strain and vice versa in DMEM medium.

Evaluation Studies as Topic↗
PubMed1995

Proteins lose their nitric oxide stabilizing function after advanced glycosylation.

In vivo generated nitric oxide, NO, circulates in plasma mainly as an S-nitroso adduct of serum albumin. Compared to free NO, this NO-adduct is relatively long-lived. It exerts EDRF-like effects of vasodilation and platelet inhibition. Free NO is directly inactivated ('quenched') by advanced glycosylation end products (AGEs), glucose-derived protein moieties that form nonenzymatically and accumulate primarily on long-lived tissue proteins. They have been implicated in many of the long-term complications of diabetes mellitus. We found that the antiproliferative effects of thiol-stabilized NO (SNO-BSA) on Con A-stimulated lymphocytes from peripheral blood were even stronger than those of the NO-generating drug SNAP. The antimitogenic activity of SNO-BSA, however, was not significantly enhanced by the low molecular weight NO-carrier glutathione. NO liberated from SNO-BSA in molar excess was almost completely quenched by AGE-BSA. NO-dependent activating effects such as enhanced rate of glucose uptake or generation of cGMP in resting peripheral mononuclear cells (PBMC) and the antiproliferative activity of the NO-carrier BSA on Con A-stimulated cells were thereby abolished. In contrast, advanced glycosylation impaired the ability of BSA to function as NO-carrier, as evidenced by the lack of antiproliferative activity of NO-AGE-BSA and its inability to activate glucose transport or cGMP generation.

Blood Proteins↗
PubMed2006

Influence of crystallization on the oxidative stability of extra virgin olive oil.

The aim of this study was to evaluate the influence of the extra virgin olive oil (EVOO) physical state on the kinetics of oxidative reactions. To this purpose, EVOO was stored at increasing temperatures from 3 to 60 degrees C and the oxidation was followed by measuring both primary and secondary oxidation products. Results highlighted that crystallization plays an important role in determining EVOO stability. Below the melting point, the oxidation rate was found to be higher than that expected on the basis of the Arrhenius equation. The observed deviation from the Arrhenius equation was attributed to the physicochemical changes occurring as a consequence of phase transitions. In particular, the increase in unsaturated triacylglycerol concentration and the decrease of polyphenol content in the liquid phase surrounding fat crystals were indicated as the main factors causing the deviation. By taking into account these changes it was possible to describe the temperature dependence of the oxidation rate in the entire range of temperatures considered. This model appears to be promising in the challenge to find mathematical models able to predict the stability and, hence, the shelf life of lipid-containing foods.

Chemical Phenomena↗
PubMed2003

Trimethylamine N-oxide stabilizes RNA tertiary structure and attenuates the denaturating effects of urea.

Trimethylamine N-oxide (TMAO) and urea are osmolytes. Osmolytes allow cells to remain viable in harsh or extreme environments. Both TMAO and urea are found in shark and rays at approximate molar ratios of 1:2, respectively. At this ratio TMAO nearly completely counteracts the destabilizing effects that urea has on proteins. We ask whether RNA, which is denatured by urea, is stabilized by TMAO in a manner similar to that seen for proteins. We found that TMAO stabilizes Escherichia coli tRNAfmet tertiary structure and counteracts the denaturing effects of urea at the same ratios found for proteins. Cation binding usually drives RNA tertiary structure formation. These results suggest that tertiary structure stability is not only sensitive to cations but also to the aqueous composition and properties of the solvent. We propose that tertiary structure folding is driven by unfavorable interactions between TMAO and the phosphodiester backbone.

Escherichia coli↗
PubMed2003

Effect of sumach (Rhus coriaria L.) extracts on the oxidative stability of peanut oil.

The antioxidant activities of sumach (Rhus coriaria L.) extracts and butylated hydroxyanisole (BHA) at various concentrations were tested in natural peanut oil stored at 65 degrees C for 35 days. The concentrations (weight/volume) of extracts added into oil were 1.0%, 3.0%, and 5.0%, and those of BHA were 0.1%, 0.3%, and 0.5%. Antioxidant effect was determined by the measurement of peroxide value. After 7 days of storage, BHA and extracts of sumach were active in varying degrees against autoxidation of peanut oil, compared with the control test (P <.01). The sumach extracts generally inhibited the formation of hydroperoxide, as did BHA. After 28 days of storage, antioxidant effects of extracts were significantly decreased when compared with BHA. The decrease in the antioxidant activity of extracts might have resulted from the decrease of polyphenolic constituents. The results showed that high concentrations can enhance the potency of the antioxidant effect of sumach extract.

Antioxidants↗
PubMed1999

Trimethylamine oxide stabilizes teleost and mammalian lactate dehydrogenases against inactivation by hydrostatic pressure and trypsinolysis.

Trimethylamine N-oxide (TMAO) is an organic osmolyte present at high levels in elasmobranchs, in which it counteracts the deleterious effects of urea on proteins, and is also accumulated by deep-living invertebrates and teleost fishes. To test the hypothesis that TMAO may compensate for the adverse effects of elevated pressure on protein structure in deep-sea species, we studied the efficacy of TMAO in preventing denaturation and enhanced proteolysis by hydrostatic pressure. TMAO was compared to a common 'compatible' osmolyte, glycine, using muscle-type lactate dehydrogenase (A(4)-LDH) homologs from three scorpaenid teleost fish species and from a mammal, the cow. Test conditions lasted 1 h and were: (1) no addition, (2) 250 mmol l(-)(1) TMAO and (3) 250 mmol l(-)(1) glycine, in the absence and presence of trypsin. Comparisons were made at 0. 1 and 101.3 MPa for the deeper occurring Sebastolobus altivelis, 0.1, 50.7 and 101.3 MPa for the moderate-depth congener S. alascanus, 0. 1 and 25.3 MPa for shallow-living Sebastes melanops and 0.1 and 50.7 MPa for Bos taurus. Susceptibility to denaturation was determined by the residual LDH activity. For all the species and pressures tested, 250 mmol l(-)(1) TMAO reduced trypsinolysis significantly. For all except S. altivelis, which was minimally affected by 101.3 MPa pressure, TMAO stabilized the LDH homologs and reduced pressure denaturation significantly. Glycine, in contrast, showed no ability to reduce pressure denaturation alone, and little or no ability to reduce the rate of proteolysis.

Analysis of Variance↗
PubMed2005

Oxidative stability and phenolic content of virgin olive oil: an analytical approach by traditional and high resolution techniques.

The characteristic resistance to oxidation of virgin olive oil is related to its unique fatty acid composition in addition to several minor components that have antioxidant properties. Among the latter, phenols are the most important. Several factors can influence the chemical or enzymatic oxidative processes that extend or shorten the shelf-life of olive oil. Furthermore, the amount of phenolic compounds extracted during production is fundamental for the oxidative and nutritional quality of the oil. In fact, it is well known that different steps used for preparation of virgin olive oil may determine differences in the quantities of phenol. At present, various analytical methods are available to analyze the hydrophilic components, including spectrophotometric assays (traditional) and high resolution chromatographic techniques (HRGC, HPLC, HPCE). In this review we summarize these different methodologies and demonstrate that the amount of phenolic compounds in virgin olive oil as determined by both traditional and high resolution techniques can be influenced by different factors including the olive cultivar and degree of ripeness, as well as by production and extraction technologies.

Chromatography, High Pressure Liquid↗
PubMed2005

Evaluation of oxidation stability of lignite humic substances by DSC induction period measurement.

The stability of lignite humic acids and four regenerated humic acids was estimated by employing differential scanning calorimetry. Induction period for the oxidative decomposition of humic matter was calculated from non-isothermal measurements at six different rates of heating. To simulate the gradual evolution history of humic acids, different intensities of oxidation attack by nitric acid on the original lignite was used. Experimental data showed higher stability of natural humic acids in the temperature range where the decomposition step occurred. On the other hand, extrapolation to lower temperatures and calculated kinetic parameters did not correspond to the order observed at higher temperatures. An oscillating trend of calculated parameters of the two proposed parts of stability was observed, which agreed with data concerning regenerated humic acids production. The approach applied in this work represents a rapid and useful method for evaluation of organic matter stability.

Calorimetry, Differential Scanning↗
PubMed2001

Deduced amino-acid sequence of a calcium-free alpha-amylase from a strain of Bacillus: implications from molecular modeling of high oxidation stability and chelator resistance of the enzyme.

Alkaline alpha-amylase (AmyK38) from the alkaliphilic Bacillus sp. strain KSM-K38 is a unique enzyme in that it is highly chelator-resistant and oxidatively stable [Hagihara, H., Igarashi, K., Hayashi, Y., Endo, K., Ikawa-Kitayama, K., Ozaki, K., Kawai, S. & Ito, S. (2001) Appl. Environ. Microbiol. 67, 1744-1750]. This enzyme was found to contain no Ca and require Na (or monovalent cations) for manifestation of activity. The nucleotide sequence of the gene for the novel enzyme was determined, and it harbored an ORF of 1503 bp encoding the enzyme of 501 amino acids, including a 21-amino-acid signal peptide. The deduced amino-acid sequence of the mature enzyme (55 097 Da) showed moderate homology to those of alpha-amylases from Bacillus licheniformis, Bacillus stearothermophilus and Bacillus amyloliquefaciens, with approximately 63% identity. A methionine residue, which is conserved and susceptible to chemical oxidation, was replaced with leucine in AmyK38. Moreover, many conserved residues that are crucial ligands for Ca were replaced with other amino acids, thereby leading to loss of the Ca coordination geometries. By building a molecular model, we showed the calcium-independent, oxidatively stable active-site topology and structural integrity of AmyK38.

Alkalies↗
PubMed2006

Protective effects of extra virgin olive oil phenolics on oxidative stability in the presence or absence of copper ions.

The antioxidant activity of the phenolic fraction of extra virgin olive oil was assessed in samples that had a decreasing content of antioxidants in the presence and absence of copper ions as a catalyst of autoxidation. The oxidation process was evaluated by measuring primary and secondary oxidation products. Changes in phenols and tocopherols were investigated by high-performance liquid chromatography. Both the total phenol content and their antioxidant activity were monitored by spectrophotometric assays (with Folin-Ciocalteu and ABTS*+ reagents). The important role of phenolic compounds (particularly the o-diphenols) in protection from autoxidation was confirmed. However, the tocopherols were more quickly consumed in oils that had the lowest content of o-diphenols, which also showed evidence of an ability to chelate copper. In particular, a dramatic decrease was observed in the isomeric form of decarboxymethyl-oleuropein aglycone after addition of the metal, despite its significant increase in samples stored in the absence of copper.

Antioxidants↗
PubMed2002

Novel approach to study oxidative stability of extra virgin olive oils: importance of alpha-tocopherol concentration.

The stability of extra virgin olive oils is mainly due to their relatively low fatty acids unsaturation and to the antioxidant activity of some of the unsaponifiable components. We studied the activity of alpha-tocopherol in extra virgin olive oil in its natural state, using new and simple oxidizing conditions in "thin layer" and "bulk phase". Oxidation time course was monitored at 37 degrees C or 75 degrees C. A storage test was also performed. Two parameters were evaluated: depletion of alpha-tocopherol and formation of PUFA hydroperoxides, measured as conjugated dienes (CD) and peroxide value. The value of complex polyphenols was also measured. alpha-Tocopherol concentration decreased in function of time and temperature and showed a strong inverse correlation with the increase of CD. When alpha-tocopherol reached a "threshold value" of 60-70 mg/kg, a significant increase of CD formation was observed, together with a good correlation between CD and peroxide value. The initial amount of alpha-tocopherol is one of the components that influences oil oxidative susceptibility.

Antioxidants↗
PubMed2006

Acidolysis reactions lead to esterification of endogenous tocopherols and compromised oxidative stability of modified oils.

For the first time, a possible mechanism responsible, in part, for the removal of endogenous antioxidants through the formation of tocopheryl esters during acidolysis reactions is proposed and confirmed. Tocopherols in the oils were found to react with carboxylic acids present in the medium, thus leading to the formation of tocopheryl esters that do not render any stability to the resultant modified oils as they lack any free hydroxyl groups on the phenolic ring of the molecule. Tocopheryl oleate, used as a standard, was synthesized through the reaction of acyl chloride of oleic acid with alpha-tocopherol (m/z 695.5 as evidenced by mass spectrometry). Subsequently, lipase-assisted esterification of alpha-, gamma-, and delta-tocopherols with oleic acid was carried out, and corresponding tocopheryl esters were isolated. In a real acidolysis reaction system involving docosahexaenoic acid single-cell oil and capric acid, high-performance liquid chromatography-mass spectrometry analysis demonstrated the presence of several tocopheryl esters. These included tocopheryl esters of myristic acid, namely, alpha-tocopheryl myristate, m/z 641.1, gamma-tocopheryl myristate, m/z 627.1, and delta-tocopheryl myristate, m/z 613.1, as well as those of palmitic acid, namely, alpha-tocopheryl palmitate, m/z 669.1, gamma-tocopheryl palmitate, m/z 655.1, and delta-tocopheryl palmitate, m/z 641.1. The mixture also contained different species of tocopheryl oleates, namely, alpha-tocopheryl oleate, m/z 695.5, gamma-tocopheryl oleate, m/z 681.1, and delta-tocopheryl oleate, m/z 667.2. Esters produced from reactions of docosahexaenoic acid and tocopherols were also detected, namely, alpha-tocopheryl docosahexaenoate, m/z 738.7, and delta-tocopheryl docosahexaenoate, m/z 710.7.

Acids↗
PubMed1999

Effect of lactoferrin on oxidative stability of corn oil emulsions and liposomes.

Interest in using lactoferrin in foods for its antimicrobial activity inspired the present study of its antioxidant activity. Natural bovine lactoferrin inhibited oxidation in buffered corn oil emulsions and lecithin liposome systems at pH 6.6 and 50 degrees C. The antioxidant activity increased with lactoferrin concentration in both phosphate- and Tris-buffered emulsions, but not in both buffered liposome systems. A mixture of 1 microM lactoferrin and 0.5 microM ferrous ions was a significantly better antioxidant than 1 microM lactoferrin alone in Tris-buffered emulsions and in phosphate-buffered liposomes. Lactoferrin was a prooxidant at 1 microM in phosphate-buffered liposomes and at 15 and 20 microM in Tris-buffered liposomes. Copper was a stronger prooxidant than iron in both buffered emulsions. Lactoferrin decreased the prooxidant effect of iron, but not of copper, in emulsions. The antioxidant or prooxidant activities of lactoferrin depended on the lipid system, buffer, its concentration, the presence of metal ions, and oxidation time.

Animals↗
PubMed1975

Insulin-sensitive phosphodiesterase. Its localization, hormonal stimulation, and oxidative stabilization.

As it was shown previoulsy by others, the membrane-bound phosphodiesterase (cyclic adenosine 3':5'-monophosphate phosphodiesterase) of rat epididymal fat cells was stimulated when intact cells were exposed to insulin. The levels of stimulation observed in the present study in the cell homogenate and microsomal fraction were approximately 2.0- to 2.5-fold and 2.5- to 3.0-fold, respectively, when the initial substrate level was 100 nM and insulin concentration was 1 to 3 nM. When the microsomal fraction was subjected to a sucrose density gradient centrifugation, most of the insulin-sensitive phosphodiesterase activity was fractionated into the "light" microsomal fraction which was rich in NADH2:potassium ferricyanide:oxidoreductase) and low in 5'-AMPase, adenylate cyclase, and insulin-binding activities. The latter three activities were mostly fractionated into the "heavy" microsomal fraction. Both basal and insulin-stimulated phosphodiesterase activities were low when cells were homogenized in the presence of N-ethylmaleimide or p-chloromercuribenzoate. The insulin-stimulated enzyme activity was also low when cells were homogenized in the presence of --SH compounds (e.g. dithiothreitol) or certain metal-chelating agents (e.g. ethylene glycol bis(beta-aminoethyl ehter)-N,N'-tetraacetate (EGTA)), or in a nitrogen atmosphere. The effect of EGTA was prevented by the addition of certain heavy metal ions but not by the addition of Ca2+ or Ca2+ plus Mg2+ ions. When cells were homogenized in the presence of certain oxidants (e.g. diamide, sodium tetrathionate, or air), a high plus-insulin activity was observed; this activity was not lowered by subsequent treatment of the enzyme with N-ethylmaleimede, EGTA, or fresh cell homogenate that was prepared in the presence of EGTA. However, the activity of an apparently oxidized enzyme could still be lowered by treatment woth dithiothreitol. A partially purified enzyme in the enzyme in the microsomal fraction was fairly stable both in basal and insulin-stimulated states (fully active after 35 days when kept at -20degrees). EGTA added to the homogenization buffer lowered the basal phosphodiesterase activity, but this effect was reversed by the addition of Ca2+ ions. EGTA also decreased the enzyme activity that was stimulated by norepinephrine. However, neither EGTA nor dithiothreitol had any effect on the activities of 5'-AMPase, NADH-dehydrogenase, and malate dehydrogenase of fat cells. The above data indicate that most of the insulin-sensitive phosphodiesterase and the so-called "cell membrane markers" are associated with different subcellular particles in the cell homogenate. In addition, the data seem to indicate that the insulin-stimulated phosphodiesterase has certain --SH groups and that the activity of the enzyme is stabilized when the --SH groups are oxidized by certain oxidants including molecular oxygen. It is suggested that the air oxidation of the enzyme is catalyzed by a trace of certain heavy metal ions and, therefore, can be blocked by a metal-chelating agent.

3',5'-Cyclic-AMP Phosphodiesterases↗