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At least 109 records · Page 6Linked to original sources
PubMed2003

Turkish Tombul hazelnut (Corylus avellana L.). 2. Lipid characteristics and oxidative stability.

The quality of crude hazelnut oil extracted from Tombul (Round) hazelnut, grown in the Giresun province of Turkey, was determined by measuring lipid classes, fatty acids, and fat soluble bioactives (tocopherols and phytosterols). Oxygen uptake, peroxide value, thiobarbituric acid reactive substances, and alpha-tocopherol levels of stripped and crude hazelnut oils in bulk and oil-in-water (o/w) emulsion systems were also evaluated as indices of lipid oxidation over a 21 day storage period at 60 degrees C in the dark. The total lipid content of Tombul hazelnut was 61.2%, of which 98.8% were nonpolar and 1.2% polar constituents. Triacylglycerols were the major nonpolar lipid class and contributed nearly 100% to the total amount. Phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol were the most abundant polar lipids, respectively. Sixteen fatty acids were identified, among which oleic acid contributed 82.7% to the total, followed by linoleic, palmitic, and stearic acids. Unsaturated fatty acids accounted for 92.2% of the total fatty acids present. Among oil soluble bioactives, alpha-tocopherol (38.2 mg/100 g) and beta-sitosterol (105.5 mg/100 g) were predominant in hazelnut oil and comprised 88 and 93% of the total tocopherols and phytosterols present, respectively. The results also showed that both stripped and crude hazelnut oils were more stable in terms of lipid oxidation in the bulk oil as compared to those in an o/w emulsion.

Corylus↗
PubMed1999

Comparison of three methods based on electron spin resonance spectrometry for evaluation of oxidative stability of processed cheese.

Electron spin resonance (ESR) spectrometry has been adapted to accelerated (light and temperature) storage experiments with processed cheese comparing the spin trapping technique with 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) as spin trap added to the cheese and the spin labeling technique with 2,2,6, 6-tetramethylpiperidine-1-oxyl radical (TEMPO) as spin label added to the cheese. Both methods showed that light was the more important factor compared to temperature for early stages (up to 11 days) in the formation of radicals in processed cheese. For the spin labeling technique other, unidentified reactions interfered during the early stages of the accelerated storage, indicating that longer reaction times are required for the evaluation, and the spin trapping technique is recommended. As a third method, direct measurement of free radicals formed in processed cheese stored for 15 months and subsequently freeze-dried showed that for longer storage, temperature is more important for the steady-state concentration of radicals than light exposure. In agreement with this result, formation of secondary lipid oxidation products determined as thiobarbituric acid reactive substances was found to correlate with the direct ESR measurement.

Cheese↗
PubMed2001

Oxidative stability of dark chicken meat through frozen storage: influence of dietary fat and alpha-tocopherol and ascorbic acid supplementation.

We used factorial design to ascertain the influence of dietary fat source (linseed, sunflower and oxidized sunflower oils, and beef tallow) and the dietary supplementation with alpha-tocopheryl acetate (alpha-TA) (225 mg/kg of feed) and ascorbic acid (AA) (110 mg/kg) on dark chicken meat oxidation (lipid hydroperoxide and TBA values and cholesterol oxidation product content). alpha-TA greatly protected ground and vacuum-packaged raw or cooked meat from fatty acid and cholesterol oxidation after 0, 3.5, or 7 mo of storage at -20 C. In contrast, AA provided no protection, and no synergism between alpha-TA and AA was observed. Polyunsaturated fatty acid-enriched diets (those containing linseed, sunflower, or oxidized sunflower oils) increased meat susceptibility to oxidation. Cooking always involved more oxidation, especially in samples from linseed oil diets. The values of all the oxidative parameters showed a highly significant negative correlation with the alpha-tocopherol content of meat.

Animal Feed↗
PubMed2004

Oxidative stability of buttermilk as influenced by the fatty acid composition of cows' milk manipulated by diet.

Milk from cows fed a low-fat diet high in cereals designed to stimulate fat synthesis de novo was lower in unsaturated fatty acids (21.3%) than milk from cows fed a diet high in fat, mainly from roasted soy beans (41.3% unsaturated fatty acids). Buttermilk from the more unsaturated milk was less oxidatively stable during storage (at 4 degrees C, followed for 11 d) than buttermilk from the more saturated milk, as monitored both by primary lipid oxidation products (lipid hydroperoxides) and by the secondary lipid oxidation product, hexanal. Fat-soluble antioxidants, beta-carotene and alpha-tocopherol, analysed by HPLC, were not consumed during storage for either of the two types of buttermilk. In contrast, the antioxidative capacity of the serum phase decreased during storage as evaluated in a radical scavenging assay based on the semi-stable water-soluble radical nitrosodisulphonate (Fremy's salt). The time course for the decrease in water-soluble antioxidants was very similar for the two types of buttermilk suggesting that oxidation is initiated in the serum phase independently of fatty acid composition.

Animals↗
PubMed2000

Effect of dietary iron and copper on performance and oxidative stability in broiler leg meat.

1. An experiment was carried out to determine the effect of removal of supplemental iron and copper from broiler diets during the last 3 weeks before slaughter on broiler performance, tissue vitamin E concentrations and oxidation values in raw; cooked and stored broiler leg meat. 2. Removal of supplemental iron and copper from the diet slightly decreased food efficiency; the differences were significant only when both minerals were removed simultaneously 3. Effect of iron withdrawal on iron concentration in tissue was low. However, total copper concentration in tissue was reduced in animals deprived of iron or both minerals simultaneously. 4. Removal of dietary iron and copper did not affect vitamin E concentration in raw and cooked meat, while stored meat showed lower concentrations in animals deprived of iron and copper simultaneously. 5. The removal of iron and copper from the diet reduced oxidation values in cooked broiler leg meat as measured by the thiobarbituric acid-reacting substances method (TBARS).

Animals↗
PubMed2006

Oxidative stabilization of iso-1-cytochrome c by redox-inspired protein engineering.

Iso-1-cytochrome c, as any other hemeprotein, is able to react with hydrogen peroxide and to engage in the peroxidase cycle. However, peroxidases are irreversibly inactivated by their substrate, hydrogen peroxide. The oxidative inactivation of hemeproteins is mechanism based and arises as the consequence of unproductive electron abstraction reactions. Protein elements, such as the porphyrin ring or the protein backbone, act as simultaneous and competing electron sources even in the presence of exogenous reducing substrates, leading to a decline in activity. It is hypothetically possible to alter the intramolecular electron transfer pathways by direct replacement of low redox potential residues around the active site; as a consequence, the inactivation process would be delayed or even suppressed. To demonstrate this hypothesis, a redox-inspired strategy was implemented until an iso-1-cytochrome c variant fully stable at catalytic concentrations of hydrogen peroxide was obtained. This variant, harboring the N52I,W59F,Y67F,K79A,F82G substitutions, preserved the catalytic performance of the parental protein but achieved a 15-fold higher total-turnover number. The phenotype of this variant was reflected in the stability of its electronic components, allowing identification of a protein-based radical intermediate mechanistically similar to Compound I of classical peroxidases. The results presented here clearly demonstrate that redox-inspired protein engineering is a useful tool for the rational modulation of intramolecular electron transfer networks.

Amino Acid Sequence↗
PubMed2004

Performance of rabbits and oxidative stability of muscle tissues as affected by dietary supplementation with oregano essential oil.

The effect of dietary supplementation with oregano essential oil on the performance of rabbits, and the susceptibility of the produced raw and thermally treated muscle tissue to lipid oxidation during refrigerated storage, were investigated. A total of 96 weaned rabbits were separated into four equal groups with three subgroups each. One group was given the basal diet and served as control, two groups were administered diets supplemented with oregano essential oil at levels of 100 and 200 mg/kg diet, whereas the remaining group was given a diet supplemented with alpha-tocopheryl acetate at 200 mg/kg. During the 42-day experimental period, body weight and feed intake were recorded weekly and the feed conversion ratio was calculated. Feeding the experimental diets to rabbits, performance parameters were not affected. Therefore, dietary oregano essential oil exerted no growth-promoting effect on rabbits. With increased supplementation of oregano essential oil, malondialdehyde values decreased in both raw and thermally treated muscles during refrigerated storage. This finding suggests that dietary oregano essential oil exerted a significant antioxidant effect. Dietary supplementation of oregano essential oil at the level of 200 mg/kg was more effective in delaying lipid oxidation compared with the level of 100 mg/kg, but inferior to dietary supplementation of 200 mg alpha-tocopheryl acetate per kg. This study indirectly provides evidence that antioxidant compounds occurring in oregano essential oil were absorbed by the rabbit and increased the antioxidative capacity of tissues.

Animals↗
PubMed1990

Liposomes composed of partially hydrogenated egg phosphatidylcholines: fatty acid composition, thermal phase behavior and oxidative stability.

Partially hydrogenated egg phosphatidylcholines (PHEPC) represent a new class of raw materials for liposome-based drug products. PHEPC were manufactured from native egg phosphatidylcholine (EPC) to iodine values (IV) 40, 30, 20, 10, and 1. Hydrogenation resulted in a complete loss of arachidonic acid (20:4) and docosahexaenoic acid (22:6) in IV 40 EPC and a progressive conversion of linoleic (18:2) and oleic acid (18:1) to stearic acid (18:0) at higher degrees of hydrogenation (IV 30, 20, 10, 1). Hydrogenation lead to formation of trans-fatty acid isomers maximally 18.5 mol% in IV 20 EPC. Liposomes made from IV 20, IV 10 and IV 1 EPC had marked phase transitions between 20 and 60 degrees C. PHEPC showed increased resistance to oxidation as measured by oxygen uptake during 2,2'-azobis-(2-amidinopropane) hydrochloride (AAPH) initiated accelerated oxidation. Various applications of these new materials in the manufacture of liposomes and liposome based drug products are discussed.

Chemical Phenomena↗
PubMed2005

Effects of dietary supplementation with copper sulfate or tribasic copper chloride on broiler performance, relative copper bioavailability, and oxidation stability of vitamin E in feed.

An experiment was conducted using a total of 420, 1-d-old, Arbor Acres commercial male chicks to compare copper sulfate and tribasic copper chloride (TBCC) as sources of supplemental copper for broilers. Chicks were randomly allotted to 1 of 7 treatments for 6 replicates of 10 birds each and were fed a basal corn-soybean meal diet (11.45 mg/kg copper) supplemented with 0, 150, 300, or 450 mg/kg copper from copper sulfate or TBCC for 21 d. Chicks fed 450 mg/kg copper as copper sulfate had lower (P < 0.01) average daily feed intake and average daily gain than those consuming other diets. Feeding supplemental copper increased linearly (P < 0.0001) liver copper concentrations regardless of copper source. The slopes of regressions of log10 liver copper on different independent variables used in regressions differ (P < 0.05) between the 2 copper sources. Linear regression over nonzero dietary levels of log10 transformed liver copper concentration on added copper intake resulted in a slope ratio estimate of 109.0 +/- 3.4% (with a 95% confidence interval from 102.2 to 115.8) for bioavailability of copper from TBCC compared with 100 for that in copper sulfate. When the feeds were stored at room temperature for 10 or 21 d, the vitamin E content in the feed fortified with 300 mg/kg copper as TBCC was higher (P < 0.01) than that in the feed added with 300 mg/kg copper as CuSO4. The vitamin E contents in liver and plasma of broilers given TBCC were also higher (P < 0.01) than those of birds fed copper sulfate. The results from this study indicate that TBCC is a safer product and more available to broilers than copper sulfate, and it is chemically less active than copper sulfate in promoting the oxidation of vitamin E in feed.

Animal Feed↗
PubMed2000

Impact of dietary conjugated linoleic acid on the oxidative stability of rat liver microsomes and skeletal muscle homogenates.

Dietary conjugated linoleic acid (CLA; 0-2.0%) increased CLA concentrations in liver microsomes and skeletal muscle homogenates from rats. Dietary CLA decreased oleic and arachadonic acid concentrations in both liver microsomes and skeletal muscle. The presence of CLA in liver microsomes had no impact on linoleic acid, arachadonic acid, and alpha-tocopherol oxidation rates. Dietary CLA (2.0%) also did not alter alpha-tocopherol oxidation rates in liver microsomes or muscle homogenates. Formation of malonaldehyde (MDA) in oxidizing liver microsomes decreased with increasing CLA concentration as determined by measurement of thiobarbituric acid-MDA complexes by HPLC. The ability of CLA to decrease MDA formation without impacting other lipid oxidation markers such as the disappearance of fatty acid and alpha-tocopherol suggests that decreased MDA concentration was the result of CLA's ability to lower polyenoic fatty acids such as arachadonic acid. While CLA does not appear to act as an antioxidant, its ability to decrease polyenoic fatty acid concentrations could decrease the formation of highly cytotoxic lipid oxidation products such as MDA.

Animals↗