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排序方式: 共有64条查询结果,搜索用时 15 毫秒
1.
Analysis of lipid classes by solid-phase extraction and high-performance size-exclusion chromatography 总被引:1,自引:0,他引:1
Anu I. Hopia Vieno I. Piironen Pekka E. Koivistoinen Lea E. T. Hyvönen 《Journal of the American Oil Chemists' Society》1992,69(8):772-776
An improved method to analyze lipid classes of edible oils and fats by solid-phase extraction (SPE) and high-performance size-exclusion chromatography (HPSEC) is presented. A mixture of lipid standards was fractionated by the solid-phase extraction procedure (NH2 phase) into polar and nonpolar fractions; these were then submitted to analysis by HPSEC. The size-exclusion chromatographic columns were three styrene/divinylbenzene columns with pore sizes of 100 Å and 50 Å. Light-scattering was used for the detection system, and the parameters of the detector were optimized to minimize the difference between the responses of the compounds studied. With this procedure it was possible to separate the following lipid classes: triacylglycerols, diacylglycerols, monoacylglycerols and free fatty acids, sterols, sterol esters, tocopherols and carotenoids. Quantitative analysis was studied for a light-scattering detector with several lipid standards of different molecular weights and unsaturation levels. 相似文献
2.
Marina Heinonen Katri Haila Anna-Maija Lampi Vieno Piironen 《Journal of the American Oil Chemists' Society》1997,74(9):1047-1052
The effects of low concentrations of β-carotene, α-, and γ-tocopherol were evaluated on autoxidation of 10% oil-in-water emulsions
of rapeseed oil triacylglycerols. At concentrations of 0.45, 2, and 20 μg/g, β-carotene was a prooxidant, based on the formation
of lipid hydroperoxides, hexanal, or 2-heptenal. In this emulsion, 1.5, 3, and 30 μg/g of γ-tocopherol, as well as 1.5 μg/g
of α-tocopherol, acted as antioxidants and inhibited both the formation and decomposition of lipid hydroperoxides. Moreover,
at a level of 1.5 μg/g, γ-tocopherol was more effective as an antioxidant than α-tocopherol. At levels of 0.5 μg/g, both α-
and γ-tocopherol significantly inhibited the formation of hexanal but not the formation of lipid hydroperoxides. Oxidation
was effectively retarded by combinations of 2 μg/g β-carotene and 1.5 μg/g γ- or α-tocopherol. The combination of β-carotene
and α-tocopherol was significantly better in retarding oxidation than α-tocopherol alone. While γ-tocopherol was an effective
antioxidant, a synergistic effect between β-carotene and γ-tocopherol could not be shown. The results indicate that there
is a need to protect β-carotene from oxidative destruction by employing antioxidants, such as α- and γ-tocopherol, should
β-carotene be used in fat emulsions. 相似文献
3.
T Piironen BO Villoutreix C Becker K Hollingsworth M Vihinen D Bridon X Qiu J Rapp B Dowell T L?vgren K Pettersson H Lilja 《Canadian Metallurgical Quarterly》1998,7(2):259-269
In comparison with pyeloplasty, endourologic procedures for the treatment of ureteropelvic junction obstruction offer good success rates with less morbidity and a shorter hospitalization; however, studies have found lower success rates and increased complications in patients with crossing vessels. Conventional diagnostic angiography and intravenous urography have both been used to identify crossing vessels at the UPJ; but, a reliable, less invasive, less costly, and simpler preoperative procedure to identify crossing vessels is needed. Helical CT with CT angiography is a promising noninvasive technique for the identification of crossing vessels at the ureteropelvic junction, which can be used for surgical planning of endourologic treatment of UPJ obstruction. 相似文献
4.
Dimer formation during the thermo-oxidation of stigmasterol 总被引:1,自引:1,他引:0
Karin Struijs Anna-Maija Lampi Velimatti Ollilainen Vieno Piironen 《European Food Research and Technology》2010,231(6):853-863
The monomeric oxidation products formed during the thermo-oxidation of phytosterols do not explain the loss of unoxidized
phytosterols, leaving a gap in the knowledge on the products that are being formed during thermo-oxidation. Previous research
showed that the gap can be explained by the formation of dimers and polymers. The aim of this research was to investigate
the dimers that are formed during the thermo-oxidation of phytosterols, using stigmasterol as a model compound. Following
the oxidation of stigmasterol at 180 °C, several dimeric fractions were obtained by solid phase extraction and high-performance
size-exclusion chromatography. Individual dimers were separated by reversed-phase high-performance liquid chromatography,
and their molecular masses were determined by combining atmospheric pressure chemical ionization-mass spectrometry and coordination-ion
spray-mass spectrometry. This study resulted, for the first time, in the assignment of several individual stigmasterol dimers.
The most dominant dimer was found to have a molecular mass of 822.7 Da and is suggested to represent a C–C linked dimer of
stigmasterol, in accordance with literature. Several other stigmasterol dimers were found to be formed during thermo-oxidation,
which are suggested to differ in monomeric subunit composition, linkage type, and stereochemistry. 相似文献
5.
Laura Soupas Laura Juntunen Suvi Säynäjoki Anna-Maija Lampi Vieno Piironen 《Journal of the American Oil Chemists' Society》2004,81(2):135-141
A new GC-MS method for characterization and quantification of phytosterol oxidation products was developed. Applicability
of this method was tested by characterizing sitostanol oxides formed in bulk and then quantifying selected oxides in purified
rapeseed oil and tripalmitin matrices in which the complex matrix made oxide analysis difficult. In bulk, nine different sitostanol
oxides were characterized, including epimers of 7- and 15-hydroxysitostanol and 6- and 7-ketositostanol. In both lipid matrices,
the amounts of sitostanol oxides generated in thermo-oxidation were very low. According to statistical analyses, depending
on the oxide, the GC-MS results were the same or slightly higher than those quantified by the more common GC-FID method. Thus,
GC-MS provides a powerful alternative for characterization and quantification of phytostanol oxides found in low amounts in
complex matrices and is a promising method for future phytosterol oxide studies. 相似文献
6.
Gintaras Baltrūnas Aušra Valiūnienė Justas Vienožinskis Ernestas Gaidamauskas Teofilis Jankauskas Žana Margarian 《Journal of Applied Electrochemistry》2008,38(11):1519-1526
Electrochemical gold deposition from sulfite solutions was studied by means of voltammetry, EIS and EQCM. A gold film electrode
was used for polyaniline layer formation by electrochemical oxidation of aniline. The standard electrochemical reduction potential
of the reaction [Au(SO3)2]3− + e− = Au + 2 SO32− was determined, and is equal to 0.116 V (vs. NHE). Both solution stirring and temperature increase accelerate the electrochemical
reduction of gold, when the electrode potential is below −0.55 V. When the potential is above −0.55 V the electrochemical
reduction proceeds via passive layer formation. Our study suggests that the passive layer consists of chemically adsorbed
sulfite ions and sulfur. The gold film deposited from sulfite solution is a high quality substrate suitable for conducting
polymer layer formation. This technique, where a polymer layer electrode is prepared by thin gold film deposition onto a metal
surface and by subsequent polymer layer formation, can be applied in sensor research and technology. 相似文献
7.
Occurrence of pharmaceuticals in river water and their elimination in a pilot-scale drinking water treatment plant 总被引:10,自引:0,他引:10
The occurrence of four beta blockers, one antiepileptic drug, one lipid regulator, four anti-inflammatories, and three fluoroquinolones was studied in a river receiving sewage effluents. All compounds but two of the fluoroquinolones were observed in the water above their limit of quantification concentrations. The highest concentrations (up to 107 ng L(-1)) of the compounds were measured during the winter months. The river water was passed to a pilot-scale drinking water treatment plant, and the elimination of the pharmaceuticals was followed during the treatment. The processes applied by the plant consisted of ferric salt coagulation, rapid sand filtration, ozonation, two-stage granular activated carbon filtration (GAC), and UV disinfection. Following the coagulation, sedimentation, and rapid sand filtration, the studied pharmaceuticals were found to be eliminated only by an average of 13%. An efficient elimination was found to take place during ozonation at an ozone dose of about 1 mg L(-1) (i.e., 0.2-0.4 mg of O3/ mg of TOC). Following this treatment, the concentrations of the pharmaceuticals dropped to below the quantification limits with the exception of ciprofloxacin. Atenolol, sotalol, and ciprofloxacin, the most hydrophilic of the studied pharmaceuticals, were not fully eliminated during the GAC filtrations. All in all, the treatment train was found to very effectively eliminate the pharmaceuticals from the rawwater. The only compound that was found to pass almost unaffected through all the treatment steps was ciprofloxacin. 相似文献
8.
Mottonen V.S. Piironen P. Raishanen A.V. 《Microwave and Wireless Components Letters, IEEE》2001,11(9):370-372
A new tunable waveguide backshort with low loss and reliable performance has been designed. Based on a fixed short and dielectric phase shifter, it has a simple structure which is easy to design and fabricate. These properties make it a sound alternative for millimeter- and submillimeter-wave applications. A W-band (75-110 GHz) backshort has been designed and tested showing excellent performance with a return loss of less than 0.21 dB 相似文献
9.
Although fatty acid composition is the most important attribute used to control oxidation stability, all edible oils are affected by lipid oxidation irrespective of whether they are highly unsaturated or not. The aim of the study was to compare the oxidation of rapeseed oil (RO) and butter oil (BO) triacylglycerols (TAGs) and their mixtures containing 10% or 20% of the other. Oxidation of the TAGs at 40°C was followed by formation of primary and secondary products. Statistical methods were used to interpret the data. The RO and BO TAGs and their mixtures began to oxidise without any induction periods. In the RO TAGs more hydroperoxides and p‐anisidine reactive compounds were formed than in the BO TAGs. The BO TAGs oxidised more than would be expected by their fatty acid composition. High susceptibility of BO TAGs to oxidation was caused by the easy breakdown of their hydroperoxides. Heptadienal and heptenal were specific products of oxidised RO TAGs and heptanal and nonenal of oxidised BO TAGs. Mixtures of RO and BO TAGs behaved according to which was dominant in the mixture. However, as little as 10% of RO or BO TAG introduced its specific oxidation products to the mixture. © 1999 Society of Chemical Industry 相似文献
10.
Although tocopherols are known to be the most important natural antioxidants in fats and oils, controversial findings of their effects have been made in different model systems. The aim of the experiment was to study the effects of α- and γ-tocopherol at the levels of 2–500 μg/g on the oxidation of purified butter oil triacylglycerols (BO TAGs) at 40°C in the dark for 16 days. Both of the tocopherols were effective antioxidants. Although BO TAGs without additions began to oxidize immediately, BO TAGs with tocopherols remained in the induction period throughout the experiment. The antioxidant strength of α-tocopherol was less than that of γ-tocopherol. More hydroperoxides were formed in BO TAGs with at least 100 μg/g α-tocopherol than with less α-tocopherol at the same time being much less than in BO TAGs without tocopherols. Moreover, as the formation of secondary oxidation products in BO TAGs with tocopherols was negligible, no pro-oxidative effect of tocopherols could be found. At low concentration (≤ 10 μg/g) γ-tocopherol was slightly less stable than α-tocopherol. 相似文献