A point about electron paramagnetic resonance detection of irradiated foodstuffs

This paper makes a point about the identification of irradiated foodstuffs by means of electron paramagnetic resonance (EPR) or electron spin resonance (ESR). EPR is the most accurate method for such routine applications since radicals are stabilised for a long time in all (or part of) foods that are in solid and dry states; consequently, EPR can be applied to meat and fish bones, fruit and relative products (from vegetal origin). More details are given for mollusc shells, such as oysters and mussels.     

Determination of butylated hydroxytoluene in food samples by high-performance liquid chromatography with ultraviolet detection and gas chromatography/mass spectrometry

A reversed-phase high-performance liquid chromatography (RP-HPLC) method was developed and compared with a gas chromatography/mass spectrometry (GC/MS) method for determining butylated hydroxytoluene (BHT) in foodstuffs as a result of migration from plastic packaging. Similar extraction procedures were used in both methods. BHT was quantitated using an external standard in the HPLC method and an internal standard in the GC/MS method. Both methods presented good linearity (r(2) > or = 0.9917) and low detection limits. Recoveries obtained with the HPLC method (chicken meat, 95.8%, and Gouda cheese, 83.9%) were better than with the GC/MS method (chicken meat, 85.6%, and Gouda cheese, 71.3%).     

Multi-frequency electron paramagnetic resonance study of irradiated human finger phalanxes

Electron paramagnetic resonance (EPR) is often used in dosimetry using biological samples such as teeth and bones. It is generally assumed that the radicals, formed after irradiation, are similar in both tissues as the mineral part of bone and tooth is carbonated hydroxyapatite. However, there is a lack of experimental evidence to support this assumption. The aim of the present study was to contribute to that field by studying powder and block samples of human finger phalanxes that were irradiated and analyzed by multi-frequency EPR. The results obtained from bones are different from the ones obtained in enamel by several respects: the ordering of the apatite crystallites is much smaller in bone, complicating the assignment of the observed CO2- radicals to a specific location, and one type of CO3(3-) radical was only found in enamel. Moreover, a major difference was found in the non-CO2- and non-CO3(3-) signals. The elucidation of the nature of these native signals (in bone and tooth enamel) still represents a big challenge.     

Overview of methods for the determination of trans fatty acids by gas chromatography, silver-ion thin-layer chromatography, silver-ion liquid chromatography, and gas chromatography/mass spectrometry

trans Isomers of naturally occurring cis-unsaturated fatty acids are produced when liquid vegetable oils or marine oils are partially hydrogenated to produce margarine, shortenings, and other hardened-fat products. Isomeric trans fatty acids are also formed in the intestinal tract of ruminants, and they appear in small amounts in dairy products and ruminant meat. Currently, satisfactory analyses for the fatty acid profiles of fats containing trans fatty acids are obtained by gas chromatography (GC) using capillary columns coated with highly polar cyanosilicone stationary phases. In capillary GC methods, the key limitation has been the incomplete separation of trans-monoenoic acid isomers from their cis isomers; however, recent reports have demonstrated that improvements in separation are attainable with the use of 100 m columns. In these columns, there is very little overlap of cis and trans isomers. More accurate trans fatty acid analyses can be obtained by coupling GC with either silver-nitrate thin-layer chromatography or silver-nitrate liquid chromatography.     

兔肉腥味物质的提取与鉴定

兔肉腥味（风味）物质与组织结合紧密，使用十二烷基硫酸钠（SDS）可使腥味物质解离释放。应用改进的NPT技术提得未去势与去势兔肉中腥味物质，经气－质联谱比较分析，初步确定中级醛类尤其己醛是兔肉腥味物质的主导成分；两种卤代烷烃（1－氯十二烷和1－溴十三烷）可能是构成兔肉特殊气味的重要成分。     

全氟和ω-H-全氟酰基过氧化物与C60的自由基加成反应——全氟和ω-H-全氟烷基化C60的合成

深入研究了C60与全氟酰基过氧化物的反应，通过变温EPR测试证实了此反应的 自由基加成机理．用色谱分析并结合产物的^19F NMR结构鉴定，首次发现由于加成 过程中发生的全氟烷基自由基的β—Scission，生成了新的氟烷基自由基，从而生 成了多种氟烷基化的C60．表面性能研究发现氟烷基化的C60具有优良的疏水、疏油 性．总之，利用C60与全氟酰基过氧化物的反应，成功地对C60进行了全氟烷基化修 饰．     

In-house validation of an improved sample extraction and clean-up method for GC determination of isomers of nervonic acid in meat products

An improved extraction and clean-up method for determination of brain-specific fatty acids, in particular lignoceric acid (C24:0) and the cis/ trans isomers of nervonic acid (15 c-t C24:1), in meat products has been developed. The method is based on isolation of the polar lipids of interest from the bulk lipids by solid-phase extraction. The fatty acids, derivatised to their fatty acid methyl esters, are quantified by GC in a DB5 column. Fresh meat samples were extracted by using a mixture of n-butanol:hexane (1:9) as solvent. The extract was loaded in a silica gel cartridge column previously equilibrated with hexane. The first fraction containing the major part of the fat was eluted with hexane while acetone and methanol allowed the elution of fatty acids bound to polar moieties such as nervonic and lignoceric acids. This second fraction containing the analyte was methylated and injected into the GC for quantification after addition octacosane (C(28)) as internal standard.     

基于脂肪酸差异的肉制品中猪源性成分鉴别方法的研究

建立了肉制品中脂肪酸的分析检测技术,通过分析脂肪酸含量、种类以及片段特征指纹图谱,实现了基于脂肪酸差异的肉制品中猪源性成分的鉴别。采用气相色谱法测定了大量肉制品,利用保留时间和质谱鉴定了36种脂肪酸成分,选取较为稳定的18种脂肪酸数据进行统计分析,确定不同油脂脂肪酸的差异,结合特征图谱,最终确定可用于鉴别猪源性成分的8种脂肪酸。该方法可用于确定肉制品中是否含有猪源性成分,方法简单、快速、成本低,辨别度较高,在猪源性成分鉴别中具有一定的应用前景。     

Catalytic reduction of NO to N2O by a designed heme copper center in myoglobin: implications for the role of metal ions

The effects of metal ions on the reduction of nitric oxide (NO) with a designed heme copper center in myoglobin (F43H/L29H sperm whale Mb, CuBMb) were investigated under reducing anaerobic conditions using UV-vis and EPR spectroscopic techniques as well as GC/MS. In the presence of Cu(I), catalytic reduction of NO to N2O by CuBMb was observed with turnover number of 2 mol NO.mol CuBMb-1.min-1, close to 3 mol NO.mol enzyme-1.min-1 reported for the ba3 oxidases from T. thermophilus. Formation of a His-heme-NO species was detected by UV-vis and EPR spectroscopy. In comparison to the EPR spectra of ferrous-CuBMb-NO in the absence of metal ions, the EPR spectra of ferrous-CuBMb-NO in the presence of Cu(I) showed less-resolved hyperfine splitting from the proximal histidine, probably due to weakening of the proximal His-heme bond. In the presence of Zn(II), formation of a five-coordinate ferrous-CuBMb-NO species, resulting from cleavage of the proximal heme Fe-His bond, was shown by UV-vis and EPR spectroscopic studies. The reduction of NO to N2O was not observed in the presence of Zn(II). Control experiments using wild-type myoglobin indicated no reduction of NO in the presence of either Cu(I) or Zn(II). These results suggest that both the identity and the oxidation state of the metal ion in the CuB center are important for NO reduction. A redox-active metal ion is required to deliver electrons, and a higher oxidation state is preferred to weaken the heme iron-proximal histidine toward a five-coordinate key intermediate in NO reduction.     

Application of the new EPR spin trap 1,1,3-trimethylisoindole N-oxide (TMINO) in trapping HO. and related biologically important radicals

The new EPR spin trap, 1,1,3-trimethylisoindole N-oxide (TMINO), very efficiently scavenges several Fenton-derived carbon- and oxygen-centred radicals including hydroxyl, formyl and alkyl radicals. The adducts display good stability and narrow EPR line-widths, allowing the detection of the expected radicals as well as two-dimensional (time-resolved) EPR experiments. Trapping experiments were also undertaken with superoxide radicals (giving no EPR signals) and nitric oxide (which gave strong EPR signals attributed to the action of higher oxides of nitrogen). The selectivity of TMINO towards HO. with respect to superoxide radicals demonstrates its potential as a useful spin-trap.     

Hydrocarbon contaminants of boiled shrimp and crab meat

Capillary GC and GC-MS have been used for the identification and quantitation of n-alkanes, naphthalenes, and alkylben-zenes among the volatile components of crab and shrimp meat.     

Qualitative and quantitative analysis of lipid extracts from rabbit meat by gas chromatography/mass spectrometry.

Analyses of lipid extracts from rabbit meat were carried out by gas chromatography/mass spectrometry (GC/mS) using both electron and chemical ionisation. Ten rabbit carcasses were randomly acquired on the market, from different farms; for each of them muscular tissues from hindleg and breast were analysed. The lipid fractions were extracted, separated and hydrolysed. The fatty acid fractions were derivatised by 2,2-dimethoxypropane. The GC/mS data obtained using electron ionisation (EI) did not allow the complete characterisation of the fatty acid fraction, and for this reason chemical ionisation (CI) was employed using acetonitrile as reactant gas. The data thus obtained show that, for both samples of rabbit tissue, the mean abundance ratio of plasma cholesterol lowering fatty acids and plasma cholesterol elevating fatty acids (PCL/PCE), taken as a parameter describing a desirable lipid uptake, is 2.2 +/- 0.3, significantly higher than the values reported for other meats (0.8-1. 8). These data, together with the high concentration of (n-6) fatty acids, provide a good indication of the high nutritional value of rabbit meat.     

全二维气相色谱在食品风味化学成分分析中的应用

食品风味是评价食品品质特征的重要指标。食品风味物质分析通常采用一维气相色谱或气相色谱-质谱联用法,但由于某些食品风味成分组成和基质复杂,无法用一维气相色谱将其完全分离。全二维气相色谱将分离机理不同而又相互独立的两根色谱柱以正交方式组合,显著提升了色谱分离能力和分析速度,可满足食品中风味化学成分的二次分离。该文综述了全二维气相色谱技术在未经二次加工的食用农产品(如水果、蔬菜和肉类)和经过二次加工的食品(如乳制品、饮品和调味品)中风味化学成分分析中的应用,展现了全二维气相色谱技术的特点,并为食品风味的解析提供参考。     

Chemical composition, olfactory evaluation and antimicrobial activity of selected essential oils and absolutes from Morocco

The chemical compositions of selected essential oils from North Africa, especially Morocco, of geranium, wild Moroccan chamomile and rosemary as well as absolutes of rose and geranium were determined using GC/FID and GC/MS. These oils and absolutes were tested concerning their antimicrobial activity against some food spoilage strains obtained from fresh milk and minced meat products, like sausages and pork fillet, in accordance with ISO testing procedures. Gram-positive (Bacillus cereus and Staphylococcus aureus) and Gram-negative (Escherichia coli, Salmonella abony and Pseudomonas aeruginosa) strains were used, as well as the yeast Candida albicans. Using a serial broth dilution method, all samples demonstrated weak antimicrobial activity against the Gram-negative bacteria and the yeast, compared with the activity towards the Gram-positive bacteria.     

Very high-field EPR study of glycyl radical enzymes

This work shows that very high-field EPR spectroscopy allows a rather accurate determination of the g-tensor of protein radicals, including C-centered ones, and thus may be used as a probe for distinguishing a tyrosyl-, a glycyl-, or a tryptophanyl-radical. In this paper, we report the first complete analysis of the g-tensor of glycyl radical enzymes (anaerobic ribonucleotide reductase, pyruvate formate lyase, and benzylsuccinate synthase), thus providing new information on their EPR properties. Because the g-anisotropy is small, the complete resolution of the g-tensor could be only obtained at very high field (18.8 T).     

Effect of Different Heat Treatments on the Quality and Flavor Compounds of Black Tibetan Sheep Meat by HS-GC-IMS Coupled with Multivariate Analysis

There are limited reports about the effect of different heat treatments on the quality and flavor of Black Tibetan sheep meat. The current study examined the effect of pan-frying, deep-frying, baking, and boiling treatment on the quality of Black Tibetan sheep meat; the amino acid, fatty acid, and volatile flavor compounds (VFCs) were investigated by a texture analyzer, ultra-high-performance liquid chromatography (UHPLC), gas chromatography (GC), and headspace-gas chromatography-ion mobility (HS-GC-IMS). The key VFCs were identified through orthogonal partial least squares discrimination analysis (OPLS-DA), and variable importance projection (VIP) values. In addition, Pearson’s correlations between meat quality parameters and key VFCs were examined. The sensory scores, including texture, color, and appearance, of baked and pan-fried meat were higher than those of deep-fried and boiled meat. The protein (40.47%) and amino acid (62.93 µmol/g) contents were the highest in pan-fried meat (p < 0.05). Additionally, it contained the highest amounts of monounsaturated and polyunsaturated fatty acids, such as oleic, linoleic, and α-linolenic acids (p < 0.05). Meanwhile, pan-fried and deep-fried meat had higher amounts of VFCs than baked meat. The OPLS-DA similarity and fingerprinting analyses revealed significant differences between the three heat treatment methods. Aldehydes were the key aroma compounds in pan-fried meat. Importantly, 3-methylbutyraldehyde and 2-heptanone contents were positively correlated with eicosenoic, oleic, isooleic, linoleic, α-Linolenic, and eicosadiene acids (p < 0.05). To sum up, pan-fried Black Tibetan sheep meat had the best edible, nutritional, and flavor quality.     

Filling factor of a paramagnetic sample in a rectangular cavity: theory and application

A computational method is presented for calculating the filling factor of an electron paramagnetic resonance (EPR) tube in a rectangular TE102 cavity. The algorithm employs the conventional finite element method. In addition to the filling factor, the algorithm allows to calculate the quality factor and the reflection coefficient of the loaded cavity. This method allows calculating very accurately the EPR signal intensities from which the spin concentration of paramagnetic samples can be determined. A comparison between the predicted EPR signal intensities to several experimental results was found to be satisfactory. The method also allows optimizing the EPR tube dimensions and its glass quality to improve measurement sensitivity.     

Identification of unknown compounds on the basis of retention index data in comprehensive two-dimensional gas chromatography

The identification of unknown compounds in complex samples is very difficult. Comprehensive two-dimensional gas chromatography (GC x GC) provides very good resolution and improved identification reliability. Mass spectrometry is a powerful identification tool and retention index data are another good approach to this end. In this study, a second-order polynomial was used to calculate retention index data based on n-alkanes beyond the region of the 'isovolatile' curve in GC x GC, and the results in the 2nd dimension were validated by using the same stationary phase column in one-dimensional GC. To test the usefulness of the method, volatile compounds in a tobacco leaf extract fraction were analyzed using GC x GC, and 60 compounds were identified on the basis of their retention indices.     

Method for the analysis of thyreostats in meat tissue using gas chromatography with nitrogen phosphorus detection and tandem mass spectrometric confirmation

An analytical method not requiring a mercury column cleanup step is described for the isolation and detection of four thyreostatic agents in meat tissue. The use of these growth promotants in livestock has been banned by regulatory agencies. The meat tissue is homogenized with acetonitrile-water, centrifuged, and the supernatant is partitioned with petroleum ether. The acetonitrile-water is concentrated and then passed through a silica-gel column. The solvent is then removed and the residue derivatized with N-methyl-N-(trimethylsilyl)-trifluoroacetamide. The total amount of organic solvent used for the analysis is merely 35 mL. The derivatized thyreostats are detected and quantitated by gas chromatography (GC) equipped with a nitrogen-phosphorus detector. Percent recoveries from fortified meat tissue (n = 6) at the 0.1-microg/g (parts per million) level are 93.5 +/- 2.9 for 2-thiouracil, 90.3 +/- 3.0 for tapazole, 87.5 +/- 2.9 for 6-methyl-2-thiouracil, and 85.1 +/- 5.8 for 6-n-propyl-2-thiouracil. For the confirmation of analyte identities, GC-tandem mass spectrometry with an ion-trap instrument is used. The estimated minimum level for a reliable measurement is 0.050 microg/g in meat tissue.     

Single-wall carbon nanotubes and peapods investigated by EPR

Single-wall carbon nanotubes (SWNT) prepared by the "super growth" method developed recently exhibit electron paramagnetic resonance (EPR) signals, which can be attributed to itinerant spins. EPR results indicate very low defect and catalyst concentrations in this superior material. Under these conditions EPR can be used to study details of charge transport properties over a wide temperature range, although the material is still very "heterogeneous" with respect to tube diameter and chirality. Non-resonant microwave absorption in the temperature range below 20 K is indicative for the opening of a small gap at the Fermi energy for tubes of metallic character, which is indicative for a transition into a superconducting state. Using SWNT filled partially with an endohedral spin probe like N@C(60), such "peapods" can be investigated "from the inside". Continuous-wave (cw) and pulsed EPR was used to investigate localization dynamics within the tubes or to check for interaction with itinerant electrons. Using SWNT grown by different methods, the dominant influence of tube diameter on fullerene dynamics was revealed by temperature dependent pulsed EPR experiments. These differences can be correlated with the interactions between the endohedral observer spin and spins on the SWNT.