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1.
A sensitive method is described for determining dicamba at low micrograms/L levels in ground waters by capillary column gas chromatography with electron-capture detection (GC-EC); compound identity is confirmed by gas chromatography-mass spectrometry (GC-MS) using selected ion monitoring. Dicamba residue is hydrolyzed in KOH to form the potassium salt. The sample is then extracted with ethyl ether which is discarded. The aqueous phase is acidified to pH less than 1 and extracted twice with ethyl ether. The combined ethyl ether extracts are concentrated, and the residue is methylated using diazomethane to form the corresponding dicamba ester. The derivatized sample is cleaned up on a deactivated silica gel column. The methylated dicamba is separated on an SE-30 capillary column and quantitated by electron-capture or mass spectrometric detection. Average recoveries (X +/- SD) for ground water samples fortified with 0.40 microgram/L of dicamba are 86 +/- 5% by GC-EC and 97 +/- 7% by GC-MS detections. The EDL (estimated detection limit) for this method is 0.1 microgram dicamba/L water (ppb).  相似文献   

2.
A method for the quantitative determination of monoethylene glycol (MEG) and diethylene glycol (DEG) in chocolate is described. The procedure involves dissolving the chocolate in hot water, defatting with hexane, removing sugars by precipitation, and analyzing as trimethylsilyl (TMS) ether derivatives by capillary gas chromatography. The use of butan-1,4-diol as an internal standard corrects for recovery, which is between 50 and 60%, to give a relative standard deviation of 10-11% for the determination of both glycols at the level of 50 mg/kg. The presence of MEG and DEG in chocolate is confirmed by full scanning gas chromatography/mass spectrometry of the TMS derivatives.  相似文献   

3.
A new method has been developed for measuring the D/H ratio of the nonexchangeable sites of citric acid by isotope ratio mass spectrometry (IRMS). Pure citric acid is transformed into its calcium salt and subsequently analyzed by pyrolysis-IRMS. The citric acid isolated from authentic fruit juices (citrus, pineapple, and red fruits) systematically shows higher D/H values than its nonfruit counterpart produced by fermentation of various sugar sources. The discrimination obtained with this simplified method is similar to that obtained previously by applying site specific isotopic fractionation-nuclear magnetic resonance (SNIF-NMR) to an ester derivative of citric acid. The combination of carbon 13 and deuterium measurements of extracted citric acid is proposed as a routine method for an optimum detection of exogenous citric acid in all kinds of fruit juices.  相似文献   

4.
The suitability of a one-step derivatization procedure using N-methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide for the simultaneous assay of 22 free amino acids and its application for their analysis in six animal source foods (pork, dry cured ham, chicken stock, fresh cheese, ripened cheese, and dry salted sardine) by GC-MS were studied. All 22 free amino acid derivatives were correctly detected and resolved. Reproducibility (%RSD) of the method was in the range of 1.9-12.2%. Detection and quantitation limits of the analytical procedure ranged from 0.01 to 0.46 mg/100 g dry weight and from 0.02 to 1.55 mg/100 g dry weight, respectively. The calibration curves were linear within the range 0.1-15.0 mg/100 g with correlation coefficient values (R(2)) from 0.9891 to 0.9983. All analyzed food products showed free amino acid contents similar to those found in the scientific literature. The proposed GC-MS method for the determination of free amino acids in animal source food can be used in routine for both analytical and research purposes.  相似文献   

5.
The effect of tartaric acid and other organic acids on alcoholic fermentation was studied. Organic acids in media with high sugar concentrations and ammonium as the sole nitrogen source had an enormous impact on Saccharomyces cerevisiae metabolism during alcoholic fermentation. The main effect on yeast metabolism was the quick acidification of the media in the absence of organic acids. All of the organic acids used in this study (tartaric, malic, citric, and succinic acids) showed a buffering capacity, but not all of the acids had the same one. However, the results suggested that buffering should not be considered the only effect of organic acids on yeast metabolism. Nitrogen source also had a great influence on media pH. Ammonium consumption by yeasts produced a greater acidification of the media than when amino acids were used.  相似文献   

6.
植物乳杆菌发酵不同果蔬汁风味品质研究   总被引：2，自引：0，他引：2  
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7.
A study of the phenolic and volatile composition of wines produced from the white cultivar Muscat lefko from the island of Samos was conducted. Dry, fortified, naturally sweet wines and mistelles (aged and nonaged) have been studied. The phenolic components (flavan-3-ols, hydroxycinnamates, and flavonols) were measured by high-performance liquid chromatography after solid phase extraction (SPE). The terpenes (free and glycosidically linked) were determined by the use of gas chromatography-mass spectrometry (GC-MS) after SPE. The fermentation aroma components were analyzed by GC-MS after liquid-liquid extraction. It was found that the dry wines contained lower amounts of most of the phenolics and higher quantities of terpenes and fermentation aroma compounds than the sweet wines. The aged mistelle wines contained lower levels of coutaric and caftaric acids, higher concentrations of the free acids, and markedly fewer free and bound terpenes and fermentation aroma components compared to the other sweet wines. The naturally sweet wine contained relatively increased amounts of phenolics, 2,3-butanediol, and glycosidically linked terpenes.  相似文献   

8.
Methods to refine the assessment of exposure of wild birds and mammals to pesticides required measurement of pesticide residues in very small samples of their diets. Sample sizes were in the 1-100 mg range, and the target residue for measurement was 0.01 mg/kg. Gas chromatography-mass spectrometry (GC-MS) with large volume injection was compared with the use of an accelerator mass spectrometer (AMS) to measure residues of pesticide labeled at near-background levels with carbon-14. The GC-MS method was able to detect residues down to 0.1 ng per item of diet, and the AMS detected the radiolabel down to 1 mBq (0.06 disintegration per minute, 1 ng of pesticide at the specific activity used) per sample. The target residue level was achieved by the GC-MS method for samples down to 10 mg. The GC method appeared to be best suited to monitoring residues in field studies, and the AMS shows great potential for use in laboratory experiments concerning pesticide degradation.  相似文献   

9.
The chemical composition of the lipophilic extracts of unripe pulp and peel of banana fruit 'Dwarf Cavendish' was studied by gas chromatography-mass spectrometry. Fatty acids, sterols, and steryl esters are the major families of lipophilic components present in banana tissues, followed by diacylglycerols, steryl glucosides, long chain fatty alcohols, and aromatic compounds. Fatty acids are more abundant in the banana pulp (29-90% of the total amount of lipophilic extract), with linoleic, linolenic, and oleic acids as the major compounds of this family. In banana peel, sterols represent about 49-71% of the lipophilic extract with two triterpenic ketones (31-norcyclolaudenone and cycloeucalenone) as the major components. The detection of high amounts of steryl esters (469-24405 mg/kg) and diacylglycerols (119-878 mg/kg), mainly present in the banana peel extract, explains the increase in the abundance of fatty acids and sterols after alkaline hydrolysis. Several steryl glucosides were also found in significative amounts (273-888 mg/kg), particularly in banana pulp (888 mg/kg). The high content of sterols (and their derivatives) in the 'Dwarf Cavendish' fruit can open new strategies for the valorization of the banana residues as a potential source of high-value phytochemicals with nutraceutical and functional food additive applications.  相似文献   

10.
2- and 3-hydroxy fatty acids (2- and 3-OH-FAs) are bioactive substances reported in sphingolipids and bacteria. Little is known of their occurrence in food. For this reason, a method suitable for the determination of OH-FAs at trace levels in bovine milk fat was developed. OH-FAs (and conventional fatty acids in samples) were converted into methyl esters and the hydroxyl group was derivatized with pentafluorobenzoyl (PFBO) chloride to give PFBO- O-FA methyl esters. These derivatives with strong electron affinity were determined by gas chromatography interfaced to mass spectrometry using electron-capture negative ion in the selected ion monitoring mode (GC/ECNI-MS-SIM). This method proved to be highly sensitive and selective for PFBO-O-FA methyl esters. For the analysis of samples, two internal standards were used. For this purpose, 9,10-dideutero-2-OH-18:0 methyl ester (ISTD-1) from 2-OH-18:1(9 c) methyl ester as well as the ethyl ester of 3-PFBO-O-12:0 (ISTD-2) was synthesized. ISTD-1 served as a recovery standard whereas ISTD-2 was used for GC/MS measurements. The whole-sample cleanup consisted of accelerated solvent extraction of dry bovine milk, addition of ISTD 1, saponification, conversion of fatty acids into methyl esters by use of boron trifluoride, separation of the methyl esters of OH-FAs from nonsubstituted FAs on activated silica, conversion of OH-FAs methyl esters into PFBO-O-FA methyl esters, addition of ISTD-2, and measurement by GC/ECNI-MS-SIM. By this method, ten OH-FAs were quantified in bovine milk fat with high precision in the range from 0.02 +/- 0.00 to 4.49 +/- 0.29 mg/100 g of milk fat.  相似文献   

11.
Agave plants utilize crassulacean acid metabolism (CAM) for CO(2) fixation. Fructans are the principal photosynthetic products generated by agave plants. These carbohydrates are fructose-bound polymers frequently with a single glucose moiety. Agave tequilana Weber var. azul is an economically important CAM species not only because it is the sole plant allowed for tequila production but because it is a potential source of prebiotics. Because of the large amounts of carbohydrates in A. tequilana, in this study the molecular structures of its fructans were determined by fructan derivatization for linkage analysis coupled with gas chromatography-mass spectrometry (GC-MS), nuclear magnetic resonance (NMR), and matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF-MS). Fructans were extracted from 8-year-old A. tequilana plants. The linkage types present in fructans from A. tequilana were determined by permethylation followed by reductive cleavage, acetylation, and finally GC-MS analysis. Analysis of the degree of polymerization (DP) estimated by (1)H NMR integration and (13)C NMR and confirmed by MALDI-TOF-MS showed a wide DP ranging from 3 to 29 units. All of the analyses performed demonstrated that fructans from A. tequilana consist of a complex mixture of fructooligosaccharides containing principally beta(2 --> 1) linkages, but also beta(2 --> 6) and branch moieties were observed. Finally, it can be stated that fructans from A. tequilana Weber var. azul are not an inulin type as previously thought.  相似文献   

12.
The development of an analytical method using 1H nuclear magnetic resonance (1H NMR) spectrometry to monitor cupuassu (Theobroma grandiflorum Spreng) bean fermentation, drying, and roasting processes is reported. The analysis of organic acids and alcohols of crude water extracts of cupuassu ground kernels were monitored by HPLC and 1H NMR spectroscopy. The residual protein signals caused deleterious effects on acid and alcohol quantifications. Therefore, the analytical procedures were optimized by sample cleanup and water suppression pulse sequences in order to obtain compatible data using HPLC and 1H NMR. The quantification of lactic acid, acetic acid, and 2,3-butanediol by NMR is 5- to 10-fold faster than by HPLC, with the advantage of providing the identification of several chemical species in a single experiment. Application of these analytical conditions to some cupuassu samples revealed that this methodology can be applied to the quality profiles of fermentation and roasting processes.  相似文献   

13.
Hot dogs contain apparent N-nitroso compounds (ANC) and ANC precursors (ANCP). ANCP purification was followed by nitrosation, sulfamic acid treatment, and analysis for ANC. Aqueous hot dog extracts were adsorbed on silica gel, which was eluted with MeCN and MeOH. The MeOH eluate was adsorbed on cation exchange resin (H+ form) and eluted with NH4OH. Eluted ANCP traveled at moderate speeds in high-performance liquid chromatography (HPLC) on amino and Pb2+ columns. Gas chromatography-mass spectrometry (GC-MS) of trimethylsilyl (TMS) derivatives of crude water extract indicated the presence of glycerol, phosphate, lactic acid, and two monosaccharides. GC-MS of TMS derivatives of Pb2+ column HPLC eluates indicated that ANCP included 1-deoxy-N-1-glucosyl glycine. The nitrosated NH4OH eluate showed 4x background mutagenic activity for Salmonella typhimurium TA-100. Un-nitrosated fractions showed 2x background activity. Although tryptophan nitrosation gave 88% ANC yield, tryptophan is probably not a major ANCP in hot dogs. Hot dog patties prepared with or without sucrose or glucose showed similar ANC and ANCP levels. We discuss possible implications of these findings for the etiology of colon cancer.  相似文献   

14.
The monomeric composition of suberin extracts obtained by gradual alkaline methanolysis of Quercus suber cork was determined by gas chromatography-mass spectrometry (GC-MS). Results show that 1-alkanols and alkanoic and alpha,omega-alkanedioic acids are preferentially removed upon mild alkaline conditions, whereas mid-chain-modified omega-hydroxyalkanoic acids are preferentially removed under stronger alkaline conditions. Saturated omega-hydroxyalkanoic acids are found to be abundant in all suberin extracts. These results are consistent with two distinct suberin fractions with different locations in cork cell walls and/or esterification degrees. It is proposed that these fractions correlate with the two main suberin peaks in the solid state (13)C NMR spectra of cork and suberin extracts. Quantitative GC-MS analysis showed that suberin monomers comprise approximately 30% (w/w) of the suberin extracts, the remaining comprising nonvolatile structures with high M(n) values, as measured by vapor pressure osmometry. The presence of a large fraction of high molecular weight aliphatic structures in suberin extracts is supported by the corresponding NMR spectra.  相似文献   

15.
Quantitative NMR can be used to monitor several processes that take place in the transformation of the must of wine grapes. The study described here focused attention on monitoring of the malic and lactic acid levels during the alcoholic and malolactic fermentation processes. The method allows the simultaneous quantification of both acids through a range of 1-3.2 mmol/L. The effectiveness of each process was assessed and compared by carrying out precise analyses using enzymatic methods.  相似文献   

16.
采用间歇法(batch method)模拟研究醋酸-醋酸铵缓冲体系中柠檬酸对高岭石的溶解特征。结果表明:反应液中Al、Si浓度随柠檬酸浓度提高、反应液pH降低及反应时间的推移而增加;且低浓度柠檬酸(1mmol L-1)时,随着酸度的升高,配体促进溶解速率(RL)减小;高浓度柠檬酸(≥5mmol L-1)时,随着酸度的升高,配体促进溶解速率(RL)增加,但增幅随pH的降低而大幅减弱;且随着酸度的升高,配体对高岭石溶解的贡献相对减弱,但相对于质子,本试验柠檬酸浓度及酸度范围内,其对高岭石溶解的贡献仍是主要的。  相似文献   

17.
Organic acid analysis plays a fundamental role in the testing of authenticity of fruit juices. Analytical methods used routinely for organic acids suffer from poor reproducibility, often give false positives/negatives for tartaric acid, and do not offer the possibility of analyte confirmation. There are conflicting reports in the literature on the presence/absence of tartaric acid in pomegranate juice, a potential indicator of adulteration with grape juice. In this work, a method based on stable isotope dilution liquid chromatography-tandem mass spectrometry is described for citric, malic, quinic, and tartaric acid in fruit juices. Validation data including precision and recovery in six types of juice are presented. Tartaric and quinic acids were confirmed in pomegranate juice at concentrations of 1-5 and ～1 mg/L, respectively. These concentrations are much lower than those resulting from adulteration with grape juice and apple juice, respectively, at the 5% level. A separate method for isocitric acid in orange juice based on the single standard addition method is also described.  相似文献   

18.
This paper describes a comparative study of the gravimetric versus hydrolysis/derivatization/gas chromatography-mass spectrometry determination of fat in infant formula. Fat was extracted using supercritical carbon dioxide modified with a small amount of ethanol, the extract was weighed, and the total fat was determined gravimetrically. Subsequently, another sample of the supercritical fluid fat extract was hydrolyzed to yield free fatty acids, which were converted to their methyl ester derivatives (FAMEs). Quantification was performed by GC-MS. NIST Standard Reference Material (SRM-1846) was used to validate both fat determination methods. Results showed that the gravimetric average percent fat was 26.86%, whereas the GC-MS method yielded 24.64%. Some peaks were detected in the ion chromatogram from the GC-MS that were identified as nonfatty acids such as aldehydes, which may account for the higher percentage fat measured as weight of extract rather than measured as FAMEs expressed as triglycerides.  相似文献   

19.
A fast, one-step gas chromatographic method was developed to analyze trimethylsilyl (TMS) derivatives of sugars, fruit acids, and ascorbic acid in sea buckthorn (Hippoha? rhamnoides L.) berries. The method was applied to berry press juice of sea buckthorn of different origins grown in Finland during the 2003 and 2004 seasons. The method gave reliable results for D-fructose, D-glucose, ethyl-D-glucose, and malic, quinic, and ascorbic acids, which are the major sugars and acids in sea buckthorn juice. For the first time in sea buckthorn and evidently in any berry, the presence of ethyl beta-D-glucopyranoside is reported. The structure of ethyl glucose was verified by high-performance liquid chromatography (HPLC), gas chromatography (GC), MS, and NMR analyses of both the isolated and the synthesized compounds. In the GC method, vitamin C was analyzed as ascorbic acid only, and dehydroascorbic acid was thus not taken into account.  相似文献   

20.
A method using gas chromatography/electron ionization-mass spectrometry (GC/EI-MS) in the selected ion monitoring (SIM) mode was developed for the analysis of fatty acids as methyl esters (FAMEs) in order to determine their percentage contribution to the fatty acid profile in food. In the GC/EI-MS-SIM mode, saturated fatty acids were determined with m/z 87, monoenoic fatty acids were determined with m/z 74, and polyenoic fatty acids were determined via the sum of m/z 79 and m/z 81. The ratios of these fragment ions and the GC retention data provided additional information for tentative structural assignments. The 28 FAME standards tested provided similar results for the novel GC/EI-MS-SIM method and GC/EI-MS in the full scan mode, both of which were slightly worse than GC/flame ionization detection (FID). Analysis of sunflower oil, suet, and cod liver oil verified that both major and minor fatty acids (20-60% and down to 0.001% contribution to the fatty acid pattern) were determined with sufficient quality that justifies application of the GC/EI-MS-SIM method for the analysis of food samples. Furthermore, the method was approximately 20- or approximately 10-fold more sensitive than GC/EI-MS in the full scan mode or GC/FID, respectively. The method is suited for both quantitative purposes and fatty acid identification in samples where only low amounts of lipids are available.  相似文献   

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