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1.
J Agric Food Chem ; 54(13): 4855-60, 2006 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-16787039

RESUMO

The flavonoid composition of immature leaves of pak choi [Brassica rapa L. ssp. chinensis L. (Hanelt.)] was investigated. Flavonol aglycone content was measured in 11 pak choi varieties, indicating significant differences (P < 0.05) in content between varieties and relatively high contents of kaempferol and isorhamnetin. Levels of quercetin ranged from 3.2 to 6.1 mg/100 g of dry weight (DW), whereas levels of isorhamnetin and kaempferol were significantly higher (8.1-35.1 and 36.0-102.6 mg/100 g of DW, respectively). A large number of glycoside and hydroxycinnamic acid derivatives of quercetin, kaempferol, and isorhamnetin were identified in cv. 'Shanghai' by LC/UV-DAD/ESI-MS/MS. The UV-DAD data allowed identification of hydroxycinnamic acid derivatives, but detailed MS/MS fragmentations were required for the structure elucidation. Pak choi could be a potentially important source of dietary flavonols, in particular, kaempferol and isorhamnetin.


Assuntos
Brassica rapa/química , Cromatografia Líquida de Alta Pressão , Flavonóis/análise , Espectrometria de Massas , Folhas de Planta/química , Ácidos Cumáricos/análise , Glicosídeos/análise , Quempferóis/análise , Quercetina/análise
2.
J Anal Toxicol ; 30(3): 178-86, 2006 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-16803652

RESUMO

A new analytical procedure was developed for the quantitation of nonsmoker salivary cotinine. Small volumes of saliva were diluted with water, fortified with cotinine-d3 (internal standard), then passed through small extraction columns. The analyte and internal standard were eluted with 0.1% (v/v) acetic acid/acetonitrile. Aliquots of each extract were analyzed directly, without chromatographic separation, using chip-based (NanoMate) nanospray tandem mass spectrometry. The calculated detection limit was 0.49 ng cotinine/mL saliva. This method was used to quantify salivary cotinine collected from nonsmoking human subjects living in one of three environmental tobacco smoke (ETS) exposure categories or "cells": 1. smoking home/smoking workplace; 2. smoking home/nonsmoking workplace; and 3. nonsmoking home/smoking workplace. Samples were collected during five sequential days, including Saturday, as part of a larger study to evaluate potential variability in exposure to ETS. Salivary cotinine measurements were made for the purpose of excluding misclassified smokers and for comparison with known levels of exposure to airborne nicotine in each exposure category. The concentrations observed were consistent with those reported from other large studies reported elsewhere. A non-parametric statistical test was applied to the data within each cell. No statistically significant differences were found between the mean cotinine concentrations collected on a weekday as compared to those collected on a weekend day. When the non-parametric test was applied to the three cells, a statistically significant difference was observed between cell 1 compared to cells 2 and 3. The salivary cotinine concentrations were thus statistically invariant over a five-day exposure period, and they were greatest under the conditions of smoking home and smoking workplace.


Assuntos
Cotinina/análise , Saliva/química , Poluição por Fumaça de Tabaco , Monitoramento Ambiental , Habitação , Humanos , Fumar , Espectrometria de Massas por Ionização por Electrospray , Local de Trabalho
3.
J Food Prot ; 78(12): 2150-5, 2015 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-26613909

RESUMO

Minor shoot injury significantly (P < 0.05) increased the level at which Salmonella enterica serovar Sofia persisted on cos lettuce in the greenhouse. Initial mean counts of the Salmonella on the injured and uninjured cos lettuce were on the order of 6 log CFU/g. After 3 days, the mean count decreased to 4.8 log CFU/g on the injured plants compared with the significantly (P < 0.05) smaller count of 3.4 log CFU/g on the uninjured plants. By the end of the 3-week experiment, the count from the injured plants was 2.9 log CFU/g compared with a count of below the level of detection from the uninjured plants. A similar pattern of bacterial persistence was observed on injured versus uninjured plants by using Listeria innocua on cos lettuce and S. enterica serovar Sofia on chive. The findings reaffirm earlier results with Escherichia coli and increase the impetus to avoid shoot injury during the production of cos lettuce and chive, if bacteria of food safety concern are present.


Assuntos
Cebolinha-Francesa/microbiologia , Lactuca/microbiologia , Listeria/crescimento & desenvolvimento , Brotos de Planta/microbiologia , Salmonella enterica/crescimento & desenvolvimento , Cebolinha-Francesa/crescimento & desenvolvimento , Microbiologia de Alimentos , Lactuca/crescimento & desenvolvimento , Brotos de Planta/crescimento & desenvolvimento , Sorogrupo
4.
Bioresour Technol ; 179: 202-210, 2015 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-25545089

RESUMO

Previous studies defined easy and difficult to hydrolyze fractions of hemicellulose that may result from bonds among cellulose, hemicellulose, and lignin. To understand how such bonds affect hydrolysis, Populus trichocarpa × Populus deltoides, holocellulose isolated from P. trichocarpa × P. deltoides and birchwood xylan were subjected to hydrothermal flow-through pretreatment. Samples were characterized by glycome profiling, HPLC, and UPLC-MS. Glycome profiling revealed steady fragmentation and removal of glycans from solids during hydrolysis. The extent of polysaccharide fragmentation, hydrolysis rate, and total xylose yield were lowest for P. trichocarpa × P. deltoides and greatest for birchwood xylan. Comparison of results from P. trichocarpa × P. deltoides and holocellulose suggested that lignin-carbohydrate complexes reduce hydrolysis rates and limit release of large xylooligomers. Smaller differences between results with holocellulose and birchwood xylan suggest xylan-cellulose hydrogen bonds limited hydrolysis, but to a lesser extent. These findings imply cell wall structure strongly influences hydrolysis.


Assuntos
Biotecnologia/métodos , Cruzamentos Genéticos , Populus/metabolismo , Temperatura , Água/farmacologia , Xilanos/metabolismo , Celulose/isolamento & purificação , Cromatografia Líquida de Alta Pressão , Glucose/metabolismo , Glicômica , Hidrólise/efeitos dos fármacos , Lignina/isolamento & purificação , Espectrometria de Massas , Polimerização/efeitos dos fármacos , Solventes/química , Xilose/metabolismo
5.
J Chromatogr A ; 964(1-2): 21-33, 2002 Jul 26.
Artigo em Inglês | MEDLINE | ID: mdl-12198850

RESUMO

A rapid, sensitive, convenient, and highly quality-assured method is presented for the determination of 19 organochlorine pesticides (OCPs) in small samples (10 ml) of ground water. Samples are initially fortified with 2,4,5,6-tetrachloro-m-xylene (surrogate) and decachlorobiphenyl (retention time marker), then extracted with a 30-micron thickness polydimethylsiloxane solid-phase microextraction fiber. The analytes collected are thermally desorbed in a heated gas chromatographic inlet, separated using independent fused-silica capillary columns ("primary" and "confirmatory"), and detected using electron-capture detection. Two independent statistical procedures were used to evaluate the detection limits, which typically range between 10 and 40 ng l-1, for these analytes. Method performance was also evaluated using two additional protocols employing "performance evaluation" samples, in which authentic ground water samples were fortified to ca. 100 ng l-1 in each of at least six OCPs. The method satisfies additional strict criteria based on uniformity of fiber performance and minimal degradation of the thermally-sensitive analytes endrin and DDT.


Assuntos
Cromatografia Gasosa/métodos , Hidrocarbonetos Clorados , Inseticidas/análise , Poluentes Químicos da Água/análise , Calibragem , Controle de Qualidade , Padrões de Referência , Sensibilidade e Especificidade
6.
J Chromatogr A ; 972(2): 183-94, 2002 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-12416876

RESUMO

A rapid, sensitive, and convenient method is presented for the determination of atrazine and four organophosphorus pesticides (OPP) in small (10 ml) samples of ground water. Samples are initially fortified with ethion (internal standard), then extracted without organic solvent using a 65-microm thickness polydimethylsiloxane/divinylbenzene (PDMS-DVB) solid-phase microextraction (SPME) fiber. The analytes collected are thermally desorbed in a heated gas chromatographic inlet, separated using a fused-silica capillary column, and detected using a mass selective detector in its selected-ion monitoring (SIM) mode. Two independent statistical procedures were used to evaluate the detection limits, which typically range between 2 and 8 microg l(-1) for these analytes. Method performance was also evaluated using "performance evaluation" samples, in which clean authentic ground waters were fortified to known concentrations with at least two of the analytes of interest. Sample-to-sample analysis time is approximately 30 min, making the new method ideal for "quick turn" determinations.


Assuntos
Atrazina/análise , Cromatografia Gasosa/métodos , Herbicidas/análise , Inseticidas/análise , Compostos Organofosforados , Poluentes Químicos da Água/análise , Sensibilidade e Especificidade
7.
J Agric Food Chem ; 50(25): 7386-91, 2002 Dec 04.
Artigo em Inglês | MEDLINE | ID: mdl-12452663

RESUMO

The effects of post-harvest and packaging treatments on glucoraphanin (4-methylsulfinylbutyl glucosinolate), the glucosinolate precursor of anticancer isothiocyanate sulforaphane [4-methylsulfinylbutyl isothiocyanate], were examined in broccoli (Brassica oleracea var. italica) during storage times. The results showed that at 20 degrees C, 55% loss of glucoraphanin concentration occurred in broccoli stored in open boxes during the first 3 days of the treatment and 56% loss was found in broccoli stored in plastic bags by day 7. Under both air and controlled atmosphere (CA) storage, glucoraphanin concentration appeared to fluctuate slightly during 25 days of storage and the concentrations under CA was significantly higher than those stored under air treatment. In modified atmosphere packaging (MAP) treatments, glucoraphanin concentration in air control packaging decreased significantly whereas there were no significant changes in glucoraphanin concentration in MAP with no holes at 4 degrees C and two microholes at 20 degrees C for up to 10 days. Decreases in glucoraphanin concentration occurred when the broccoli heads deteriorated. In the present study, the best method for preserving glucoraphanin concentration in broccoli heads after harvest was storage of broccoli in MAP and refrigeration at 4 degrees C. This condition maintained the glucoraphanin concentration for at least 10 days and also maintained the visual quality of the broccoli heads.


Assuntos
Brassica/química , Embalagem de Alimentos , Glucose/análogos & derivados , Glucose/análise , Imidoésteres/análise , Cromatografia Líquida de Alta Pressão , Temperatura Baixa , Cor , Manipulação de Alimentos , Conservação de Alimentos/métodos , Glucosinolatos , Umidade , Oximas , Sulfóxidos , Fatores de Tempo
8.
J Air Waste Manag Assoc ; 54(2): 229-41, 2004 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-14977324

RESUMO

Protocols have been developed and applied for the generation of aerosols that are likely to be comparable to those encountered in field settings for the calibration of easily transportable/portable real-time particle monitors. Aerosols generated were simulated environmental tobacco smoke, cedar wood smoke, cooking oil fumes, and propane stove particles. The time-integrated responses of three nephelometers and a monitor for particle-bound polynuclear aromatic hydrocarbons (PAH) were compared with gravimetric respirable suspended particulate matter (RSP) in a controlled-atmosphere chamber. In general, the monitor responses increased linearly with increasing mass concentration. However, the two monitors that reported mass per volume concentrations tended to overreport the actual RSP concentrations by factors up to 4.4. The real-time PAH monitor did not respond to cooking oil fumes, indicative of little PAH being present in the aerosol. One of the monitors that has been used in a variety of studies reported in the literature (DustTrak) was collocated with gravimetric RSP samplers in several hospitality venues in the Louisville, KY, area. Field studies indicated that the units overreported actual RSP concentrations by factors of 2.6-3.1, depending on whether the sampling was conducted in the nonsmoking or smoking sections of the facilities.


Assuntos
Aerossóis/análise , Poluição do Ar em Ambientes Fechados/análise , Monitoramento Ambiental/métodos , Calibragem , Monitoramento Ambiental/instrumentação , Tamanho da Partícula , Reprodutibilidade dos Testes , Fatores de Tempo
9.
J Forensic Sci ; 57(1): 75-9, 2012 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-22040310

RESUMO

Sodium and potassium cyanide are highly toxic, produced in large amounts by the chemical industry, and linked to numerous high-profile crimes. The U.S. Centers for Disease Control and Prevention has identified cyanide as one of the most probable agents to be used in a chemical terrorism event. We investigated whether stable C and N isotopic content of sodium and potassium cyanide could serve as a forensic signature for sample matching, using a collection of 65 cyanide samples. Upon analysis, a few of the cyanide samples displayed nonhomogeneous isotopic content associated with degradation to a carbonate salt and loss of hydrogen cyanide. Most samples had highly reproducible isotope content. Of the 65 cyanide samples, >95% could be properly matched based on C and N isotope ratios, with a false match rate <3%. These results suggest that stable C and N isotope ratios are a useful forensic signature for matching cyanide samples.

10.
J Agric Food Chem ; 58(8): 5109-13, 2010 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-20359248

RESUMO

Carrots are one of the highest dietary sources of beta-carotene and are naturally high in the (all-E)-beta-carotene isomer, which has higher bioavailability, provitamin A activity, and antioxidant capacity compared to Z (cis) isomers. The objectives of the present study were to investigate the effects of storage temperature, time, and cooking (boiling for 15 min) on the levels of carotene isomers in 'Stefano' carrots. Storing carrots at either 4 degrees C to simulate long-term storage or 20 degrees C to simulate marketing practices resulted in increases in (all-E)-beta-carotene of 20.3% after 3 days at 4 degrees C and 34.4% after 14 days at 20 degrees C, respectively. The levels of Z isomers in raw carrots were low with (13Z)-beta-carotene and (9Z)-beta-carotene accounting for less that 1.8% of the total beta-carotene present. Levels of (9Z)-beta-carotene decreased during storage at either temperature, whereas storage at 4 degrees C resulted in a 109% increase in (13Z)-beta-carotene after 56 days. Cooking significantly increased the levels of (13Z)-beta-carotene and (9Z)-beta-carotene and resulted in the production of (15Z)-beta-carotene, which was absent in raw carrots. Storage at 4 degrees C for 15 days or more prior to cooking reduced the susceptibility of (all-E)-beta-carotene to thermal isomerization during cooking, resulting in lower levels of all three Z-beta-carotene isomers being generated, while storage at 20 degrees C for up to 21 days resulted in significantly higher levels of (all-E)-beta-carotene before and after cooking but had no effect on Z-isomer production during cooking. Consequently, we conclude that, for the greatest health benefit, fresh carrots can be stored for up to 21 days at 20 degrees C or at 4 degrees C for up to 56 days without significant reduction in (all-E)-beta-carotene and should be consumed raw or boiled for less than 15 min to limit Z-beta-carotene isomer formation.


Assuntos
Culinária , Daucus carota/química , beta Caroteno/química , Isomerismo
11.
Int J Food Microbiol ; 138(3): 232-7, 2010 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-20156661

RESUMO

Minor shoot injury to glasshouse celery, Cos lettuce and chive plants significantly increased the persistence of applied Escherichia coli (P<0.05). After 1 week, mean counts of about 5 log(10) CFU/g decreased to fewer than 0.5 log(10) CFU/g on the uninjured plants, compared to 4 log(10) CFU/g or more on injured plants. By the end of the 3-week long experiments, counts from the uninjured plants were 0.21 log(10) CFU/g or fewer, but 2.8, 2.3 and 5.1 log(10) CFU/g on injured Cos lettuce, celery and chive plants, respectively. A field experiment using Cos lettuce also showed that shoot injury increased E. coli persistence. Counts from the injured plants on days 1, 3, and 7 were, 4.2, 4.1 and 3.3 log(10) CFU/g, respectively, whereas the uninjured plants returned significantly (P<0.05) lower counts on those days, and were 2.8, 2.0 and 1.2 log(10) CFU/g, respectively. These findings reveal that increased E. coli persistence on injured tissue is common to different vegetables and can occur in the glasshouse and the field. The implications of this study on vegetable production practices are presented.


Assuntos
Escherichia coli , Manipulação de Alimentos , Microbiologia de Alimentos , Viabilidade Microbiana , Doenças das Plantas , Verduras/microbiologia , Contagem de Colônia Microbiana , Brotos de Planta
12.
Anal Chem ; 79(7): 2778-89, 2007 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-17338504

RESUMO

Desorption electrospray ionization mass spectrometry was investigated as a means to qualitatively identify and to quantify analytes directly from developed normal-phase thin-layer chromatography plates. The atmospheric sampling capillary of a commercial ion trap mass spectrometer was extended to permit sampling and ionization of analytes in bands separated on intact TLC plates (up to 10 cmx10 cm). A surface positioning software package and the appropriate hardware enabled computer-controlled surface scanning along the length of development lanes or at fixed Rf value across the plates versus the stationary desorption electrospray emitter. Goldenseal (Hydrastis canadensis) and related alkaloids and commercial dietary supplements were used as standards and samples. Alkaloid standards and samples were spotted and separated on aluminum- or glass-backed plates using established literature methods. The mass spectral signal levels as a function of desorption spray solvent were investigated with acetonitrile proving superior to methanol. The detection levels (approximately 5 ng each or 14-28 pmol) in mass spectral full-scan mode were determined statistically from the calibration curves (2.5-100 pmol) for the standards berberine, palmatine, and hydrastinine spotted as a mixture and separated on the plates. Qualitative screening of the major alkaloids present in six different over-the-counter "goldenseal" dietary supplements was accomplished by obtaining full-scan mass spectra during surface scans along the development lane in the direction of increasing Rf value. In one sample, alkaloids were detected that strongly suggested the presence of at least one additional herb undeclared on the product label. These same data indicated the misidentification of one of the alkaloids in the TLC literature. Quantities of the alkaloids present in two of the samples determined using the mass spectral data were in reasonable agreement with the label values, indicating the quantitative ability of the method. The advantage of mass spectral measurements in identifying and quantifying materials within overlapping bands and in providing positive identification for even minor species in a mixture was also demonstrated.


Assuntos
Alcaloides/análise , Hydrastis/química , Espectrometria de Massas por Ionização por Electrospray/instrumentação , Espectrometria de Massas por Ionização por Electrospray/métodos , Cromatografia em Camada Fina/instrumentação , Cromatografia em Camada Fina/métodos , Estrutura Molecular , Sensibilidade e Especificidade
13.
Rapid Commun Mass Spectrom ; 19(16): 2305-12, 2005.
Artigo em Inglês | MEDLINE | ID: mdl-16021617

RESUMO

A self-aspirating heated nebulizer probe is described and demonstrated for use in the direct analysis of analytes on surfaces and in liquid samples by atmospheric pressure chemical ionization (APCI) mass spectrometry. Functionality and performance of the probe as a self-aspirating APCI source is demonstrated using reserpine and progesterone as test compounds. The utility of the probe to sample analytes directly from surfaces was demonstrated first by scanning development lanes of a reversed-phase thin-layer chromatography plate in which a three-component dye mixture, viz., Fat Red 7B, Solvent Green 3, and Solvent Blue 35, was spotted and the components were separated. Development lanes were scanned by the sampling probe operated under computer control (x, y plane) while full-scan mass spectra were recorded using a quadrupole ion trap mass spectrometer. In addition, the ability to sample the surface of pharmaceutical tablets (viz., Extra Strength Tylenol and Evista tablets) and to detect the active ingredients (acetaminophen and raloxifene, respectively) selectively was demonstrated using tandem mass spectrometry (MS/MS). Finally, the capability to sample analyte solutions from the wells of a 384-well microtiter plate and to perform quantitative analyses using MS/MS detection was illustrated with cotinine standards spiked with cotinine-d3 as an internal standard.


Assuntos
Progesterona/análise , Reserpina/análise , Soluções/química , Espectrometria de Massas por Ionização por Electrospray/instrumentação , Espectrometria de Massas por Ionização por Electrospray/métodos , Pressão Atmosférica , Cromatografia em Camada Fina , Modelos Químicos , Estrutura Molecular , Progesterona/química , Reserpina/química , Comprimidos/química
14.
Anal Chem ; 77(14): 4385-9, 2005 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-16013850

RESUMO

Quantitative determination of caffeine on reversed-phase C8 thin-layer chromatography plates using a surface sampling electrospray ionization system with tandem mass spectrometry detection is reported. The thin-layer chromatography/electrospray tandem mass spectrometry method employed a deuterium-labeled caffeine internal standard and selected reaction monitoring detection. Up to nine parallel caffeine bands on a single plate were sampled in a single surface scanning experiment requiring 35 min at a surface scan rate of 44 mum/s. A reversed-phase HPLC/UV caffeine assay was developed in parallel to assess the mass spectrometry method performance. Limits of detection for the HPLC/UV and thin-layer chromatography/electrospray tandem mass spectrometry methods determined from the calibration curve statistics were 0.20 ng injected (0.50 muL) and 1.0 ng spotted on the plate, respectively. Spike recoveries with standards and real samples ranged between 97 and 106% for both methods. The caffeine content of three diet soft drinks (Diet Coke, Diet Cherry Coke, Diet Pepsi) and three diet sport drinks (Diet Turbo Tea, Speed Stack Grape, Speed Stack Fruit Punch) was measured. The HPLC/UV and mass spectrometry determinations were in general agreement, and these values were consistent with the quoted values for two of the three diet colas. In the case of Diet Cherry Coke and the diet sports drinks, the determined caffeine amounts using both methods were consistently higher (by approximately 8% or more) than the literature values.


Assuntos
Cafeína/química , Cromatografia em Camada Fina/métodos , Espectrometria de Massas por Ionização por Electrospray/métodos
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