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PubMed2005

Chiral comprehensive two-dimensional gas chromatography with electron-capture detection applied to the analysis of chiral polychlorinated biphenyls in food samples.

The feasibility of comprehensive two-dimensional gas chromatography with electron-capture detection (GC x GC-ECD) for the enantioseparation of chiral PCBs from other possible interfering compounds has been evaluated. Three commercially available enantioselective beta-cyclodextrin-based capillary columns (Chirasil-Dex, BGB-172 and BGB-176SE) have been tested as first-dimension columns. Three non-enantioselective stationary phases (HT-8, BPX-50 and Supelcowax-10) were combined with the enantioselective columns to allow the unambiguous determination of the enantiomers of the target chiral PCBs. Each enantioselective first-dimension column tested was able to separate into enantiomers different PCB congeners, but in all cases, the use of Supelcowax-10 as second-dimension column provided the most satisfactory results. The Chirasil-Dex x Supelcowax-10 column combination allowed the determination of the enantiomeric fraction (EF) of PCBs 84, 91, 95, 132, 136, 149, 174 and 176 in the working standard solution, while that of congener 135 was hindered. The BGB-172 x Supelcowax-10 column set allowed a proper EF determination of congeners 45, 84, 131, 132, 135, 171, 174 and 183, while that of PCB 91 was interfered with co-elutants. The column combination BGB-176SE x Supelcowax-10 allowed the determination of all congeners that this enantioselective stationary phase was able to separate into enantiomers, i.e. PCBs 45, 91, 95, 136, 149 and 176. These column combinations have also been evaluated for the simultaneous determination of the 12 congeners with a toxic equivalency factor assigned by the WHO (PCBs 77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169, 189) and the seven indicator congeners (PCBs 28, 52, 101, 118, 138, 153 and 180), and evaluated for the analysis of food samples.

Chromatography, Gas↗

PubMed2005

Determination of preservatives in cosmetics and food samples by micellar liquid chromatography.

An analytical procedure has been developed for the analysis of benzoic acid, p-hydroxybenzoic acid, methyl-, ethyl-, propyl-, isopropyl-, and butyl esters of p-hydroxybenzoic acid by micellar liquid chromatography. After dilution in n-propanol the sample was directly injected onto a Lichrosorb ODS, 5 microm (250 x 4.6 mm ID) column and eluted with aqueous 2% Brij-35 adjusted to pH 3.0 with phosphoric acid:propanol (80:20 v/v) at a flow rate of 1 mL min(-1) and UV detection at 254 nm. A linear calibration curve was obtained simultaneously for each component in the range of 50-500 microg mL(-1) for benzoic acid and 5-150 microg mL(-1) for the other components; detection limits were within 25-250 ng mL(-1) corresponding to 125-1250 pg per injection (5 microL). The reproducibility in terms of average peak area and average retention time was obtained with coefficients of variation (CV) of 1.2% and 0.5%. The method was applied to analysis of these compounds in cosmetics (shampoos, hand lotions, creams, and bath foam) and food samples.

Animals↗

PubMed2006

Development of cholesterol biosensor based on immobilized cholesterol esterase and cholesterol oxidase on oxygen electrode for the determination of total cholesterol in food samples.

The development of a cholesterol biosensor by co-immobilization of cholesterol esterase (ChEt) and cholesterol oxidase (ChOX) on oxygen electrode is described. The electrode consists of gold cathode and Ag/AgCl anode. The enzymes were immobilized by cross-linking with glutaraldehyde and Bovine Serum Albumin (BSA). The immobilized enzymatic membrane was attached to the tip of the electrode by a push cap system. The optimum pH and temperature of the sensor was determined, these are 6 and 25 degrees C respectively. The developed sensor was calibrated from 1-75 mg/dl of cholesterol palmiate and found linear in the range of 2-50 mg/dL. The calibration curve was drawn with V(i) (ppm/min)(initial velocity) vs different concentrations of cholesterol palmiate (mg/dL). The application of the sensor to determine the total cholesterol in different real food samples such as egg, meat was investigated. The immobilized enzymatic layer can be reused over 30 times and the stability of the enzymatic layer was studied up to 9 weeks.

Biosensing Techniques↗

PubMed2003

Assays for hydrophilic and lipophilic antioxidant capacity (oxygen radical absorbance capacity (ORAC(FL))) of plasma and other biological and food samples.

Methods are described for the extraction and analysis of hydrophilic and lipophilic antioxidants, using modifications of the oxygen radical absorbing capacity (ORAC(FL)) procedure. These methods provide, for the first time, the ability to obtain a measure of "total antioxidant capacity" in the protein free plasma, using the same peroxyl radical generator for both lipophilic and hydrophilic antioxidants. Separation of the lipophilic and hydrophilic antioxidant fractions from plasma was accomplished by extracting with hexane after adding water and ethanol to the plasma (hexane/plasma/ethanol/water, 4:1:2:1, v/v). Lipophilic and hydrophilic antioxidants were efficiently partitioned between hexane and aqueous solvents. Conditions for controlling temperature effects and decreasing assay variability using fluorescein as the fluorescent probe were validated in different laboratories. Incubation (37 degrees C for at least 30 min) of the buffer to which AAPH was dissolved was critical in decreasing assay variability. Lipophilic antioxidants represented 33.1 +/- 1.5 and 38.2 +/- 1.9% of the total antioxidant capacity of the protein free plasma in two independent studies of 6 and 10 subjects, respectively. Methods are described for application of the assay techniques to other types of biological and food samples.

Adult↗

PubMed2002

Determination of trace molybdenum in vegetable and food samples by spectrophotometry with p-carboxyphenylfluorone.

A new highly sensitive and selective chromogenic reagent, p-carboxyphenylfluorone (p-CPF), was studied for spectrophotometric determination of trace molybdenum. In 0.36 mol L(-1)phosphoric acid medium, p-CPF reacts with molybdenum(VI) to form a 1:3 red complex, which has a sensitive absorption peak at 531 nm. Under optimal conditions, the reaction of molybdenum(VI) with p-CPF completed rapidly and absorbance remains almost constant for at least 24 h. Molybdenum(VI) obeyed Beer's law in the range 0-2.0 microg mL(-1); the apparent molar absorption coefficient, Sandell's sensitivity and the limit of detection were found to be 1.03 x 10(5) L mol(-1) cm(-1), 1.028 ng cm(-2)and 0.73 ng mL(-1) respectively; the effect of various foreign ions were examined in detail. It was found that most coexisting ions can be tolerated in considerable amounts, especially 800 mg of Mn(II), 200 mg of Mg(II), Fe(II), Co(III), Ni(II) and Cd(II), 50 mg of Ca(II) and Al(III), 25 mg of Cu(II) and Fe(III), 10 mg of Hg (II), La(III), Bi(III), Pb(II) and Zn(II) don't interfere with the determination of molybdenum(VI). The proposed method is very simple, sensitive and selective, it has been applied to determine molybdenum in vegetable and food samples with a very high precision and accuracy. Moreover, the synthesis of the reagent and the conditions of the colour reaction were also studied in detail.

Artifacts↗

PubMed2005

6-Oxy-(N-succinimidyl acetate)-9-(2'-methoxycarbonyl)fluorescein as a new fluorescent labeling reagent for aliphatic amines in environmental and food samples using high-performance liquid chromatography.

6-Oxy-(N-succinimidyl acetate)-9-(2'-methoxycarbonyl)fluorescein (SAMF), a new fluorescein-based amine-reactive fluorescent probe was well designed, synthesized and used as a pre-column derivatizing reagent for the determination of aliphatic amines in HPLC. It exhibited relatively pH-independent fluorescence (pH 4-9) and excellent photostability. The derivatization was performed at room temperature in 6min. On a C18 column, the derivatives of SAMF with eight aliphatic amines were baseline separated in 28 min with a mobile phase of methanol-water (57:43, v/v) containing 10 mmol l(-1) pH 5.0, H3Cit3-NaOH buffer. With fluorescent detection at lambda(ex)/lambda(em) = 484/516 nm, the detection limit could reach 2-320 fmol (signal-to-noise = 3), which was equivalent to or better than the detection limits obtained from other analytical methods of aliphatic amines. The proposed method has been applied to the determination of the aliphatic amines in environmental and food samples such as lake water, red wine, white wine, and cheese with satisfying recoveries varying from 95 to 106%.

Amines↗

PubMed2005

Enantiomeric separation of chiral polychlorinated biphenyls on beta-cyclodextrin capillary columns by means of heart-cut multidimensional gas chromatography and comprehensive two-dimensional gas chromatography. Application to food samples.

Three commercially available chiral capillary columns, Chirasil-Dex, BGB-176SE, and BGB-172, have been evaluated for the separation into enantiomers of the 19 chiral polychlorinated biphenyls (PCB) congeners stable at room temperature. The enantiomers of 15 chiral PCBs were, at least to some extent, separated using these beta-cyclodextrin based columns. Multidimensional techniques, such as heart-cut multi-dimensional gas chromatography (heart-cut MDGC) and comprehensive two-dimensional gas chromatography (GC x GC), were investigated for their ability to solve coelution problems with other PCBs present in commercial mixtures and real-life samples. Heart-cut MDGC improved the separation as compared to one-dimensional GC, and enantiomeric fractions of the investigated chiral PCBs could be determined free from interferences. However, limitations on the number of target compounds that can be transferred to the second column in a single run and, therefore, the time consumption, have led to the evaluation of GC x GC as an alternative for this type of analysis. With GC x GC, two column set-ups were tested, both having a chiral column as first-dimension column, and two different polar stationary phase columns in the second dimension. On using both column combinations, congeners 84, 91, 95, 132, 135, 136, 149, 174, and 176 could be determined free from coelutions with other PCBs. Results on the application of heart-cut MDGC to food samples such as milk and cheese are given, as well as the first results on the application of GC x GC to this type of samples.

Animals↗

PubMed1989

Volatile nitrosamine levels and genotoxicity of food samples from high-risk areas for nasopharyngeal carcinoma before and after nitrosation.

Traditional life-style, especially food habits, infection by Epstein-Barr virus (EBV) and genetic factors, have been associated with an increased risk of nasopharyngeal carcinoma (NPC). N-Nitroso compounds and other carcinogens either present in food or formed endogenously, as well as food constituents that activate EBV, have been suspected as etiological factors in NPC pathogenesis. For their characterization preserved food items, frequently consumed in NPC endemic areas in Tunisia, South China and Greenland, were sampled and screened for the presence of mutagens and volatile nitrosamines before and after nitrosation. Aqueous extracts as well as 2 organic extracts of the samples were assayed for genotoxicity in 2 Salmonella typhimurium strains and the SOS chromotest. The same extracts had previously been analyzed for volatile nitrosamines and for EBV-activating substances in Raji cells. In our study, 13 out of 16 food samples showed a weak, directly-acting genotoxicity in the SOS chromotest in at least one of the extracts, but only one sample from Greenland was found to be weakly mutagenic in Salmonella TA 98. Chemical nitrosation for 9 out of 15 samples of aqueous food extracts increased the genotoxic effect in the SOS chromotest. Levels of volatile nitrosamines were also elevated for 12 out of 15 samples; highest levels of N-nitrosodimethylamine were found in hard salted and dried fish from China (1,200 micrograms/kg) and highest N-nitrosopyrrolidine levels in a Tunisian spice (3,840 micrograms/kg). In non-nitrosated aqueous food extracts, the level of volatile nitrosamines and genotoxic activities were not correlated with the EBV-inducing activity of the same samples. After chemical nitrosation, EBV-inducing activity was decreased or showed no change and was not correlated with increases in either the genotoxicity or the nitrosamine levels. Our results suggest that EBV-activating compounds belong to a different class of substances. However, there was an association between the changes in genotoxicity and nitrosamine levels due to nitrosation.

Carcinoma↗

PubMed1999

Determination of D-amino acids labeled with fluorescent chiral reagents, R(-)- and S(+)-4-(3-isothiocyanatopyrrolidin-1-yl)-7-(N, N-dimethylaminosulfonyl)-2,1,3-benzoxadiazoles, in biological and food samples by liquid chromatography.

D-Amino acids in food and biological samples labeled with R(-)- and S(+)-4-(3-isothiocyanatopyrrolidin-1-yl)-7-(N, N-dimethylaminosulfonyl)-2,1,3-benzoxadiazoles (DBD-PyNCS) were separated by reversed-phase chromatography and detected fluorometrically at 550 nm (excitation at 460 nm). DL-Amino acids were efficiently labeled at 55 degrees C for 20 min in basic medium. The resulting thiocarbamoyl-amino acids were resolved by an isocratic elution using water:30% methanol in acetonitrile (72:28) containing 0.1% trifluoracetic acid as mobile phase for hydrophilic amino acids and gradient elutions using sodium acetate buffer (pH 5. 2)/acetonitrile as gradient solvent mixture for hydrophobic amino acids, respectively. The detection limits (S/N = 3) of DL-amino acids tested were in the range of 0.16-0.75 pmol. The proposed method was applied to determine the D-amino acid(s) in milk, cream, fermented dairy products (yogurt and yakult), tomato products (juice, puree, and catchup), fermented beverages (beer and red wine), and human urine. The existence of D-amino acid(s) was demonstrated in all the samples tested. Furthermore, the identification of the D-amino acid(s) was performed using both isomers of DBD-PyNCS and by on-line HPLC-electrospray ionization-MS.

Amino Acids↗

PubMed2003

Polychlorinated biphenyls (PCBs) detection in food samples using an electrochemical immunosensor.

In this work, a disposable electrochemical immunosensor, based on a competitive assay scheme, was applied to detect polychlorinated biphenyls (PCBs) in food. For this purpose, antibodies against PCBs were directly immobilized onto the carbon surface of a disposable screen-printed electrode. A competition between the PCBs present in the sample and a fixed concentration of an enzyme-labeled PCB was realized and evaluated by electrochemical detection. Alkaline phosphatase was used as the enzyme label, coupled with differential pulse voltammetry (DPV) as the electrochemical technique. The immunosensor was tested on aroclor mixture detection (1242 and 1248) and then on some typologies of food samples to evaluate the possible application for real sample analysis. Samples analyzed were from different matrixes, such as sheep milk, bovine adipose tissue, and bovine muscle. Results obtained were compared with the accredited results according to ISO 17025 methods for PCB detection (HRGC-LRMS) as a confirmatory analysis. Preliminary results show the possibility to use this device as a screening method in food sample analysis. The negligible matrix effect observed may lead to a simplified extraction procedure, and considerable time and consumable savings are the immediate benefits given by the proposed method.

Electrochemistry↗

PubMed2006

[Molecular typing of Listeria monocytogenes isolated from clinical and food samples].

INTRODUCTION: Listeria monocytogenes is an emergent foodborne pathogen acquired by the ingestion of contaminated food. This bacterium causes a disease called listeriosis, whose mortality rate world wide is around 20% to 30%, reaching up to 80% in cases of neonatal infections. The random amplified polymorphic DNA technique allows different isolates to be distinguished and characterized at the molecular level, which can provide useful information about the diversity of this pathogen in Colombia. OBJECTIVE: To molecularly characterize different L. monocytogenes isolates from food and clinical samples using this technique to determine possible relationships among these two origins. MATERIALS AND METHODS: Thirty eight L. monocytogenes isolates were analyzed; 22 from human clinical samples and 16 from food processing plants and food using two 10bp primers (HLW74, Arbitrary). The data were analyzed using Quantity One and SYN-TAX software. RESULTS: A high percentage of polymorphism was detected with both primers (HLWL-74, 81.81%; Arbitrary, 85.71%). Two major lineages were found, which were divided into four major clusters (A, B C and D) and great genetic diversity was observed. Most of the clinical isolates were grouped within the same cluster, and were more distantly related to the food isolates. CONCLUSION: The results of this study demonstrate a high degree of genetic diversity of DNA polymorphisms among the L. monocytogenes isolates circulating in Colombia, which could reflect phenotypic and pathogenic differences in these isolates.

Bacterial Typing Techniques↗

PubMed2002

Cold vapour atomic fluorescence spectrometry and gas chromatography-pyrolysis-atomic fluorescence spectrometry for routine determination of total and organometallic mercury in food samples.

Two procedures have been investigated for the quantification of the different forms of mercury in food. A two-stage procedure has been developed to determine firstly total inorganic and organometallic species, and then the full separation of all organomercury species. The procedure involves solubilisation of the samples using alkaline extractions or enzymolysis, followed by the extraction of organic mercury in an organic solvent, preferably a mixture of dichloromethane and hexane (3:2). For the total organic mercury determination, the organic extract is analysed for "total" mercury after nitric acid/peroxide digestion, evaporation of the solvent and detection by cold vapour-atomic fluorescence spectrometry. Full organomercury speciation requires a clean-up step before analysis of the final extract in dichloromethane by gas chromatography coupled to a pyrolyser and an atomic fluorescence detector (GC-pyro-AFS). A detection limit of 6 ng l-1, and reproducibility of 2% was achieved for the CV-AFS method; GC-pyro-AFS yielded 200 ng l-1 and 5% for detection limit and coefficient of variation, respectively. Both procedures were validated with the use of various certified reference materials over a wide range of mercury concentrations, and by spiking experiments. The validated methods were tested successfully on a wide range of commercially available food samples.

Chromatography, Gas↗

PubMedDate not supplied

Analytical methods for determining ascorbic acid in biological samples, food products, and pharmaceuticals.

Over the last decade, numerous publications have appeared describing analyses for ascorbic acid in food products, pharmaceuticals, and biological samples. This review focuses on the chemistry associated with many of these procedures. The papers discussed have historical importance, are important to understanding the method, or have significantly advanced ascorbic acid analysis. The review has 4 major sections: spectroscopic, electrochemical, enzymatic, and chromatographic methods of analysis.

Animals↗

PubMed2004

Detection of campylobacter and Shigella species in food samples using an array biosensor.

Campylobacter and Shigella bacteria are common causes of food- and water-borne illness worldwide. There is a current need in food, medical, environmental, and military markets for a rapid and user-friendly method of detecting such pathogens. The array biosensor developed at the NRL encompasses these qualities. In this study, 25-min, sandwich immunoassays were developed for the detection of Campylobacter and Shigella species in both buffer and a variety of food and beverage samples. The limit of detection for Shigella dysenteriae in buffer and chicken carcass wash was 4.9 x 10(4) cfu mL(-)(1), whereas Campylobacter jejuni could be measured at concentrations as low as 9.7 x 10(2) cfu mL(-)(1). The limits of detection and dynamic range were found to vary depending on the sample matrix, but could be improved by running the sample over the waveguide surface for longer periods of time. Samples were run with no preconcentration or enrichment steps and little-to-no sample pretreatment prior to analysis.

Journal Article↗

PubMed1995

Ochratoxin A levels in human milk and related food samples: an exposure assessment.

Ochratoxin A (OA) is a mycotoxin detected in a variety of food and feeds mostly from countries with temperate or continental climate, because the fungi that produce it, mainly Aspergillus ochraceus, Penicillium verrucosum, and Penicillium viridicatum, can grow under a great variety of climate conditions. The aim of this article was, firstly, to confirm the occurrence of OA in human milk in Italy. Then, a preliminary calculation of OA intake via human milk was made, from ingested food. For this investigation, food and milk samples were collected, continuously for a week, from 4 lactating mothers. The obtained results revealed a significant exposure of sucklings and mothers to OA levels higher than the tolerable daily intake as estimated from animal models. On the basis of these data, a major effort in planning surveillance and research programs to control OA contamination in food, feed, and biological fluids should be pursued.

Beer↗

PubMed1992

Radioactive contamination of food sampled in the areas of the USSR affected by the Chernobyl disaster.

In October 1990 a Netherlands humanitarian fact finding mission on aid to people affected by the Chernobyl disaster visited contaminated regions in Russia, Byelorussia and the Ukraine. The mission consisted of medical, socio-psychological and agricultural experts. The results of radioactivity measurements on food products sampled in the contaminated areas are reported here and the radiation burden for the Soviet citizens due to these products is discussed. The radiocaesium contamination measured in 19 food products ranged between 0 and 170 Bq kg-1 and 40K from 25 to 200 Bq kg-1 in the fresh product. Strontium-90, measured in a few samples, was found to be between 1.8 and 30 Bq kg-1. Mushrooms and reindeer moss were very highly contaminated: from 103,000 to 284,000 Bq kg-1 of radiocaesium in the fresh product. Strontium-90 in these samples was 7.8-1550 Bq kg-1. The contamination of all food products was far below the stated limits, except for mushrooms. Extrapolation of the results to the total food consumption gave the radioactive burden due to this food as an estimated 0.2 mSv per year. All of the food products investigated, except mushrooms, can be regarded as safe with respect to radioactive contamination. In addition to sampling agricultural produce, field exposure measurements were also carried out. The measured values, expressed in equivalent doses, ranged from 1.8 to 14 mSv per year at a height of 1 m, with a median value of about 4 mSv per year.

Accidents↗

PubMed2000

Evaluation of dry sheet medium culture plate (Compactdry TC) method for determining numbers of bacteria in food samples.

The Compactdry, a ready-to-use and self-diffusible dry medium sheet culture system, has been developed by the Nissui Pharmaceutical Co. Ltd. for enumerating bacteria in food. The Compactdry consists of special spread sheet with culture medium that is the same as standard method nutrients, a cold water-soluble gelling agent, and a unique plastic dish. The procedure for bacterial examination in a sample solution (1 ml) is to just inoculate a test solution into the center of the self-diffusible medium and incubate at 35 degrees C for 48 h. The Compactdry TC (CTC) for the enumeration of total aerobic bacteria from 97 food samples was compared with the standard plate count (SPC) method and 3M Petrifilm aerobic count plates (PAC). The correlation coefficients between the CTC and SPC method, the CTC and PAC, and the PAC and SPC method were 0.97, 0.99, and 0.97, respectively. The Compactdry system is useful for the enumeration of total aerobic bacteria in food and may be a possible suitable alternative to the conventional pour-plate or the Petrifilm plate methods.

Colony Count, Microbial↗

PubMed2006

A novel generic dipstick-based technology for rapid and precise detection of tetracycline, streptogramin and macrolide antibiotics in food samples.

Excessive use of antibiotics in veterinary medicine and as growth promoters in stock farming has been associated with the dramatically increasing prevalence of multidrug-resistant human pathogenic bacteria. European community legislators have therefore restricted the veterinary use of antibiotics and banned them as growth-promoting food additives in stock breeding (1831/2003/EC). The monitoring of such legislation requires technology for precise and straightforward on-site quantification of antibiotics in farm samples and food products without the need for extensive laboratory equipment and trained personnel. Capitalizing on bacterial transcriptional regulators (TetR, PIP, E), which are dose-dependently released from their cognate operators (tetO, PIR, ETR) upon binding of specific classes of antibiotics (tetracycline, streptogramins, macrolides) we have designed an easy-to-handle dipstick-based assay for detection of antibiotic levels in serum, meat and milk whose detection limits are up to 40-fold below licensed threshold values. The generic dipstick consists of either nitrocellulose, nylon or polyvinylidenfluorid (PVDF) membrane strips coated with streptavidin and immobilized biotinylated operator DNA, which acts as capture DNA to bind hexa-histidine (His(6))-tagged bacterial biosensors. Antibiotics present in specific samples triggered the dose-dependent release of the capture DNA-biosensor interaction, which, after dipping into two different solutions, results in a correlated conversion of a chromogenic substrate by a standard His(6)-targeted enzyme complex. This can be quantified by comparison of the dipstick to a standardized color scale or by assessing the terminal solution at 450nm. As demonstrated using serum, meat and milk samples spiked with 14 different antibiotics, the dipstick technology provided sensitive detection in a rapid assay format, and could be employed to monitor non-authorized use of antibiotics and to discover novel antibiotics.

Animals↗