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PubMed1979

Reverse phase ion pair high pressure liquid chromatographic determination of ethylenediaminetetraacetic acid in crabmeat and mayonnaise.

A method is described for the determination of ethylenediaminetetraacetic acid (EDTA) in crabmeat and mayonnaise. EDTA is extracted from the food sample with water and converted to its copper chelate, which is then quantitated by reverse phase ion pair high pressure liquid chromatography with ultraviolet detection. Maximum sensitivity is obtained with detection at about 254 nm; higher wavelengths may be used for enhanced specificity. Cleanup procedures for crabmeat and mayonnaise were improved by using a radiotracer method. Analyses of crabmeat and mayonnaise samples spiked at 3 different levels showed greater than 90% recovery of EDTA.

Animals↗

PubMed1998

[Study on the determination of trace mercury in foods by circulating enrichment-cold vapour atomic absorption spectrometry].

The determination of trace mercury using the self-developed circulating enrichment apparatus with cold vapour atomic absorption spectrometry was investigated. Various experimental conditions were discussed and optimized. The effect of interferences was examined. The developed method is sensitive, accurate, simple and available and has already been used in the analysis of various kinds of food samples and national standard reference materials, and the results obtained were satisfactory.

Cold Temperature↗

PubMed1982

Dry ashing, hydride generation atomic absorption spectrometric determination of arsenic and selenium in foods.

A dry ashing, flameless atomic absorption spectrometric method was evaluated to determine arsenic and selenium in foods. Samples were dry-ashed with Mg(NO3)2-MgO and dissolved in HCl. Selenate was reduced to selenite by boiling in 4N HCl. Selenate was reduced to selenite by boiling in 4N HCl, and arsenate to arsenite by treatment with KI. Hydrides of arsenic and selenium were generated by the addition of NaBH4 and were swept by nitrogen and hydrogen into a thermally heated silicate tube furnace. The detection limit was about 5 ppb for each element based on a 10 g sample. Analytical results obtained for several samples of NBS reference materials agreed with the certified values. The procedure was evaluated by another laboratory and results were satisfactory.

Arsenic↗

PubMed2004

Rapid and quantitative detection of the microbial spoilage in chicken meat by diffuse reflectance spectroscopy (600-1100 nm).

AIMS: To evaluate the feasibility of visible and short-wavelength near-infrared (SW-NIR) diffuse reflectance spectroscopy (600-1100 nm) to quantify the microbial loads in chicken meat and to develop a rapid methodology for monitoring the onset of spoilage. METHODS AND RESULTS: Twenty-four prepackaged fresh chicken breast muscle samples were prepared and stored at 21 degrees C for 24 h. Visible and SW-NIR was used to detect and quantify the microbial loads in chicken breast muscle at time intervals of 0, 2, 4, 6, 8, 10, 12 and 24 h. Spectra were collected in the diffuse reflectance mode (600-1100 nm). Total aerobic plate count (APC) of each sample was determined by the spread plate method at 32 degrees C for 48 h. Principal component analysis (PCA) and partial least squares (PLS) based prediction models were developed. PCA analysis showed clear segregation of samples held 8 h or longer compared with 0-h control. An optimum PLS model required eight latent variables for chicken muscle (R = 0.91, SEP = 0.48 log CFU g(-1)). CONCLUSIONS: Visible and SW-NIR combined with PCA is capable of perceiving the change of the microbial loads in chicken muscle once the APC increases slightly above 1 log cycle. Accurate quantification of the bacterial loads in chicken muscle can be calculated from the PLS-based prediction method. SIGNIFICANCE AND THE IMPACT OF THE STUDY: Visible and SW-NIR spectroscopy is a technique with a considerable potential for monitoring food safety and food spoilage. Visible and SW-NIR can acquire a metabolic snapshot and quantify the microbial loads of food samples rapidly, accurately, and noninvasively. This method would allow for more expeditious applications of quality control in food industries.

Food Microbiology↗

PubMed1992

Isoleucine requirements of the chicken: the effect of excess leucine and valine on the response to isoleucine.

1. Three experiments were designed to determine the response of broiler chickens to dietary isoleucine, and to quantify the antagonistic effects of excess leucine and valine on this response. 2. A dilution technique was used to measure the responses in growth rate and food intake to a range of diets differing in their isoleucine concentrations. A summit diet was formulated to contain isoleucine at 1.14 times the requirement and with leucine (1.76 times the requirement) and valine (1.87 times the requirement) at the minimum possible concentrations, given the ingredients available. A dilution mixture, devoid of protein, was formulated to correspond in all respects, other than in amino acid content, to the summit diet. These two basal diets were blended in different proportions to give a range of diets of decreasing isoleucine and protein content. 3. In experiment 1 the response was measured to isoleucine with leucine and valine remaining in the same proportion to isoleucine throughout the range of diets fed. In experiments 2 and 3, however, L-leucine and L-valine were added to the diets either singly or in combination to give 6 isoleucine concentrations and 3 ratios of each of leucine and valine to isoleucine. 4. Weight gain decreased as the isoleucine content of the diet was reduced, whereas food intake of broilers fed on the marginally deficient diets increased to a maximum and then decreased. FCE decreased curvilinearly as the isoleucine concentration in the food decreased, reflecting a concomitant change in the fat content of the broilers. 5. It is possible that the amount of dietary isoleucine assumed to be available to the broilers in these experiments was overestimated by hydrolysing the food samples for 72 h, and the doubt thus created makes an estimate of the efficiency of retention of isoleucine suspect. 6. Excess valine had no effect on the response to isoleucine, whereas an increase in the leucine to isoleucine ratio depressed food intake and hence weight gain, but only at the lowest concentrations of isoleucine. 7. If the food content of isoleucine is sufficient to meet the requirements of the broiler, relatively large excesses of leucine, of valine, or of both will not depress growth.

Animal Feed↗

PubMed1992

Applicability of an immunoblot technique combined with a semiautomated electrophoresis system for detection of staphylococcal enterotoxins in food extracts.

We studied the usefulness of an immunoblot technique for the detection of staphylococcal enterotoxins (SEs) in strains and food extracts. Food samples (milk, yogurt, hot dog sausage, cheese, and mayonnaise) were artificially contaminated with SEA through SEE. Protein A did not interfere with the results; it appeared on electrophoresis gels as bands with molecular weights higher than those of the SEs. Other food proteins were not revealed by the technique. The immunoblot technique proved to be fast, specific, and sensitive for the detection of SEs in foods.

Electrophoresis, Polyacrylamide Gel↗

PubMed1997

In vitro assay of Staphylococcus aureus enterotoxin A activity in food.

Staphylococcus aureus enterotoxin A (SEA) is a leading cause of food poisoning. The current test for functional activity of SEA requires monkeys or kittens. The major drawbacks of animal assays are lack of quantitation, poor reproducibility, low sensitivity, and high cost. In this report we describe and evaluate an alternative assay using T-cell proliferation to measure SEA activity in food. Human and rat lymphocytes proliferate in response to concentrations of SEA as low as 1 pg/ml, well below the pathogenic dose of 100 ng. This proliferation assay is highly sensitive, quantitative, and simple. Nonradioactive assays of T-cell proliferation were also suitable for detecting and measuring SEA, although with a 10-fold lower sensitivity. To evaluate the utility of this assay for food testing, four different food samples were mixed with SEA. In each sample, SEA was detected at a concentration of 1 ng/ml. Heat-inactivated SEA produced no detectable proliferation. These results demonstrate that an in vitro cell proliferation assay is an advantageous alternative to existing animal assays for measuring SEA activity in food.

Animals↗

PubMed2003

Determination of atrazine and carbaryl pesticide residues in vegetable samples using a multianalyte dipstick immunoassay format.

A dipstick assay for the simultaneous determination of atrazine and carbaryl in vegetable samples was developed. The analytical method involved a fast extraction procedure followed by a multi-strip membrane test. The assay took 10 min, with a detection limit (naked eye) of 10 and 200 micro g l(-1) for atrazine and carbaryl, respectively. The cross-reactivities to related compounds tested were negligible except for propazine. Quantification of the pesticides was carried out by measuring the dot colour with a spectrophotometer. IC(50) values (inhibition constant at 50% of the maximum binding) of 2.04 microg l(-1) for atrazine and 92.8 microg l(-1) for carbaryl were achieved by this approach. Vegetable samples were extracted with MeOH. The proposed methodology was used to analyse atrazine and carbaryl and check for compliance with European Union maximum residue levels for vegetables. Recoveries (75-105%) were in agreement with those obtained by GC/MS or HPLC. Standard curves using 25% methanol/75% TBS were used for food sample assays using a multi-analyte dipstick. IC(50) values were 9.2 microg kg(-1) for atrazine and 179.2 microg kg(-1) for cabaryl.

Atrazine↗

PubMed1985

Intestinal carriage of Bacillus cereus: faecal isolation studies in three population groups.

The results of examinations of stools for Bacillus cereus among three unrelated groups of individuals are presented. The groups consisted of (1) healthy school-children aged 6-11 years in a rural region of South Africa examined during each of the four seasons of the year; (2) 15 healthy volunteers comprising staff of a London microbiology laboratory and their families examined on each of 3 consecutive weeks; (3) 75 unrelated young children, 2 months to 5 years of age, in a second rural region of South Africa examined during a pilot study of 1 week's duration on the aetiology of rural gastroenteritis. The stools of the last group were submitted as being related to present or recent diarrhoea in the respective children. In group 1, B. cereus isolation rates ranged from 24.3% at the autumn visit to 43% at the summer visit with a significantly higher rate of isolation in the summer than at other seasons of the year (P less than 0.05). B. cereus was isolated from 40% of group 2 volunteers on week 1, none on week 2 and 20% on week 3. The organism was detected in the 12 positive specimens at levels of approximately 10(2)/g and constituted 2.5-30% of the total aerobic spore-forming bacillus population in the stools. In group 3, B. cereus was recovered from 18.7% of the stool samples and was isolated consecutively with other pathogens (enteropathogenic Escherichia coli and rotavirus) on only five occasions. In groups 1 and 3, less than 5% of the stools had '3+' levels of B. cereus (greater than 10 colonies per direct plate culture). B. cereus was readily isolated from all of 10 food samples, representative of the typical diet of the group 1 individuals, and was present in substantial numbers (10(4) to 5.5 X 10(6)/g) in half of them. The isolation results, supported by serotyping, indicated that carriage of B. cereus in stools is transient and its presence at any one time reflects solely its intake with foods.

Adult↗

PubMed1993

Assessment of cleaning and disinfection in the food industry with the rapid ATP-bioluminescence technique combined with the tissue fluid contamination test and a conventional microbiological method.

A quantitative ATP bioluminescence procedure has been used to determine the cleanliness of food processing factories and the results have been compared with those from conventional microbiological culture methods. ATP measurements were combined with the tissue or tissue fluid contamination (TTFC) assessment method to obtain an impression of the amount of inanimate contamination on the sampled surfaces. It was found that, in the sampled food factories, there was poor relation between the two assessment techniques: ATP bio-luminescence combined with TTFC and contact plating. However, either method in its own right is useful to check cleanliness of food industries. ATP measurements do have in addition the great advantage that it is a fast method and is easy to perform.

Adenosine Triphosphate↗

PubMed2005

Sequencing of an internal transcribed spacer region of 16S-23S rRNA gene and designing of PCR primers for the detection of Salmonella spp. in food.

DNA sequences of an internal transcribed spacer (ITS) region for 40 Salmonella serovars were determined and compared with ITS sequences of Salmonella spp., and non-Salmonella spp. already available on the GenBank database. From such comparison, two Salmonella-specific ITS based PCR primers, ITSF and ITSR, were designed. When Salmonella strains with various serotypes were PCR assayed with primers ITSF/ITSR, all generated PCR products with molecular weight bands equal to 312 bp. On the other hand, 48 non-Salmonella isolates, including strains of Enterobacteriaceae and other food pathogens generated negative results. Detection limits of this PCR method was 1-9 CFU per assay. These PCR primers were used for the detection of Salmonella cells in artificially contaminated foods, including chicken meat and whole milk. The detection limit was 1-9 x 10(3) CFU per assay. With an 8-h enrichment step performed prior to the PCR assay, however, the detection limit became 1-9 CFU per gram of the food sample.

Animals↗

PubMed1978

Comparison of thin-layer chromatographic detection methods for histamine from food extracts.

The specificity and sensitivity of four visualization reagents, ninhydrin, o-phthalaldehyde (OPT), fluorescamine and o-diacetylbenzene (DAB), for the detection of histamine on thin-layer chromatograms developed in several optimal solvent systems were compared. While the ninhydrin reagent is the most sensitive with a detection limit of 0.4 nmoles of histamine, the DAB and fluorescamine reagents offer the most potential as histamine-specific visualization reagents. The OPT reagent was unsatisfactory because the fluorescent sports developed with this reagent were unstable. Of 19 amines tested in addition to histamine, ninhydrine reacted with 17, fluorescamine with 8 and DAB with 15. Since only histidyl-leucine, octopamine, serotonin and tryptophan interfere in the resolution of histamine in any of the solvent systems used, DAB provides some advantages by not reacting with histidyl-leucine. In addition, with the acetone-ammonia (95:5) solvent system, which adequately separates histamine from all other tested amines, no background interference problems were noted when using DAB as the visualization reagent. Background interference problems with the acetone-ammonia system were evident with the other visualization reagents. The sensitivity of the DAB and fluorescamine methods (4 nmoles of histamine) allows both reagents to act as semi-quantitative screening agents for potentially toxic levels of histamine in food extracts. With a variety of food samples, DAB visualization following development in acetone-ammonia (95:5) was the optimal thin-layer chromatographic method.

Chromatography, Thin Layer↗

PubMed2002

Detection of Bacillus cereus in foods by colony hybridization using PCR-generated probe and characterization of isolates for toxins by PCR.

Isolates of Bacillus cereus from traditional Indian foods were detected by colony hybridization using the PCR-generated phospholipase (PL-1) probe. In all, 29 isolates picked up by the probe were confirmed as B. cereus by conventional cultural and biochemical characteristics. All the isolates reacted positively in PCR with phospholipase (PL-1) primers. Among the native isolates, 11 of them showed the discontinuous pattern of haemolysin BL activity in gel diffusion assay. Though 14 isolates reacted positively in PCR with primers (Ha-1) specific to the B gene of haemolysin BL, only four of them showed both the presence of gene and haemolysin BL activity. More than 50% of the isolates indicated their potential enterotoxigenicity by reacting positively with primers specific for the BceT gene encoding for diarrhoeal enterotoxin. PCR with primers for different inverse (IS) repeat elements revealed that isolates carrying transposon IS 231-P 231-1 did not carry IS 240-P 240. Some of the isolates were devoid ofthese IS elements. The study demonstrated the potential of using of a PCR-generated labelled PL-1 probe for the direct detection of B. cereus in food samples and PCR for characterizing the toxigenic isolates.

Bacillus cereus↗

PubMed1985

Reference material for the evaluation of a standard method for the detection of salmonellas in foods and feeding stuffs.

To evaluate a standard salmonella isolation method a reference material consisting of 0.2 g spray-dried milk inoculated with Salmonella typhimurium and contained in gelatin capsules was prepared. The organisms were distributed homogeneously between capsules, and their numbers were stable for 120 d when the capsules were stored in dry conditions at 4 degrees C. Addition of these capsules with or without food samples to pre-enrichment broth gave low and reproducible levels of Salm. typhimurium contamination without altering the pre-enrichment and without influencing the other bacterial flora present. As a result of an interlaboratory trial, the reference material indicated that the food and/or its competitive flora may have a negative influence on the detection of salmonellas.

Animals↗

PubMed1996

Development of a polymerase chain reaction assay for the detection of Listeria monocytogenes in foods.

Species-specific oligonucleotide primers were selected from the coding region of the listeriolysin O gene of Listeria monocytogenes and were used in conjunction with genus-specific primers and an internal control fragment for polymerase chain reaction amplification. The specificity of the primers was confirmed by testing 40 isolates of L. monocytogenes, other Listeria species and other micro-organisms which are ubiquitous in the environment. The reliability of these primers was further tested in parallel with standard cultural methods. In a preliminary study, over 250 different food samples were examined and PCR results were in complete agreement with those obtained from standard cultural procedures.

Bacterial Proteins↗

PubMed1983

Automated capillary gas chromatographic analysis of pesticide residues in food.

A method for multiresidue pesticide analysis in food is described. After a conventional clean-up, gas chromatographic analysis is performed in a gas chromatograph equipped with two fused-silica capillary columns coated with methylsilicone SP 2100 and methylphenylsilicone OV-17. The effluent from each column is split to electron-capture and nitrogen-phosphorus detectors, which are connected to a dual channel integrator. Therefore, from each gas chromatographic run parallel records of signals from the two detectors are obtained. Calibration of the system is carried out for the SP 2100 column with three test mixtures covering all pesticides. Additionally, four internal standards are included, two responding to the electron-capture detector and the other two to the nitrogen-phosphorus detector. Automated analysis is performed with test mixtures and food samples on the SP 2100 column overnight as a screening procedure. After selection of positive samples a confirmatory test and quantitation are carried out manually applying appropriate test mixtures according to the results of the screening runs.

Chromatography, Gas↗

PubMed1989

Specific gene probe for detection of biotyped and serotyped Listeria strains.

A total of 284 strains of Listeria, including all known serovars and biovars together with Listeria grayi and Listeria murrayi, were biotyped and serotyped. Biotyping and serotyping could be done in 2 days. A gene probe encoding a delayed hypersensitivity factor (DTH) was used in the detection of pathogenic biotypes and serotypes of the tested strains. The gene was found in all 117 tested Listeria monocytogenes strains of serogroups 1/2a, 1/2b, 1/2c, 3a, 3b, 3c, 4c, 4d, 4e, 4ab, and 7. It was also present in Listeria ivanovii. Of 78 L. monocytogenes strains of serogroup 4b, 77 strains contained the gene, whereas it was absent in all 10 tested L. monocytogenes strains of serogroup 4a. Furthermore, the gene was absent in Listeria seeligeri, L. grayi, L. murrayi, and L. innocua of serogroups 3c, 4b, and 6a and in L. welshimeri of serogroups 1/2b, 3b, 6a, and 6b. Since L. monocytogenes and L. ivanovii are the only two biotypes of the genus Listeria considered pathogens, the data obtained indicate that the DNA probe tested may be a useful tool in the detection of virulent Listeria isolates in clinical, environmental, and food samples.

Bacterial Typing Techniques↗

PubMed2005

[Determination of fumonisin biosynthesis gene and toxicity of Fusarium moniliforme strains isolated in China].

OBJECTIVE: To study the relationship between fumonisin biosynthesis gene and toxicity of Fusarium moniliforme isolated in China. METHODS: The toxigenic gene of 29 Fusarium moniliforme isolated from different provinces and varied food samples were determined. Eighteen fum5-positive strains were selected for biosyhesizing fumonisin and determined by high performance liquid chromatography (HPLC). RESULTS: Twenty-six isolates were identified as fum5 gene positive strains. And all of these strains produced FB(1), FB(2) and FB(3). The amount of FB(1), FB(2) and FB(3) was ranging from 0.41-140.20 mg/kg, 0.06-14.30 mg/kg to 0.30-58.00 mg/kg, except one strain produced a lower level of FB(1) only. It wight be the first report showing a high level fumonisin-producing strain isolated from the sesame sample and identified in the world. The amount of FB(1), FB(2) and FB(3) produced by the isolate was 128.84 mg/kg, 11.80 mg/kg and 14.88 mg/kg. CONCLUSIONS: It should have a close relationship between fumonisins biosynthesis gene and toxicity of Fusarium moniliforme isolated in China. The study demonstrated that strain of Fusarium moniliforme might contaminate the sesame sample and produce a high level of fumonisins.

China↗