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PubMed2006

Detection of Listeria monocytogenes in food using a combined enrichment/real-time PCR method targeting the prfA gene.

A combined enrichment/real-time PCR method for the detection of Listeria monocytogenes is presented. The method is based on a conventional PCR assay targeting the prfA gene, which has been validated and suggested as an international standard PCR method for identifying L. monocytogenes in food. This real-time PCR assay includes an internal amplification control. Inclusivity and exclusivity were 100% each when testing 100 L. monocytogenes isolates, 30 Listeria spp. isolates other than L. monocytogenes, and 29 non-Listeria isolates. The theoretical detection limit was one copy of the target gene per PCR reaction and the practical detection limit was about 5 copies per PCR. Using the combined enrichment/real-time PCR method, 7.5 CFU/25 ml of artificially contaminated raw milk, and 9, 1, and 1 CFU/15 g of artificially contaminated salmon, pâté, and green-veined cheese, respectively, were detected. When analyzing 76 naturally contaminated food samples of various types and comparing the results with the ISO 11290-1 standard method, the relative accuracy was 96%, the relative specificity 100%, and the relative sensitivity, 76.9%.

Animals↗

PubMed1983

Preliminary evaluation of high-performance liquid chromatography with photoconductivity detection for the determination of selected pesticides as potential food contaminants.

The applicability of the Tracor Model 965 photoconductivity detector to the determination of a variety of pesticide chemicals, particularly polar and/or thermally labile compounds which are troublesome in gas chromatographic analysis, has been investigated. The effects of various operating parameters (e.g., mobile phase composition, flow-rate and irradiation wavelength) on signal-to-noise output for selected compounds have been evaluated. A comparison of photoconductivity responses with those obtained from a UV detector connected in tandem was made for selected reference standards and food sample extracts. The photoconductivity detector was found to be suitable for the determination of pesticide residues at sub-parts-per-million levels. The linearity and reproducibility of response are adequate for practical quantitative applications.

Chromatography, High Pressure Liquid↗

PubMed1989

Profiling of Alternaria mycotoxins in foodstuffs by high-performance liquid chromatography with diode-array ultraviolet detection.

The potential of high-performance liquid chromatography (HPLC) with diode-array detection for the profiling of mycotoxins in food samples has been demonstrated. A gradient elution reversed-phase chromatographic method coupled with a suitable extraction procedure was devised for the separation and detection of major Alternaria mycotoxins in foodstuffs. Altenuene, alternariol, alternariol methyl ether (dibenzo-alpha-pyrone derivatives), altertoxin-I and altertoxin-II (perylene derivatives) were profiled in extracts of artificially infected maize, rice and tomato samples and naturally contaminated sunflower seeds. First evidence of the occurrence of a new dibenzo-alpha-pyrone derivative in Alternaria cultures is also reported.

Alternaria↗

PubMed2003

Acid tolerance and gad mRNA levels of Escherichia coli O157:H7 grown in foods.

We examined the acid tolerance and gad mRNA levels of Escherichia coli O157:H7 (three strains) and nonpathogenic E. coli (strains K12, W1485, and B) grown in foods. The E. coli cells (approximately 30,000 cells) were inoculated on the surface of 10 g of solid food samples (asparagus, broccoli, carrot, celery, cucumber, eggplant, ginger, green pepper, onion, potato, radish, tomato and beef) and in 10 ml of cow's milk, cultured statically at 10-25 degrees C for 1-14 days, and subjected to an acid challenge at 37 degrees C for 1 h in LB medium (pH 3.0). When grown at 20 and 25 degrees C in all foods, except for tomato and ginger, the strains showed a stationary-phase specific acid tolerance. The acid tolerance of the O157 strains changed depending on the types of foods (3-10% survival), but was clearly lower than that of the cells grown in EC medium (more than 90% survival). Tomato and ginger induced relatively high acid tolerances (10-30% survival) in the O157 strains irrespective of the growth phase, probably because of their acidity. No remarkable difference was observed in the acid tolerance between the O157 and nonpathogenic strains grown in all foods. When grown at 10 and 15 degrees C in the foods and EC medium, none of the strains showed the stationary-phase specific acid tolerance. In beef, broccoli, celery, potato and radish, the acid tolerance showed a tendency to decrease with the prolonged cultivation time. In other foods, the acid tolerance was almost constant (about 0.1% survival) irrespective of the growth stage. The mRNA level of glutamate decarboxylase genes (gadA and gadB) correlated to the acid tolerance level when the E. coli cells were grown at 25 degrees C, but was very low even in the stationary phase when the E. coli cells were grown at 15 degrees C or below.

Adaptation, Physiological↗

PubMed1996

Effect of urea treatment on recovery of staphylococcal enterotoxin A from heat-processed foods.

The effects of urea treatment on the potential reactivation of heat-damaged antigenic components of staphylococcal enterotoxin A (SEA) were examined with cooked foods, including mushrooms, ham, bologna, salami, and turkey. The thermal stability of purified SEA spiked into foods and native SEA produced by Staphylococcus aureus in foods was also examined. Food samples containing either spiked or native SEA were thermally processed by autoclaving or retorting. This was followed sequentially by toxin extraction, urea treatment, dialysis, reconstitution, and SE assays with the reversed passive latex agglutination and/or enzyme immunoassay kit. The results indicate that (i) urea treatment did not result in any reactivation of heat-inactivated antigenic components of SEA in any of the foods tested, (ii) the serological components of purified SEA were destroyed (> or = 96%) by autoclaving at 121.1 degrees C for 5 to 15 min or by retorting at an F0 of 4 to 18, and (iii) the immunological property of the native SEA was approximately threefold-more heat resistant than that of the purified SEA. The study suggested that the current urea method is not suitable for the detection of heat-denatured SEA in the thermally processed foods.

Enterotoxins↗

PubMed1978

Nutrient levels of some foods of Eskimos from Artic Bay, N. W.T., Canada.

Native food samples of caribou, seal, and arctic char were collected from resident Eskimos in Arctic Bay, N.W. T., and analyzed for nutrients. Caribou and seal meats were similar in protein and fat content in comparison with beef. Arctic char was above the average in protein and fat content for fish. Ascorbic acid was present in significant amounts only in baby seal liver. Thiamin, riboflavin, vitamin B12, folacin, and pantothenic acid content ranged from average to high for seal and carbiou meat, respectively, in comparison to published values for pork and beef. The vitamin B6 content of caribou meat was comparable to average values reported for pork and beef but was lower in seal meat. Baby seal liver contained similar levels of thiamin, riboflavin, vitamin B12, folacin, and pantothenic acid and less vitamin B6 than those reported for pork, beef, calf, and lamb liver. Arctic char was not appreciably different in these vitamins from other fish. The iron content of the Eskimo foods was higher than the meat group of the mixed Canadian diet. The macro mineral nutrients in these foods were comparable to those in beef and fish. The amino acid composition of caribou and seal meat was similar to beef, except that seal meat had a lower content of sulfur-containing amino acids and a much higher content of histidine. The sample of seal and arctic char were relatively high in concentrations of long-chain unsaturated fatty acids.

Amino Acids↗

PubMed2006

Real-time PCR assay for rapid detection and quantification of Campylobacter jejuni on chicken rinses from poultry processing plant.

Campylobacter jejuni (C. jejuni) is the leading cause of food-borne gastroenteritis in the United States. Detection of Campylobacter in food samples by conventional culture is cumbersome; therefore, there is a need to develop rapid and cost-effective detection and quantification methods. Eighty-four whole chicken rinses were collected at different stages of processing at three poultry processing plants. After chicken wash collection and DNA extraction, the samples were directly subjected to real-time PCR (rtPCR) without enrichment and also culture. The assay specificity was determined with a range of Campylobacter species, related, and unrelated organisms. Of the 84 samples collected 65 (77%) of the samples were positive by the rtPCR assay and 27 (32%) of the samples tested positive by direct plating to selective agar media. The results were positively concordant for 27 (32%) of the samples. The whole rtPCR assay can be completed within 90min with a detection limit of 1CFU, compared to 5-7 days for enrichment and sub culturing in selective agar. This assay is the first report of rtPCR method capable of detecting and quantifying C. jejuni from chicken rinses without an enrichment step and could be an important, rapid and quantification model for other food-borne pathogens.

Animals↗

PubMed2001

Surface plasmon resonance analysis of staphylococcal enterotoxin B in food.

Surface plasmon resonance (SPR) biosensors are electro-optical instruments used for analyzing real-time protein-protein interactions. This work evaluates an SPR biosensor (Biacore 3000) in the detection of staphylococcal enterotoxin B (SEB) in foods. A sandwich SPR immunosensor involving two antibodies was used. The capturing antibody, bound covalently to the surface of the biosensor chip, performs the initial binding of the antigen and a second antibody binds to the captured antigen. The second antibody makes antigen verification possible and amplifies the signal. Pure SEB as well as SEB in spiked foods (milk and meat) were detected with little interference from the food matrix. In the control experiments with uncontaminated food samples no significant signal was detected. The SPR biosensor assay detects SEB at approximately10 ng/ml rapidly, with initial binding within 2 min. The entire measurement cycle (including washing and chip regeneration) may take 5 min using one antibody or 8 min using two antibodies. These results suggest that the SPR biosensor may be a useful tool for real-time analysis of toxin in foods.

Animals↗

PubMed2005

Determination of priority pesticides in baby foods by gas chromatography tandem quadrupole mass spectrometry.

A gas chromatography-tandem quadrupole mass spectrometry (GC-MS/MS) method for the determination of twelve priority pesticides, and transformation products (e.g. metabolites) specified in the EU Baby Food Directive 2003/13/EC is described. Prior to GC-MS/MS analysis, co-extractives were removed from acetonitrile extracts using dispersive solid phase extraction with octadecyl (200 mg) and primary secondary amine (50 mg) sorbents. The clean up proved essential for the satisfactory long-term chromatographic performance during the analysis of a range of representative commercially pre-prepared baby food samples. Extracts spiked with pesticides at 1-8 microg kg(-1), yielded average recoveries in the range 60-113% with relative standard deviations less than 28%.

Gas Chromatography-Mass Spectrometry↗

PubMed2006

Development of automated online gel permeation chromatography-gas chromatograph mass spectrometry for measuring multiresidual pesticides in agricultural products.

An automated online gel permeation chromatography-gas chromatograph mass spectrometer (GPC-GC/MS) was developed for the rapid determination of residual pesticides in agricultural products. Pesticides were extracted from homogenized food samples with acetonitrile and decontaminated via the matrix solid-phase dispersion (MSPD) technique, using a primary secondary amine as sorbent prior to GPC-GC/MS analysis. A slightly modified preparation method and automated GPC step proved useful in minimizing matrix interference. To evaluate the performance of the system, 97 target pesticides were spiked at a concentration of 0.1mg/kg into a range of food types, including potato, cabbage, carrot, apple, orange, cucumber, and rice. A low flow rate of 0.1 mL/min in GPC resulted in a 40-fold reduction in solvent consumption compared with conventional GPC column applications. The combination of MSPD technique and GPC-GC/MS for the analysis of the 97 pesticides can be accomplished within 90 min. Most pesticides were recovered in the range of 70-120%, with relative standard deviation generally less than 10%. The results demonstrate that the method can be successfully applied with acceptable recoveries to a broad range of target pesticides within a diverse range of food types.

Automation↗

PubMed1997

Polar and non-polar heterocyclic amines in cooked fish and meat products and their corresponding pan residues.

Fourteen cooked dishes with their corresponding pan residues were analysed for polar and non-polar heterocyclic amines using HPLC. The choice of foods, including beef, pork, poultry, game, fish, egg and sausages, was based on an investigation of an elderly population in Stockholm participating in an analytical epidemiological case-control study on cancer risks after intake of heterocyclic amines. The food items were prepared using normal household cooking practices, and to reflect the wide range of surface browning of the cooked dishes that would be encountered in this population, four cooking temperatures were used in the range 150-225 degrees C. For all food samples, the total amount of heterocyclic amines formed at 150 degrees C was less than 1 ng/g cooked product, and at 175 degrees C less than 2 ng/g. The highest concentrations of heterocyclic amines were detected in fillet of pork, reindeer meat and chicken breast fried at 200 and 225 degrees C and their corresponding pan residues. The total sum of 2-amino-3,8-dimethylimidazo-[4,5-f]quinoxaline, 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine was about 1 microgram per 100 g portion (including pan residues) for reindeer meat and chicken breast, and between 1.9 and 6.3 micrograms per 100-g portion for fillet of pork. PhIP was the most abundant heterocyclic amine, identified in 73 of 84 samples, and the highest concentration of PhIP, 32.0 ng/g, was found in the pan residue from fillet of pork cooked at 225 degrees C. The non-polar heterocyclic amines 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole and 3-amino-1-methyl-5H-pyrido[4,3-b]indole were detected in the range of 0.5-7.4 ng/g in most foods cooked at 225 degrees C, and also in meat sauce prepared at 200 and 175 degrees C. The other heterocyclic amines tested for: 2-amino-3-methylimidazo-[4,5-f]quinoline, 2-amino-3,4-dimethylimidazo[4,5-f]quinoline, 2-amino-6-methyl-pyrido-[1,2-a:3',2'-d]-imidazole and 2-aminodipyrido-[1,2-a:3',2'-d]imidazole, were present only at very low or non-detectable levels. The low recoveries of the amino-alpha-carbolines 2-amino-9H-pyrido[2,3-b]indole and 2-amino-3-methyl-9H-pyrido[2,3-b]indole made it impossible to quantify them. However, the co-mutagenic substances 1-methyl-9H-pyrido-[3,4-b]indole and 9H-pyrido[3,4-b]indole were detected at levels of about 1-30 ng/g in most of the dishes cooked at 200 and 225 degrees C.

Amines↗

PubMed1995

Long-term oral refeeding of patients with cirrhosis of the liver.

A previous study has shown that malnourished, clinically stable patients with liver cirrhosis are in protein and energy balance at their spontaneous dietary intake and that an improvement in nutritional status cannot be anticipated at this intake (Nielsen et al. 1993). In the present study we examined to what extent oral intake could be increased by nutritional support, and to what extent dietary protein would be retained with increased intake. The techniques used for balance studies were also validated since this information is not available for patients with liver cirrhosis. Fifteen malnourished patients with alcoholic liver cirrhosis were given increasing amounts of a balanced ordinary diet for 38 (SE 3) d. Intakes of protein and energy were recorded by weighing servings and leftovers on food trays. Protein intake was calculated from food tables. Total N disposal was calculated after measurement of urinary N excretion, and protein balance was calculated from the N balance. A validation study of protein balance in a subgroup of patients (analysis of N in food by the duplicate portion technique, correction for incomplete recovery of urine by measurement of urinary para-aminobenzoic acid (PABA) after administration of PABA tablets, and measurement of faecal N) did not change protein balance values. Protein intake increased from 1.0 (SE 0.1) g/kg per d to 1.8 (SE 0.1) g/kg per d. With increasing protein intake, 84 (SE 8)% of the increase in intake was retained. The rate of protein retention was not saturated at the intakes obtained in this study. Protein intolerance was only encountered in one patient. Available evidence indicates that the requirement for achieving N balance is increased in these patients but protein retention is highly efficient with increased intake. Protein retention is dependent on energy balance. Energy intake was calculated from food tables and total energy expenditure was calculated by the factorial method. A validation study was performed in a subgroup of patients. The energy contents of food sampled by the duplicate portion technique, and of urine and faeces were measured by bomb calorimetry. Resting energy expenditure (REE) was measured by indirect calorimetry before and at the end of the study, and O2 uptake during bicycle exercise was measured before and at the end of the study. The measured intake of metabolizable energy was on average 13% lower than the value given in food tables. Calculated energy expenditure was not changed by the validation study.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary Proteins↗

PubMed2004

Flow-through spectrophotometric sensor for the determination of saccharin in low-calorie products.

A simple, rapid and inexpensive monoparameter flow-through sensor has been developed for the determination of saccharin in low calorie and dietary products. The method is based on the transient adsorption of the sweetener on Sephadex G-25 solid phase packed to a height of 20 mm in the flow cell. The optimal transient retention of the synthetic sweetener, in terms of sensitivity and sampling frequency, was obtained when pH 2.75 citric acid-sodium citrate buffer 5 x 10(-3) M was used as a carrier at a flow-rate of 1.5 ml min(-1). Saccharin was determined measuring its intrinsic absorbance at 217 nm at its residence time. Calibration graphs for peak height and peak area were linear over the range 5.0-200.0 microg ml(-1), RSD 1.18%, and 1.0-200.0 microg ml(-1), RSD 0.78%, respectively. Saccharin was determined in several food samples measuring height or area peak, obtaining recoveries ranging between 98-104 and 99-102% for height and area peak, respectively. The procedure was validated for use in the determination of saccharin in low calorie and dietary products giving reproducible and accurate results.

Beverages↗

PubMed1995

Culture media for the isolation of campylobacters.

The history of the development of selective media for isolation of campylobacters, including the rationale for choice of selective agents is described. Developments have included modifications to allow incubation at 37 degrees C instead of 42 or 43 degrees C and changes in the types and concentrations of antibiotics in order not to inhibit organisms such as Campylobacter upsaliensis, C. jejuni subsp. doylei and some strains of C. coli and C. lari. When examining foods, plating media originally developed for isolation from faeces are normally used, sometimes after liquid enrichment. Most of the media include ingredients intended to protect campylobacters from the toxic effect of oxygen derivatives. Most commonly used are lysed or defibrinated blood; charcoal; a combination of ferrous sulphate, sodium metabisulphite and sodium pyruvate (FBP); and haemin or haematin. To date no medium includes an indicator system--for instance a pH indicator to show whether colonies produce acid or alkali from particular substrates. The manner in which liquid enrichment media are used has been modified for food samples to avoid inhibitory effects on sublethally damaged cells by toxic components in the formula. This is done by a preliminary period of incubation at reduced temperature and sometimes by delayed addition of antibiotics. Expensive and time-consuming methods have been proposed to achieve a microaerobic atmosphere while using liquid enrichment media. To date there is no generally accepted 'standard' method of isolating campylobacters from food.

Anti-Bacterial Agents↗

PubMed2000

Solid phase microextraction/gas chromatography of Salmonella-infected beef.

Eight strains of Salmonellae were incubated in TSB culture medium at 37 degrees C for 24 h. Volatile compounds derived from the bacteria were collected using solid-phase microextraction fibers and then applied to gas chromatography (GC). Similarity analysis of the GC patterns thus obtained could separate these strains on principal component similarity (PCS) scattergrams. Five major food-related pathogenic bacteria and 10 other bacteria (including one Salmonella strain) were also classified by growing in the same medium. It is then proposed to utilize this approach to improve the GC/PCS method of Nakai et al. [Nakai, S.; Wang, Z. H.; Dou, J.; Nakamura, S.; Ogawa, M.; Nakai, E.; Vangerstoep, J. J. Agric. Food Chem. 1999, 47, 576-583] that has been developed for screening safe foods by detecting bacteria contaminated foods. Inoculating food samples pre-enriched through preliminary incubation into a culture medium and then subjecting to the GC/PCS method after secondary incubation enhances the detectability of pathogenic bacteria.

Animals↗

PubMed2002

The correlation method for rapid monitoring of Escherichia coli in foods.

AIMS: A new rapid method was developed to rapidly monitor Escherichia coli counts in foods. MATERIALS AND RESULTS: One ml of modified selective broth with 4-methylumbelliferyl beta-D-glucuronide and 1 ml of food sample were mixed in a sterile test tube and incubated at 37 degrees C. The positive reaction (fluorescence under u.v. light) was monitored at regular 30 min intervals. The positive reaction times in test tubes were compared with actual E. coli numbers from tested samples. The growth of E. coli in test tubes (broth) was much faster than growth on agar. The first experiment was performed to evaluate the rapid correlation method using pure E. coli cultures. The correlation between E. coli counts by the conventional plating method and positive reaction (fluorescence production) times in test tubes was highly agreeable (r(2) = 0 x 95). In the case of low E. coli numbers, such as 2 x 0 log10 cfu ml(-1), the rapid correlation method detected their presence after 10 h incubation. When highly contaminated samples were assayed (8 log10 cfu ml(-1)), the rapid correlation method detected the presence of E. coli after 4 h incubation. In the ground beef experiment, the correlation between fluorescence production time and actual E. coli numbers was also strongly agreeable (r(2) = 0 x 92). CONCLUSIONS: From these results, it is obvious that the new rapid method can rapidly monitor E. coli counts in foods. SIGNIFICANCE AND IMPACT OF THE STUDY: The results indicated that the new method saved about 10-14 h incubation time compared to conventional plating methods. The rapid correlation method required much shorter incubation times compared to conventional plating methods for monitoring E. coli.

Bacteriological Techniques↗

PubMed2004

Characterization of Salmonella enterica serotype Typhimurium isolates from human, food, and animal sources in the Republic of Ireland.

A potential epidemic clone of Salmonella enterica serotype Typhimurium DT104, and the possible emergence of S. enterica serotype Typhimurium DT104b, has been identified from the characterization of 67 S. enterica serotype Typhimurium strains from three sources, human gastroenteritis isolates, isolates from food samples, and veterinary isolates, by antimicrobial resistance profiling, phage typing, and pulsed-field gel electrophoresis. Resistance to ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracycline was found in 77.6% of these strains.

Animals↗

PubMed1998

Enteropathogenic Escherichia coli in raw and cooked food.

A total of 402 Escherichia coli isolates were obtained from a variety of food samples and screened for enteropathogenic E. coli (EPEC). Screening was carried out using 15 specific monovalent antisera from Murex Diagnostic Limited. A total of 19 E. coli isolates were serotyped as EPEC. The EPEC strains were shown to belong to 8 serotypes. Eight out of 19 EPEC strains belonged to serotype 018C:K77 (B21). Seventeen out of 19 of the EPEC strains were isolated from cooked food. The presence of E. coli in cooked food is an indicator of fecal contamination and a sign of unhygienic food handling. The presence of EPEC in food could be a potential source of food-borne outbreak. Hygiene training for every food-handler is a necessity.

Beverages↗