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PubMed2001

Liquid chromatographic determination of the total available free and intrachain lysine in various foods.

A method for the quantitative determination of the total available lysine in various foods is developed. The method is based on the reaction of the amino groups on the lysine molecule with fluorodinitrobenzene and is capable of furnishing simultaneous determination of the available intrachain lysine (known as N-epsilon-[2,4-dinitrophenyl]-L-lysine) or the available free and/or N-terminal lysine (known as N,N'-di-[2,4-dinitrophenyl]-L-lysine). Optimum conditions for separation and quantitation are studied. The results show the proposed method to be both accurate and precise and suitable for food samples containing hydrolyzed proteins.

Chromatography, High Pressure Liquid↗

PubMed1996

Characterization of Listeria monocytogenes isolates by esterase electrophoresis.

Multiple bands of alpha-naphthyl-propionyl esterase (alpha NPE) activity observed following starch gel electrophoresis of cell extracts allowed 219 Listeria monocytogenes isolates from milk, nondairy foods, and clinical and veterinary sources to be assigned to 17 different alpha NPE types. Multilocus enzyme electrophoresis (MEE) analysis was used to obtain electrophoretic mobility data for alpha NPEs and nine other metabolic enzymes; on the basis of these data, the 219 strains were assigned to 59 electrophoretic types. Each of the methods separated the strains into two main groups, and there was extensive agreement on assignment of the strains to the groups. Although the method is less discriminatory than MEE, the usefulness of alpha NPE electrophoresis alone as a rapid, simple typing method for L. monocytogenes for certain purposes is indicated by agreement among alpha NPE, MEE, and restriction fragment length polymorphism types as molecular markers for persistent and transient L. monocytogenes strains found in sequential raw-milk and nondairy food samples obtained from different processors.

Animals↗

PubMed2003

Detection of Shiga toxin-producing Escherichia coli in food.

Shiga toxin-producing Escherichia coli are emerging as a significant source of food-borne infectious disease all over the world. Illness caused by Shiga toxin-producing E. coli can range from self limited, watery diarrhea to life-threatening manifestations such as hemorrhagic colitis, hemolytic uremic syndrome or thrombotic thrombocytopenic purpura and death. Shiga toxin-producing E. coli can potentially enter the human food chain from a number of animal sources, most commonly by contamination of meat with feces or intestinal contents after slaughter or cross-contamination of unpasteurized milk products. Because of the low infectious dose of the O157:H7 Shiga toxin-producing E. coli strain, laboratory diagnosis of Shiga toxin-producing E. coli in food samples has developed a great importance. This review will focus on the microorganism, giving priority to illness prevention and Shiga toxin-producing E. coli detection in food.

Animals↗

PubMed2000

Daidzein and genistein contents of vegetables.

Food samples (n 114) were prepared from vegetables commonly eaten in Europe. The glycosidic forms of the phyto-oestrogens daidzein and genistein were extracted from the dried foods into aqueous methanol. The isoflavones were quantified by GC-MS after hydrolytic removal of any conjugated carbohydrate. Completeness of extraction and any procedural losses of the isoflavones were accounted for using synthetic daidzin (7-O-glucosyl-4'-hydroxyisoflavone) and genistin (7-O-glucosyl-4'5-dihydroxyisoflavone) as internal standards. Of the 114 foods assayed, at a limit of quantification of 0.1 microg/kg dry weight, forty-eight contained no detectable daidzein or genistein, forty-one contained less than 100 microg/kg of the two isoflavones combined and the remaining twenty-five contained more than this amount. Soyabean products contained between 470 and 1420 mg (average of 960 mg) daidzein and genistein combined per kg wet weight of food, and legumes contained between 20 and 5750 microg/kg wet weight of food, with an average of 620 microg/kg. Cooking by boiling in water caused a decrease in the daidzein and genistein content of food in twenty-four of twenty-eight foods. The extent of the decrease was variable and warrants further investigation. The present paper comprises the first comprehensive description of the content of daidzein and genistein in vegetables.

Estrogens, Non-Steroidal↗

PubMedDate not supplied

On-line steam distillation/purge and trap analysis of halogenated, nonpolar, volatile contaminants in foods.

An on-line, steam distillation/purge and trap gas chromatographic procedure is described for determination of halogenated analytes in foods and beverages. Recoveries were generally >80% (versus aqueous standards) from vegetable oil, flour, root beer, cream (10% butter fat), and milk spiked at 1-3 micrograms/kg for each of the 32 analytes studied. Analytes ranged in volatility from vinyl chloride to 1,2,3,4-tetrachlorobenzene. Repeatabilities from aqueous standards were <10% for most analytes. For a 1 g food sample, method detection limits ranged from 0.02 to 0.2 micrograms/kg for the 32 analytes. Reduced recoveries for less volatile analytes, however, occurred when steam-distillable, nonpolar food components were carried to the sparger. This effect was observed for citrus beverages containing steam-volatile limonene, roasted and ground coffees, and some salad dressings. The method was applied to a variety of foods.

Chromatography, Gas↗

PubMed1985

A note on the screening of dried shrimps, shrimp paste and raw groundnut kernels for aflatoxin-producing Aspergillus flavus.

All of 33 samples of dried shrimps, shrimp paste, peanut butter and raw groundnut kernels were contaminated with fungi. Aspergillus and Penicillium spp. were the predominant types in dried shrimps and raw groundnut kernels but no Aspergillus spp. were present in peanut butter or shrimp paste samples. Among 81 Aspergillus isolates obtained from dried shrimps and raw groundnut kernels, 10 were A. flavus/A. parasiticus, of which five were potential aflatoxin-producing A. flavus strains. No aflatoxins were detected in the food samples although some were visibly mouldy and some had high mould counts. The occurrence of aflatoxin-producing strains of A. flavus in dried shrimps and raw groundnut kernels warrants further investigation of these foods and their products as potentially significant sources of aflatoxins.

Aflatoxins↗

PubMed1990

Staphylococcus saprophyticus found to be a common contaminant of food.

The mode of transmission of Staphylococcus saprophyticus, a urinary tract pathogen, was investigated in three related studies. The presence of this organism was sought, during a period of 1 year, in 1331 specimens of various foods, in 920 beef and pork carcasses and on 107 cultures which had been inoculated directly from abattoir workers' protective gloves. Staphylococcus saprophyticus was found to contaminate 16.4% of the various food samples with a high prevalence of 34% in raw beef and pork. It was common in both domestic and imported raw meat products. There was no seasonal variation in the presence of S. saprophyticus in the samples obtained from carcasses. The bacterium was found in 69% of all cultures from the workers' protective gloves. We conclude that S. saprophyticus, originating from slaughtered animals, contaminates food and eventually colonizes the human intestinal tract.

Abattoirs↗

PubMed2004

Tetrachlorodibenzo-p-dioxin in baby food made from chicken produced before and after the termination of ball clay use in chicken feed in the United States.

Polychlorodibenzo-p-dioxin/furans were determined in chicken-containing baby foods collected from an annually conducted total diet survey by the US FDA during the last half of fiscal year (FY) 1997 through the first half of FY 1998. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) was found in 8 of 11 baby food samples. The levels were between 0.025 and 0.28 ng kg(-1) wet wt (0.25-5 ng kg(-1) lipid). The mean TCDD value for chicken-containing baby food with "nondetects" equal to 0 was 1.2 ng kg(-1) lipid, eight times higher than the average level found during a previous survey of chicken lipid TCDD levels in 1996. All other 2,3,7,8-chlorine-substituted dibenzo-p-dioxin congeners were also found with a profile consistent with the use of ball clay in chicken feed. TCDD was not detected in any FY 2000 baby foods made with chicken, with an average limit of detection (LOD) of 0.025 ng kg(-1) wet wt. Whole eggs collected in 1997 from producers that never used ball clay in feed revealed TCDD measurements that were nearly all nondetects and none above the median LOD of 0.015 ng kg(-1) wet wt. The percentage of chickens fed ball clay in their feed was estimated to be between 2.6% and 3.5% of all chickens produced in the United States in 1997.

Aluminum Silicates↗

PubMed2002

A strip liposome immunoassay for aflatoxin B1.

A technique has been developed for the preparation of aflatoxin B1 (AFB1)-tagged liposomes encapsulating a visible dye. These liposomes have several useful potential analytical applications, one of which is demonstrated. A simple plastic-backed nitrocellulose strip is the basis for an assay for detecting AFB1. Samples containing aflatoxin B1 are allowed to migrate by capillary action along the strip into a zone containing immobilized antibodies; then aflatoxin B1-tagged, dye-containing liposomes are allowed to migrate into the same area, filling any remaining antibody sites. The liposomes that bound to the antibody zone exhibit an intense purplish pink color whose optical density is inversely proportional to the aflatoxin concentration in the sample. The device is capable of detecting aflatoxin B1 at levels down to 20 ng and could serve as a rapid procedure for visual screening of agricultural and food samples for AFB1 or, with densitometry, as an inexpensive quantitative assay.

Aflatoxin B1↗

PubMed2006

Simultaneous determination of carbohydrates, carboxylic acids, alcohols, and metals in foods by high-performance liquid chromatography inductively coupled plasma atomic emission spectrometry.

The applicability of the HPLC-ICP-AES coupling for the simultaneous determination of carbohydrates, carboxylic acids, alcohols, and metals in a single chromatographic run has been demonstrated in the present work. Five saccharides, glucose, fructose, sucrose, sorbitol, and lactose; five carboxylic acids, citric, tartaric, malic, lactic, and acetic; and three alcohols, glycerol, ethanol, and methanol, have been determined. A H+ cation exchange column has been used to separate these compounds. The chromatograms have been obtained by monitoring the carbon emission signal at 193.09 nm. The results obtained by HPLC-ICP-AES have been compared against those found with conventional detection systems (i.e., refractive index, UV, and photodyode array detectors). The HPLC-ICP-AES method has shown the following features: (i) organic compounds and metals can be simultaneously determined; (ii) the detection method is universal; (iii) for nonvolatile organic compounds, a complete calibration line can be obtained from a single injection; and (iv) it provides absolute limits of detection similar to or lower than those found with conventional detection systems (i.e., on the order of several tens of nanograms of organic compound). The methodology has been validated through the analysis of food samples such as juices, isotonic beverages, wines, and a certified nonfat milk powder sample.

Alcohols↗

PubMed2003

Polybrominated diphenyl ethers (PBDEs) in foodstuffs: human exposure through the diet.

Polybrominated diphenyl ethers (PBDEs) are used as flame retardants in a variety of materials, including synthetic polymers and textiles. Although these chemicals have been detected in environmental samples and human tissues, there is little information about human exposure to PBDEs through the diet. In the present study, we determined the concentrations of PBDEs in a number of food samples acquired in Catalonia (Spain) during 2000. The dietary intake of PBDEs was estimated for the general population living in this Spanish region. The highest PBDE concentrations were found in oils and fats, fish and shellfish, meat and meat products, and eggs, while the lowest levels corresponded to fruits, vegetables, and tubers. The dietary intake of PBDEs for an adult male was 97.3 ng/day (assuming not detected (ND) = (1)/(2) limit of detection (LOD)) or 81.9 ng/day (assuming ND = 0) The greatest contribution to these values corresponded to fish and shellfish, with approximately one-third of the total intake. TetraBDEs and pentaBDEs were the homologues showing the highest percentages of contribution to the sum of total PBDEs. The comparison of the current dietary intake with the suggested lowest observed adverse effect level value of 1 mg/kg/day for the most sensitive endpoints for toxic effects of PBDEs results in a safety factor over 5 orders of magnitude in relation to PBDE exposure from food.

Adult↗

PubMed1999

Rapid fall in plasma threonine followed by increased intermeal interval in response to first ingestion of a threonine-devoid diet in rats.

In most animals, ingestion of a diet lacking an essential amino acid (EAA) gives rise to anorexia within a few hours. The first signal in this feeding response may be the fall in plasma levels of the limiting EAA. In the present study, we measured plasma amino acid levels and food intake after the first exposure to either a threonine-devoid (THR-DEV) or corrected (COR) diet in 16 rats bearing a chronic jugular catheter for blood sampling. Food intake was reduced 165 min (p<0.05) after presentation of the THR-DEV diet. Analysis of the feeding pattern showed that intake was reduced via a four-fold lengthening of the second inter-meal interval. Plasma threonine levels started to fall between 30 and 60 min after onset of the meal (p<0.05). These results, observed in the same rats, lend further support for an early modification of the plasma amino acid pattern in relation to the decrease in feeding of a diet that is EAA deficient.

Analysis of Variance↗

PubMed2003

Listeria monocytogenes occurrence and characterization in meat-producing plants.

AIMS: The prevalence, level of contamination and epidemiological profile of Listeria monocytogenes were investigated in two meat-producing plants during a 20-month period. METHODS AND RESULTS: Sampling for L. monocytogenes was carried out in a cattle slaughterhouse (n = 72) and a swine meat-processing plant (n = 68) during a 20-month period. Swabs and food samples were analysed with the most probable number (MPN) technique for L. monocytogenes and the isolated strains were characterized by AscI-restriction analysis pulsed-field gel electrophoresis (REA-PFGE). Contamination of meat and meat products was always at low level (below 50 MPN per gram). The seven L. monocytogenes positive samples isolated in the bovine slaughterhouse yielded strains with the same REA-PFGE profile. However, the seven strains isolated in the swine meat processing plant showed six different profiles. Two of them showed indistinguishable profiles with L. monocytogenes strains collected from other meat processing facilities located in the same area. SIGNIFICANCE AND IMPACT OF THE STUDY: The genotyping method is a valuable tool to investigate contamination sources. The study of REA-PFGE profiles indicated that environmental contamination was probably responsible for the persistence of over 16 months of one strain of L. monocytogenes in the cattle slaughterhouse. Several meat suppliers could be responsible for the contamination in the pig meat processing facility, and this is confirmed by the finding of some identical strain in other meat processing facilities located in the same area.

Abattoirs↗

PubMed2000

Isolation and identification of nontuberculous mycobacteria from foods as possible exposure sources.

A variety of foods collected from local supermarkets and produce stands were examined as possible sources of nontuberculous mycobacterial exposure. Food samples were combined with sterile ultrapure water and manually shaken. To remove large particles, the suspensions were filtered through a sterile strainer, centrifuged, and the supernatants were discarded. The food pellets were stored at -75 degrees C. The pellets were treated with either oxalic acid or sodium hydroxide-sodium citrate solutions to reduce contamination by nonmycobacterial organisms. Decontaminated pellets were cultured on both Middlebrook 7H10C agar and Middlebrook 7H10C agar with supplemental malachite green. Plates were observed for growth at 2 and 8 weeks. Isolates demonstrating acid-fastness were identified to species using polymerase chain reaction and restriction enzyme analysis. Nontuberculous mycobacteria (NTM) were recovered from 25 of 121 foods. Six different species of NTM were isolated, the most predominant being Mycobacterium avium.

Animals↗

PubMed1992

Statistical analysis of relationship between net protein utilization in rat and amino acid composition in cooked foods.

To determine the relation between protein nutritive value and amino acid composition of protein in cooked food, statistical analysis was carried out on thirty cooked foods selected from Japanese daily meal. The food samples were cooked, and powdered after freeze-drying. The amino acid composition was determined by liquid chromatography and colorimetry. The Wistar rats were put on the 7% cooked food protein diet and NPU (net protein utilization) was determined. Linear multiple regression analysis was made between NPU and the ratio of individual essential amino acid in the cooked food protein (mg/Ng)/the corresponding amino acid in the reference protein (mg/Ng). The regression equation for the predicted net protein utilization (NPUp) reads as follows: [formula: see text] Highest correlation coefficient (r = 0.93, p < 0.01) was obtained between NPU and NPUp of the protein in the cooked food.

Algorithms↗

PubMed1979

Relative productivity of five selective plating agars for the recovery of Salmonella from selected food types.

During a 3-year period, the relative productivity of brilliant green (BG), bismuth sulfite (BS), Salmonella-Shigella (SS), Hektoen enteric (HE), and xylose lysine, desoxycholate (XLD) agars for recovering Salmonella from 9 food types was determined. Following pre-enrichment, selective enrichment of food samples in tetrathionate broth followed by streaking to BS agar was the single most productive selective enrichment broth-agar combination for recovery of Salmonella in 5 of these food types. A study of the performance of these 5 agars used individually and in various combinations, showed that none of the 5 agars used individually nor any of the possible paired combinations of these agars could be used to satisfactorily detect Salmonella in the 9 food types. The use of all 5 agars was not necessary because one combination of 4 agars (BG, BS, HE, and XLD) recoverd 100% of the Salmonella isolates, as compared with the number of Salmonella isolates recovered by the 5-agar combination, in each food category. This particular 4-agar combination, along with two 3-agar combinations (BG, BS, and XLD agars, and BS, HE, and XLD agars), were each able to recover more Salmonella isolates, than the combination of BG, BS, and SS agars, the combination currently recommended by the AOAC. Finally, the relative costs of using these agars, singly and in various combinations, were determined.

Agar↗

PubMed1988

Changes in water balance and in release of arginine vasopressin during thermal adaptation in guinea-pigs.

The following experiments were made to investigate whether any changes in water balance and in the release of arginine vasopressin (AVP) accompany the development of thermal adaptation. Twelve guinea-pigs (300-400 g initial weight) were kept in individual metabolic cages at 22 degrees C during weeks 1 and 5. During weeks 2-4, six of them were exposed to 5 degrees C, and six to 28 degrees C. Before the start of the experiment, eight animals were implanted with chronic arterial catheters for removal of blood samples. Food and water intake, body weight, and colon temperature, as well as the amounts of urine and feces, were recorded in each animal every morning. In urine and blood plasma samples (taken daily, resp. weekly), the osmolality was estimated by vapor pressure osmometry, and concentrations of AVP by a radioimmunoassay. It is apparent that the daily turnover of water increased from 94 ml in guinea-pigs adapted to 22 degrees C (N), to 111 ml in cold adapted (CA), and to 154 ml in warm adapted (WA) animals. In CA the amounts of AVP excreted in urine increased dramatically (being 10 times higher than in WA). This high release of AVP cannot be explained by changes in osmotic pressure and by alterations in volume of extracellular fluid. It is concluded that AVP is released in CA guinea-pigs mainly as a stressor hormone, in amounts which highly exceed the antidiuretic needs. The WA animals, having free access to water, did not use the AVP system to conserve water. They doubled their water intake, producing more urine of lower osmolality, corresponding to the reduced release of AVP.

Adaptation, Physiological↗

PubMed2005

Development and validation of a solid phase micro-extraction-gas chromatography-mass spectrometry method for the determination of furan in baby-food.

An efficient and simple method for the determination of furan in baby-food (vegetables and fruits) by solid phase micro-extraction-gas chromatography-mass spectrometry (SPME-GC-MS) was developed and validated. Experimental design was used to investigate the effects of temperature and time of extraction. The calculated regression model was used to find the experimental conditions providing the optimal SPME extraction yield. Validation was carried out in terms of limit of detection (LOD), limit of quantitation (LOQ), linearity, precision and trueness. LOD and LOQ values in the low ngkg(-1) were achieved, whereas linearity was established over two order of magnitude. Good precision was obtained both in terms of intra-day repeatability and between-day precision on two concentration levels (RSD% lower than 3.6%). Recovery values of 91.5+/-6.2% and of 96.1+/-1.3% (n=3) were calculated at 75 ngkg(-1) and 75 microgkg(-1) level. Finally, the applicability of the method to the determination of furan in a number of commercial and home-made baby-food samples was demonstrated.

Furans↗