SEARCH · PubMed Health

Results for “Food samples”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,171 records · Page 65Linked to original sources

PubMedDate not supplied

Effects of restricted food intake on neutral lipid and free fatty acid levels in the digestive gland-gonad complex and faeces of Biomphalaria glabrata (Gastropoda).

High-performance thin-layer chromatography (HPTLC) was used to determine neutral lipids and free fatty acids in the digestive gland-gonad complex (DGG) and faeces of Biomphalaria glabrata. Three populations of B. glabrata were given varying food intakes for one week. They were either unrestricted (lettuce ad libitum plus a weekly feeding of Tetramin), restricted (15-17 mg of lettuce every two days), or starved (no food). Samples were prepared by extraction in chloroform:methanol (2:1), followed by a Folch wash (0.88% aqueous KCl). The major lipids detected in the DGG were triacylglycerols, free fatty acids and free sterols. Free fatty acids and free sterols were the major lipids detected in the snail faeces. Analysis by TLC-densitometry showed a statistically significant difference in the DGG levels of triacylglycerols and free sterols between the unrestricted and restricted groups, as well as between unrestricted and starved groups. Analysis of faecal samples revealed a significant difference in free fatty acids between unrestricted and starved groups on the seventh day.

Animals↗

PubMed2002

Hydrophilic and lipophilic antioxidant activities of grapes.

The 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid)/H2O2/horseradish peroxidase (ABTS/H2O2/HRP) decoloration method permits the evaluation of the antioxidant activity of complex food samples. This method is capable of determining both hydrophilic (in buffered media) and lipophilic (in organic media) antioxidant properties in the same sample. Its application to the study of the antioxidant properties of grapes, one white and two black, has permitted us to establish important differences in the antioxidant activity. The black grapes showed higher antioxidant activity than the white variety. The determination of hydrophilic antioxidant activity (HAA) and lipophilic antioxidant activity (LAA) in the three grapes showed that a minor contribution (4-13%) of total antioxidant activity (TAA) was due to LAA in all cases. The experimentally determined HAA could be approximated using the relative contributions of the calculated values of reference compounds (total phenols as gallic acid and anthocyanins as malvidin).

Anthocyanins↗

PubMedDate not supplied

Studies and application of catalytic kinetic spectrophotometric determination of trace chromium(VI) sensitized by microemulsion medium.

A new catalytic kinetic spectrophotometric method for the determination of trace amount of chromium (VI) in microemulsion medium has been developed. The method is based on the catalytic effect of chromium (VI) on the oxidation of nuclear fast red in the presence of Tween-80 microemulsion and HAc-NaAc buffer solution (pH = 5.2). The linear ranges are in the range of 0 approximately 0.0480 microg mL(-1) of Cr (VI) at 528 nm and the detection limit is 1.56x10(-9)g mL(-1). The method has been applied in determination of Cr (VI) in water and food samples with satisfactory results. The relative standard deviation is less than 4.6 % and the recovery is 93.5 approximately 104 %.

Acetic Acid↗

PubMedDate not supplied

Menopausal experiences and bone density of Mayan women in Yucatan, Mexico.

This cross-sectional study reports on the menopausal transition of Mayan women from Yucatan, Mexico. A total of 228 women completed the study, and 118 women were classified by history as postmenopausal; the others were premenopausal. Demographic information, reproductive history, physical examination, hormone concentrations, radial bone density, food samples, and history of physical activity were obtained. The average age at which menopause occurred by history was 44.3 +/- 4.4 years; this is reflected in the distribution of FSH levels by age. None of the women reported symptoms of hot flashes, and none recalled any history of significant symptoms associated with their menopausal transition. Hormone levels were similar to U.S. reference values with elevated FSH (66.6 +/- 29.1 mIU/ml), low estradiol (9.4 +/- 8.3 pg/ml) and estrone (13.3 +/- 7.8 pg/ml), E1 > E2, and normal levels of testosterone and androstenedione. BMD declined with age, and values were lower than reference values for United States women. Clinical evidence of fracture was not detected by history or physical examination even for those who were 20 years postmenopausal. The endocrine characteristics of menopause among Mayan women in Yucatan are similar to hormonal changes reported for women in the United States, but signs, symptoms, and apparent consequences are different in the two populations.

Adult↗

PubMed2006

Sensitive determination of carbohydrates labelled with p-nitroaniline by capillary electrophoresis with photometric detection using a 406 nm light-emitting diode.

p-Nitroaniline was explored as a derivatising reagent for UV absorbance detection of carbohydrates after separation by CE. This derivatising agent has three advantages: first, it has excellent water solubility; second, it has high molar absorptivity; and third, it is possible to obtain sensitive detection using a UV or blue light-emitting diode (LED) as the light source. The labelling reaction took less than 30 min to complete with high reaction yield. The separation process was modelled and optimised using an artificial neural network. Nine carbohydrates were separated by a CE system within 16 min using a 0.17 M boric acid buffer at pH 9.7. On-column LED detection at 406 nm allowed the detection of carbohydrates with good detection limits (<1.1 microM or 8.8 fmol) and reproducible quantification in the concentration range of 2.6-200 microM. This method was applied successfully to the determination of component carbohydrates in some food samples.

Aniline Compounds↗

PubMed2006

Feasibility of gas chromatography--ion trap tandem mass spectrometry for the determination of polychlorinated biphenyls in food.

The different parameters affecting the ionisation and fragmentation of selected polychlorinated biphenyls (PCBs) in an IT detector working in the MS/MS mode, ITD(MS/MS), have been optimised for maximum selectivity and sensibility. The low LODs (in the range 0.03-0.3 microg/L), the satisfactory repeatability (RSDs in general below 11%) and reproducibility (RSDs below 17%) obtained when analysing standard solutions ensured proper determination of the PCBs studied at the concentrations typically found in food samples. Foodstuffs naturally contaminated with varying levels of PCBs have been analysed using the optimised GC-ITD(MS/MS) method. The results obtained compared favourably with those found using more conventional detectors, such as (micro-)electron capture detection (for ortho-PCBs) and high-resolution MS (for non-ortho-PCBs), as well as with the consensus PCB levels established for these particular samples via an international interlaboratory exercise. The relative merits of these three detectors have been discussed.

Journal Article↗

PubMed2006

Multiplex PCR-based detection of potential fumonisin-producing Fusarium in traditional African vegetables.

Culture-independent methods employed in fungal genetic studies using in vitro amplification (PCR) and analysis of specific genes or gene fragments have proved to be useful for detection, identification, and molecular taxonomy of various plant pathogens including Fusarium spp. This approach may be faster than culture-dependent methods, and could especially be of value for the rapid detection of slow-growing toxin-producing species in food samples. The present study was aimed at the development and evaluation of multiplex PCR-based methods for the detection and identification of potential fumonisin-producing Fusarium spp. in traditional morogo-leafy vegetables supplementing the maize-based staple diet of rural communities in South Africa. In these rural subsistence settings, some morogo plants grow as weeds in maize fields where they might become contaminated with potential fumonisin-producing Fusarium strains before being collected for consumption. Substances released by senescent vegetables could induce toxin production during storage. Using fumonisin-positive MRC Fusarium verticillioides strains as reference cultures, the following primer sets for the detection of specific gene fragments in fumonisin-positive Fusarium spp. were evaluated: (i) the conserved transcription elongation factor gene (EF-1), (ii) the FUM1 gene encoding polyketide synthase for fumonisin B1 production, and (iii) 18S rRNA gene. Preliminary results indicated that, these DNA fragments were amplified from MRC reference strains as well as Fusarium spp. isolated from morogo. The annealing temperature for the multiplex PCR was 55 degrees C and each reaction contained 25 pmol of each of the primer sets EF and FUM1 and 12.5 pmol of the 18S primer set. The detection limit of the individual primers was up to 1 ng and for the multiplex up to 10 ng. This demonstrates the potential of this method for the detection of potential fumonisin-positive strains.

Fumonisins↗

PubMed1999

Electrospray ionization-tandem mass spectrometry for the analysis of tryptophan derivatives in food.

Our knowledge about bioactive tryptophan derivatives in the diet is rather limited. Consequently, our attention was focused on the efficient profiling, i.e. the structure specific detection, of novel tetrahydro-beta-carbolines and tryptophan glycoconjugates in food samples. Applying HPLC-MS/MS for screening and structural characterization, numerous products derived from the reaction of tryptophan with alpha-oxo acids and carbohydrates could be identified by means of neutral loss scanning. Subsequently, product ion experiments followed by the synthesis of the respective reference compounds accomplished structure elucidation of tryptophan derivatives.

Carbolines↗

PubMed1990

Restriction endonuclease analysis of chromosomal DNA from Listeria monocytogenes strains.

Restriction endonuclease analysis of chromosomal DNA was applied to thirteen Listeria monocytogenes strains alongside the more conventional typing methods of serotyping and phage typing. The organisms were isolated from cases of sporadic listeriosis (nine strains); from an occasional nosocomial cluster (two strains); and from food samples (two strains). Purified DNAs were digested with EcoRI restriction endonuclease, and restriction fragments separated by electrophoresis. Restriction patterns correlated well with phage patterns, but also allowed typing of the phage-untypable strains. DNA fingerprinting appears to be a potentially helpful tool for epidemiological investigations of listeric infections, particularly when phage typing fails to determine the identity or diversity of the isolates.

DNA Fingerprinting↗

PubMed1993

A combined polymerase chain reaction-colour development hybridization assay in a microtitre format for the detection of Clostridium spp.

We have developed a rapid and sensitive assay for the detection of clostridial cells or spores in liquid food samples. The method recognizes Clostridium 16S (small ribosomal subunit RNA) rDNA (ribosomal DNA) sequences by a polymerase chain reaction-digoxigenin-labelling protocol, coupled to a capture oligonucleotide immobilized on a microtitre plate. The positive results are revealed by means of a colour reaction. In 6 h of non-intensive labour, we can detect as few as two to five clostridial cells or spores in experimentally contaminated soft drinks.

Bacteriological Techniques↗

PubMed1983

Effect of thermal treatments on immunoreactivity and proteolytic activity of papain.

Thermal treatment of papain affects somewhat less its immunoreactivity than its proteolytic activity, especially when higher temperatures and longer heat exposures are applied. Immunochemical methods seem to be, in this respect, more advantageous for papain determination in thermally processed food samples (e.g. pasteurized beer) than assays of proteolytic activity. The proteolytic activity is substantially influenced by the type of substrate used. The following substrates affect the proteolytic activity of partly inactivated papain in an increasing order: low-molecular weight substrate BAPA (N alpha-benzoyl-D, L-arginine-p-nitroanilide) less than HPA (hide powder azure) less than hemoglobin. A protective effect of albumin on papain thermoinactivation was found using both immunochemical and proteolytic activity assays.

Antigens↗

PubMed1994

Zinc bioavailability and tea consumption. Studies in healthy humans consuming self-selected and laboratory-controlled diets.

One self-selected study (study A) and one laboratory-controlled study (study B) were conducted to investigate the effect of tea consumption on zinc bioavailability in healthy humans. The 14-day study A consisted of two 7-day experimental periods, while the 28-day study B consisted of two 14-day experimental periods. In study A eight subjects and in study B ten subjects were participated. Subjects of study A consumed self-selected diets and kept a record of foods eaten. In study B, subjects ate a constant and weighted laboratory controlled diet. In both studies, subjects consumed 8 g of instant tea during tea supplementation periods. Complete urine and fecal collections were made by subjects of both studies. Zinc contents of urine, fecal and food samples were determined by using Atomic Absorption Spectrophotometer. Mean zinc intakes of humans consuming self-selected diets were below the RDA. Mean urinary zinc excretion, fecal zinc excretion and zinc balance were unaffected by the tea consumption. Negative zinc balances in study A and positive zinc balances in study B were observed in both tea and no tea dietary treatments. Tea consumption showed a small but not statistically significant adverse affect on zinc bioavailability in humans.

Adult↗

PubMed2004

Evaluation of the results from an inter-laboratory comparison study of the determination of acrylamide in crispbread and butter cookies.

Analytical methods currently employed for determination of acrylamide (AA) in two carbohydrate-rich food samples, crispbread and butter cookies, obtained commercially, and native and spiked bread extract samples have been evaluated in a collaborative study. The objective of the study was to obtain information about the performance of the participating laboratories when analysing samples with an AA content close to the limit of quantification ( LOQ) and at a higher AA level, and to investigate the influence of sample-preparation procedures on the results of the analysis. For this purpose an aqueous native extract of white bread crumb, a fortified extract, and AA standard solutions, the analyte content of which were not disclosed to the participants, were included in the study. A total of 62 laboratories, applying seven different measurement techniques and a broad spectrum of analyte extraction and sample-preparation procedures reported their analytical results. Because the measurement data were not normally distributed, they were evaluated by application of robust statistics. The relative performance of the laboratories was highlighted by calculation of z-scores. For the crispbread sample, especially, a large percentage of the calculated z-scores were outside the satisfactory range. From their distribution it became obvious that one of the analytical techniques might be biased, if not applied correctly. Consequently, the impact of the applied methods was examined in more detail. Information about the analytical technique, extraction solvent, quantity weighed, calibration method, clean-up, and the experience of the participating laboratories were extracted from the analytical protocols and transcribed into a data matrix which was evaluated by multifactor analysis of variance. The applied measurement technique seems to have a statistically significant influence on the analytical results.

Journal Article↗

PubMed2005

Separation and determination of sugars by reversed-phase high-performance liquid chromatography after pre-column microwave-assisted derivatization.

In this study the possibility of derivatizing sugars using microwave irradiation was investigated. The amount of reagent, irradiation intensity, and derivatization time were optimized. In the derivatization of sugars with p-nitroaniline the reaction is complete within 5 min at 600 W when the p-nitroaniline-to-sugar and NaBH3CN-to-sugar mole ratios were above 1.4 and 3.1, respectively. A Doehlert design was used to optimize the mobile phase for separation of p-nitroaniline-labeled sugars; and the best separation was obtained by use of 0.01 mol L-1 acetate buffer at pH 4.40 containing 11.0% acetonitrile. Analysis using this method was highly sensitive and analysis time was short. Finally, a food sample was analyzed using the proposed method.

Journal Article↗

PubMed2005

A dynamic continuous-flow dialysis system with on-line electrothermal atomic-absorption spectrometric and pH measurements for in-vitro determination of iron bioavailability by simulated gastrointestinal digestion.

A dynamic continuous-flow dialysis (CFD) method with on-line electrothermal atomic absorption spectrometric (ETAAS) and pH measurements for study of simulated gastrointestinal digestion has been developed for prediction of iron bioavailability. The method used to estimate mineral bioavailability was based on gastric digestion in a batch system then dynamic continuous-flow intestinal digestion. The intestinal digestion was performed in a dialysis bag placed inside a chamber containing a flowing stream of dialyzing solution. Mineral concentration and dialysate pH were monitored by ETAAS and use of a pH meter, respectively. The amount of dialyzed minerals in the intestinal digestion stage was used to evaluate the dialyzability. The dialysis profile and pH change can be used to understand or examine differences between the dialyzability of different food samples. To test the proposed system it was used to estimate the iron dialyzability of different kinds of milk. Iron dialyzability for powdered cow milk, cereal milk, and two brands of soymilk was found to be 1.7, 20.4, 24.9, and 37.7%, respectively. The developed CFD-ETAAS-pH system is a simple, rapid, and inexpensive tool for bioavailability studies, especially for minerals at ultratrace levels.

Animals↗

PubMed1996

Automatic determination of total aliphatic amines by on-line photometric liquid-liquid microextraction.

An automatic flow method for the determination of total aliphatic amines has been developed. Using an integrated micro extraction unit at the detection point that allows continuous on-line monitoring of small organic plug from which amines are extracted. It is based on the formation of ion-pairs between aliphatic amines and sodium 1,2-naphthoquinone-5-sulphonate that are subsequently extracted into chloroform. The gradual enrichment of the organic phase with the ion-pair is continuously monitored at 460 nm. Absorbance readings at a fixed time and the slopes of absorbance-time recordings are the measured parameters used for determination purposes. The proposed method has been applied to the determination of total aliphatic amines in both synthetic and real (food) samples.

Journal Article↗

PubMed2005

Rapid purification of recombinant listeriolysin O (LLO) from Escherichia coli.

Listeria monocytogenes is an emerging foodborne pathogen that is responsible for about 28% of the food-related deaths in the United States. It causes meningitis, septicaemia and in pregnant women, abortions and stillbirths. It secretes the toxin listeriolysin O (LLO) that allows the bacteria to enter the cytoplasm of host cells, where they can replicate and cause further infection. The rapid and sensitive detection of LLO in food samples is a key to monitoring and prevention of listeriosis. To facilitate the development of an assay for the specific detection of LLO, a source of LLO is essential. We outline a method of producing a large amount of functional LLO by expressing the hlyA gene (encoding LLO) in Escherichia coli and purifying the recombinant LLO using a one-step purification method. Purification of the protein takes only about 4 h. We compared three different expression constructs for the production of the toxin, which tends to interact strongly with a number of column surfaces. The first construct, using an intein fusion system, could not be purified from the column. The second LLO construct contained an N-terminus His tag; it gave a yield of 3.5-8 mg l(-1). The third contained a C-terminus His tag; it gave a yield of 2.5 mg l(-1) LLO. The purified LLO from the latter two constructs retained its activity at 4 degrees C for over a year as determined by bovine red blood cell hemolysis assay. This paper provides a much-needed, high-yield, one-step purification method of recombinant LLO, and is the first to provide evidence of long-term stability of the toxin for further applications.

Bacterial Toxins↗

PubMed1999

Preparation, separation, and confirmation of the eight geometrical cis/trans conjugated linoleic acid isomers 8,10- through 11,13-18:2.

Conjugated linoleic acid (CLA) mixtures were isomerized with p-toluenesulfinic acid or I2 catalyst. The resultant mixtures of the eight cis/trans geometric isomers of 8,10-, 9,11-, 10,12-, and 11,13-octadecadienoic (18:2) acid methyl esters were separated by silver ion-high-performance liquid chromatography (Ag+-HPLC) and gas chromatography (GC). Ag+-HPLC allowed the separation of all positional CLA isomers and geometric cis/trans CLA isomers except 10,12-18:2. However, one of the 8,10 isomers (8cis, 10trans-18:2) coeluted with the 9trans,11cis-18:2 isomer. There were differences in the elution order of the pairs of geometric CLA isomers resolved by Ag+-HPLC. For the 8,10 and 9,11 CLA isomers, cis,trans eluted before trans,cis, whereas the opposite elution pattern was observed for the 11,13-18:2 geometric isomers (trans,cis before cis,trans). All eight cis/trans CLA isomers were separated by GC on long polar capillary columns only when their relative concentrations were about equal. Large differences in the relative concentration of the CLA isomers found in natural products obscured the resolution and identification of a number of minor CLA isomers. In such cases, GC-mass spectrometry of the dimethyloxazoline derivatives was used to identify and confirm coeluting CLA isomers. For the same positional isomer, the cis,trans consistently eluted before the trans,cis CLA isomers by GC. High resolution mass spectrometry (MS) selected ion recording (SIR) of the molecular ions of the 18:1, 18:2, and 18:3 fatty acid methyl esters served as an independent and highly sensitive method to confirm CLA methyl ester peak assignments in GC chromatograms obtained from food samples by flame-ionization detection. The high-resolution MS data were used to correct for the nonselectivity of the flame-ionization detector.

Chromatography, Gas↗