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At least 433 records · Page 24Linked to original sources
PubMed1975

Automated analysis of benzoic acid in food: colorimetric determination after continuous volatilization.

A method is developed to determine benzoic acid colorimetrically with the Technicon AutoAnalyzer. After a selective hydroxylation of benzoic acid by means of hydrogen peroxide and a catalyzing reagent consisting of a buffered solution of cupric ion, catechol and sorbic acid, a reaction follows with 4-aminoantipyrine. The reddish brown reaction product formed is measured at 505 nm. In a distillation unit benzoic acid is continuously separated from the acidified sample stream by volatilization into a stream of nitrogen. With simple manual treatments solid samples can be analysed. Possible interferences caused by naturally present or added compounds in food were investigated. The precision of the method is very good. The coefficient of variation is 0.6% at 50 mug/ml. For several products the recovery was determined with a mean of 98.4%. The working range covered is 0--100 mug benzoic acid/ml.

Benzoates↗
PubMed2005

Quantitative analysis of the response of an electrochemical biosensor for progesterone in milk.

An electrochemical biosensor for progesterone in cow's milk was developed and used in a competitive immunoassay by Hart et al. (1977, Studies towards a disposable screenprinted amperometric biosensor for progesterone, Biosens. Bioelectron. 12, 1113-1121). The sensor was fabricated by depositing anti-progesterone monoclonal antibody (mAb) onto screen-printed carbon electrodes (SPCEs) which were coated with rabbit anti-sheep IgG (rIgG). This sensor was operated following the steps of competitive binding between sample and conjugate (alkaline-phosphatase-labelled progesterone) for the immobilised mAb sites and measurements of an amperometric signal in the presence of p-nitrophenylphosphate using either colorimetric assays or cyclic voltammetry. The hook effect of the progesterone biosensor was found in the concentration range of milk progesterone between 0 and 5 ng/ml when the sensor was fabricated using a loading of 25 ng rIgG per electrode of a diameter of 3 mm and a 1/50 dilution of mAb. A computer model has been developed in this study to simulate the operation of this progesterone biosensor with consideration of the fabrication processes. This paper presents the results of validating the computer model and the model has predicted the hook effect as observed in tests. The model thus reveals that the hook effect is determined by the total number of binding sites available and the rates of labelled and unlabelled progesterone diffusing towards the sensor surface and the binding rates.

Animals↗
PubMed2005

An electrochemical immunosensor for aflatoxin M1 determination in milk using screen-printed electrodes.

The production and assembling of disposable electrochemical AFM1 immunosensors, which can combine the high selectivity of immunoanalysis with the ease of the electrochemical probes, has been carried out. Firstly immunoassay parameters such as amounts of antibody and labelled antigen, buffer and pH, length of time and temperature of each steps (precoating, coating, binding and competition steps) were evaluated and optimised in order to set up a spectrophotometric enzyme-linked immunosorbent assay (ELISA) procedure. This assay exhibited a working range between 30 and 160 ppt in a direct competitive format. Then electrochemical immunosensors were fabricated by immobilising the antibodies directly on the surface of screen-printed electrodes (SPEs), and allowing the competition to occur between free AFM1 and that conjugated with peroxidase (HRP) enzyme. The electrochemical technique chosen was the chronoamperometry, performed at -100 mV. Furthermore, studies of interference and matrix effects have been performed to evaluate the suitability of the developed immunosensors for the analysis of aflatoxin M1 directly in milk. Results have shown that using screen-printed electrodes aflatoxin M1 can be measured with a detection limit of 25 ppt and with a working range between 30 and 160 ppt. A comparison between the spectrophotometric and electrochemical procedure showed that a better detection limit and shorter analysis time could be achieved using electrochemical detection.

Aflatoxin M1↗
PubMed2005

A biosensor based on catalase for determination of highly toxic chemical azide in fruit juices.

In this work, an amperometric biosensor based on catalase enzyme was developed for the determination of azide. The principle of the measurements was based on the determination of the decrease in the differentiation of oxygen level which had been caused by the inhibition of catalase in the bioactive layer of the biosensor by azide. Firstly, the optimum conditions for the inhibitor biosensor were established. In the optimization studies of the biosensor, the most suitable catalase and gelatin amounts and glutaraldehyde ratio were determined. Optimum catalase activity, optimum gelatin amount and glutaraldehyde percentage were 5000 Ucm(-2), 5.94 mgcm(-2) and 2.5%, respectively. Characterization studies of the biosensor such as optimum pH and optimum temperature were carried out. The repeatability experiments were done and the average value (x), standard deviation (S.D.) and variation coefficient (C.V.) were calculated as 98.6 microM, +/-4.16 microM and 4.23%, respectively. A good linear relationship with a correlation coefficient of 0.9902 was obtained over the concentration range of 25 microM to 300 microM azide. After the optimization and characterization studies the proposed biosensor was applied to the determination of azide in certain fruit juices.

Azides↗
PubMed2006

Quantitative and simultaneous detection of four foodborne bacterial pathogens with a multi-channel SPR sensor.

We report the quantitative and simultaneous detection of four species of bacteria, Escherichia coli O157:H7, Salmonella choleraesuis serotype typhimurium, Listeria monocytogenes, and Campylobacter jejuni, using an eight-channel surface plasmon resonance (SPR) sensor based on wavelength division multiplexing. Detection curves showing SPR response versus analyte concentration were established for each species of bacteria in buffer at pH 7.4, apple juice at native pH 3.7, and apple juice at an adjusted pH of 7.4, as well as for a mixture containing all four species of bacteria in buffer. Control experiments were performed to show the non-fouling characteristics of the sensor surface as well as the specificity of the amplification antibodies used in this study. The limit of detection (LOD) for each of the four species of bacteria in the tested matrices ranges from 3.4 x 10(3) to 1.2 x 10(5) cfu/ml. Detection curves in buffer of an individual species of bacteria in a mixture of all four species of bacteria correlated well with detection curves of the individual species of bacteria alone. SPR responses were higher for bacteria in apple juice at pH 7.4 than in apple juice at pH 3.7. This difference in sensor response could be partly attributed to the pH dependence of antibody-antigen binding.

Bacteria↗
PubMed2005

Analysis of acrylamide in food samples by capillary zone electrophoresis.

Conditions for the determination of acrylamide (AA) after derivatisation with 2-mercaptobenzoic acid by capillary zone electrophoresis were established. A derivatisation reagent-acrylamide ratio of 35:1 was selected as optimum and the reagent excess was not removed as it did not affect the determination of acrylamide by CZE. The best separation was achieved using a 40 mM phosphate buffer at pH 8.0, working at 25 kV in un-coated fused silica capillaries. Linear calibration curves over the range studied (0.3-100 microg mL(-1)), the limit of detection (0.07 microg mL(-1)), and both run-to-run (RSD values of 5.8 and 2.2% for concentration at low and medium concentration levels, respectively) and day-to-day precisions (up to 11.2 and 6.7% at low and medium concentration levels, respectively) were established. Finally, the applicability of the CZE proposed methodology was demonstrated by analyzing levels of acrylamide present in different foodstuff products such as home made french fries, breakfast cereals and biscuits.

Acrylamide↗
PubMed2006

Selective analysis of histamine in food by means of solid-phase extraction cleanup and chromatographic separation.

A simple, practical technique is presented for the selective determination and measurement of histamine (HA) levels in fermented food. The method involved a solid-phase extraction cleanup using a Sep-Pak Plus C-18 cartridge and ion-paired reversed-phase high-performance liquid chromatographic (IP-RP-HPLC) separation, followed by detection of HA at its UV absorbance wavelength of 220nm. After evaporating a methanolic extract from the food sample, the resulting residue was reconstituted with 0.2M phosphate buffer (pH 3.0), and subsequently passed through the cartridge. The aliquot of the solution which came out of the cartridge was chromatographed in IP-RP mode on a C-18 column, as the stationary phase, and with a solution of 0.2M phosphate buffer (pH 3.0)-acetonitrile-water (1:24:166, v/v) containing 2mM sodium 1-octane sulfonic acid, as the mobile phase. When this method was applied to a mixture of HA, Cadaverine (Cad), Putrescine (Put), Serotonin (5HT), and Tyramine (Tyr), only HA was detected at 16.4min of retention time. The method was fully validated and validation parameters were: linearity range 2-1000ppm; correlation coefficient >0.991; mean recovery >99.5%; limit of quantification 2ppm and limit of detection 0.5ppm. The method was next applied to 12 brands of Miso (fermented soybean paste), 9 brands of Sake (rice wine), and 5 brands of Shouyu (Japanese soy sauce) to verify its ability to detect the presence of HA in a variety of fermented foods. The method proved to be both rapid and accurate and is therefore recommended for use in HA pollution surveys and in the routine practice of food-quality control.

Chromatography, High Pressure Liquid↗
PubMed2006

Analysis of phytosterols in foods.

Phytosterols are bioactive compounds, one of their most studied and outstanding properties being their cholesterol-lowering activity. This explains the growing interest in the phytosterol contents of foods as either intrinsic or added components. The different steps (extraction, saponification, clean up, chromatographic determination) of plant sterol determination are reviewed, and emphasis is placed on the methods used to assay different phytosterols in food.

Animals↗
PubMed2006

Design of low-frequency ultrasonic sensors for the analysis of the draining stage of cheese production.

This work presents a new ultrasonic system with a transmission mode in the 100-200 kHz frequency range. The system, composed of ultrasonic point sources, is used to monitor the mechanical properties of cheese during the early phases of production. First, our specialized sensor system is presented, and then the results obtained with the system model are compared to the results of actual experiments using the system to monitor the evolution of the medium during draining. The results of a rheological compliance test and shock pulse ultrasonic amplitude measurements agree and correspond quite accurately to the mechanical properties of the evolving physical state of the medium. This method could be used in the future to study the effect on the final cheese quality of the process parameters that interfere with cheese grain consolidation during the draining process.

Cheese↗
PubMed2003

Analysis of acrylamide in food by isotope-dilution liquid chromatography coupled with electrospray ionization tandem mass spectrometry.

A confirmatory method for the determination of low levels of acrylamide in different food products is presented. The method entails extraction of acrylamide with water, precipitation of matrix constituents with acetonitrile, and two clean-up steps consecutively over Isolute Multimode and cation-exchange cartridges. The final extract is analyzed by liquid chromatography (LC) coupled to positive electrospray ionization tandem mass spectrometry employing [13C3]-acrylamide as internal standard. For the chromatographic step, a LC column based on a polymethacrylate gel is employed which shows good retention of acrylamide under isocratic flow conditions (k' = 1.2). Mass spectral acquisition is done by selected reaction monitoring, choosing the characteristic transitions m/z 72-->55, 72-->54 and 72-->27. In-house validation data for breakfast cereals and crackers show good precision of the method, with intra- and interassay variation below 10%. The limits of detection for crackers and breakfast cereals, respectively are estimated at 15 and 20 microg/kg, and recoveries of fortified samples ranged between 58 and 76%. Furthermore, the method is applicable to a number of different food products, including biscuits, crisp bread, wafers, confectionery cocoa liquor, and nuts. Finally, the good results obtained in several small-scale interlaboratory tests provided additional confidence in the performance of the method.

Acrylamide↗
PubMed1997

Coenzyme Q10 in the diet--daily intake and relative bioavailability.

The coenzyme Q10 content of the average Danish diet was estimated from consumption data and from analysis of food items to be 3-5 mg coenzyme Q10 per day, primarily derived (64% of the total) from meat and poultry. To investigate if coenzyme Q10 was absorbed to any significant degree from a food item, a randomized cross-over study with single doses of coenzyme Q10 (30 mg/person), administered either as a meal or as capsules, was carried out in healthy subjects. The serum coenzyme Q10 concentration increased significantly, and the maximum concentrations did not differ significantly for the two forms of administration. The study indicates that coenzyme Q10 is present in food items and absorbed to a significant degree. Thus, dietary coenzyme Q10 may contribute to the plasma coenzyme Q10 concentration.

Animals↗
PubMed1999

Determination of organophosphate and carbamate pesticides in spiked samples of tap water and fruit juices by a biosensor with photothermal detection.

The determination of organophosphate (paraoxon, chlorpyrifos, diazinon) and carbamate (carbaryl, carbofuran) pesticides in spiked drinking water and fruit juices was carried out using a photothermal biosensor. The biosensor consists of a cartridge containing immobilised enzyme acetylcholinesterase (AChE) placed in a flow-injection analysis (FIA) manifold and a photothermal detector based on thermal lens spectrometry. With this approach, 0.2 ng/ml of paraoxon can be detected in less than 15 min. Limits of detection for other organophosphate (chlorpyrifos, diazinon) and carbamate (carbaryl, carbofuran) pesticides varied, depending on their antiacetylcholinesterase (AntiAChE) toxicity, from 1 ng/ml to 4 microg/ml. The biosensor was used for the direct detection of pesticides in spiked tap water and fruit juices without any pretreatment steps. In these cases, the LOD3sigma of 1.5, 2.8 and 4 ng/ml paraoxon in tap water, orange juice and apple juice were obtained, respectively.

Beverages↗
PubMed2006

Separation of Delta5- and Delta7-phytosterols by adsorption chromatography and semipreparative reversed phase high-performance liquid chromatography for quantitative analysis of phytosterols in foods.

A method for the separation, isolation, and identification of phytosterols was developed. A commercial phytosterols mixture, Generol 95S, was fractionated first by adsorption silica gel column chromatography and then separated by means of a semipreparative reverse phase high-performance liquid chromatography fitted with a Polaris C8-A column (250 mm x 10 mm i.d., 5 microm) using isocratic acetonitrile:2-propanol:water (2:1:1, v/v/v) as the mobile phase. Milligram scales of six individual phytosterols, including citrostadienol, campesterol, beta-sitosterol, Delta7-avenasterol, Delta7-campesterol, and Delta7-sitosterol, were obtained. Purities of these isolated sterols were 85-98%. Relative response factors (RRF) of these phytosterols were calculated against cholestanol as an authentic commercial standard. These RRF values were used to quantify by gas chromatography-mass spectrometry (GC-MS) the phytosterols content in a reference material, oils, and chocolates.

Adsorption↗
PubMed2005

Two-stage application of the optimised uncertainty method: a practical assessment.

Uncertainty estimates from routine sampling and analytical procedures can be assessed as being fit for purpose using the optimised uncertainty (OU) method. The OU method recommends an optimal level of uncertainty that should be reached in order to minimise the expected financial loss, given a misclassification of a batch as a result of the uncertainty. Sampling theory can used as a predictive tool when a change in sampling uncertainty is recommended by the OU method. The OU methodology has been applied iteratively for the first time using a case study of wholesale butter and the determination of five quality indicators (moisture, fat, solids-not-fat (SNF), peroxide value (PV) and free fatty acid (FFA)). The sampling uncertainty (s(samp)) was found to be sub-optimal for moisture and PV determination, for 3-fold composite samples. A revised sampling protocol was devised using Gy's sampling theory. It was predicted that an increase in sample mass would reduce the sampling uncertainty to the optimal level, resulting in a saving in expectation of loss of over pounds 2000 per 20 tonne batch, when compared to current methods. Application of the optimal protocol did not however, achieve the desired reduction in s(samp) due to limitations in sampling theory. The OU methodology proved to be a useful tool in identifying broad weaknesses within a routine protocol and assessing fitness for purpose. However, the successful routine application of sampling theory, as part of the optimisation process, requires substantial prior knowledge of the sampling target.

Animals↗