Reveal Listeria 2.0 test for detection of Listeria spp. in foods and environmental samples

A Performance Tested Method validation study was conducted for a new lateral flow immunoassay (Reveal Listeria 2.0) for detection of Listeria spp. in foods and environmental samples. Results of inclusivity testing showed that the test detects all species of Listeria, with the exception of L. grayi. In exclusivity testing conducted under nonselective growth conditions, all non-listeriae tested produced negative Reveal assay results, except for three strains of Lactobacillus spp. However, these lactobacilli are inhibited by the selective Listeria Enrichment Single Step broth enrichment medium used with the Reveal method. Six foods were tested in parallel by the Reveal method and the U.S. Food and Drug Administration/Bacteriological Analytical Manual (FDA/BAM) reference culture procedure. Considering data from both internal and independent laboratory trials, overall sensitivity of the Reveal method relative to that of the FDA/BAM procedure was 101%. Four foods were tested in parallel by the Reveal method and the U.S. Department of Agriculture-Food Safety and Inspection Service (USDA-FSIS) reference culture procedure. Overall sensitivity of the Reveal method relative to that of the USDA-FSIS procedure was 98.2%. There were no statistically significant differences in the number of positives obtained by the Reveal and reference culture procedures in any food trials. In testing of swab or sponge samples from four types of environmental surfaces, sensitivity of Reveal relative to that of the USDA-FSIS reference culture procedure was 127%. For two surface types, differences in the number of positives obtained by the Reveal and reference methods were statistically significant, with more positives by the Reveal method in both cases. Specificity of the Reveal assay was 100%, as there were no unconfirmed positive results obtained in any phase of the testing. Results of ruggedness experiments showed that the Reveal assay is tolerant of modest deviations in test sample volume and device incubation time.     

Validation study to demonstrate the equivalence of a minor modification of Assurance Enzyme Immunoassay method, Official Method 996.14, for detection of Listeria in foods and environmental surfaces to the reference culture methods

The Assurance Enzyme Immunoassay (EIA) for the Detection of Listeria in Foods and Environmental Surfaces, AOAC Official Method 996.14, has been modified to combine the separate antibody and conjugate addition steps into one. A methods comparison study was conducted to demonstrate the equivalence of this modification to the reference culture methods. Two food matrixes and one environmental surface were analyzed. In total, there were valid results from 145 samples and controls. Results showed that the Assurance EIA for Listeria spp. is equivalent to the reference culture methods for the detection of Listeria.     

Nitrosation kinetics of phenolic components of foods and beverages

The kinetics of the reactions between sodium nitrite and phenol or m-, o-, or p-cresol in potassium hydrogen phthalate buffers of pH 2.5–5.7 were determined by integration of the monitored absorbance of the C-nitroso reaction products. At pH > 3, the dominant reaction was C-nitrosation through a mechanism that appears to consist of a diffusion-controlled attack on the nitrosatable substrate by NO⁺/NO₂H₂⁺ ions followed by a slow proton transfer step; the latter step is supported by the observation of basic catalysis by the buffer which does not form alternative nitrosating agents as nitrosyl compounds. The catalytic coefficients of both anionic forms of the buffer have been determined. The observed order of substrate reactivities (o-cresol ≈ m-cresol > phenol ≫ p-cresol) is explained by the hyperconjugative effect of the methyl group in o- and m-cresol, and by its blocking the para position in p-cresol. Analysis of a plot of ΔH^# against ΔS^# shows that the reaction with p-cresol differs from those with o- and m-cresol as regards the formation and decomposition of the transition state. The genotoxicity of nitrosatable phenols is compared with their reactivity with NO⁺/NO₂H₂⁺. © 1997 John Wiley & Sons, Inc.     

Simple and rapid extraction, separation, and detection of alkaloids in beverages

Implementation of an uncomplicated SPE process for the rapid extraction and preconcentration of the alkaloids, colchicine, strychnine, aconitine, and nicotine, from water, apple juice, and nonfat milk samples is presented. When coupled to analysis via micellar EKC (MEKC), the total analysis time per sample was less than 15 min for the water and juice samples and less than 20 min for the milk. The SPE process allowed for anywhere from a three to a fourteen-fold improvement in the LOD for each alkaloid when compared to detecting the alkaloids in a nontreated water sample matrix. Following SPE, the LODs for colchicine, strychnine, and nicotine were sufficient to meet levels from 150 to 5000 times more dilute than the LD(50) for a 50 kg individual drinking 12 oz of a contaminated beverage. Aconitine, on the other hand, was detected at approximately the LD(50) level. The percent recoveries for the SPE ranged from 37% to as high as 99%. Nicotine attained the highest recovery efficiencies, followed by colchicine, and finally, aconitine and strychnine, which were nearly identical. The greatest recovery efficiencies were achieved from apple juice and water, whereas nonfat milk yielded the lowest.     

Liquid chromatographic determination of sugar alcohols in beverages and foods after nitrobenzoylation

Use of p-nitrobenzoyl chloride (PNBC) to form an ultraviolet-absorbing derivative was attempted to determine the sugar alcohols meso-erythritol, xylitol, D-sorbitol, and D-mannitol by liquid chromatography (LC). LC determination of derivatives was performed on an ODS column with acetonitrile-water (65 + 35) as mobile phase. Calibration curves were linear in the concentration range 0.01-100 micrograms/mL. Method sensitivity is 10 to 1000 times higher than that of LC with refractive index detection and gas chromatography with flame ionization detection. Recoveries of sugars added to various foods at 0.1 and 1% ranged from 91 to 102% for meso-erythritol, 75 to 115% for xylitol, 81 to 105% for D-sorbitol, and 81 to 108% for D-mannitol.     

Polymeric membrane ion-selective and cross-sensitive electrode-based electronic tongue for qualitative analysis of beverages

An electronic tongue based on the sensor array of polymeric membrane ion-selective electrodes combined with pattern recognition tools was applied to qualitative analysis of various brands of orange juice, tonic, and milk. The capability of this device to reliably discriminate between different brands of those products was presented. The tests of the system were performed using products of the same brand, but with different manufacture dates (and thus comparable by the term of taste). The fusion of two types of sensors-classical selective ones and partially selective in one versatile array, and working out the sensor array's response by means of principal component analysis and back propagation neural network methods allowed the discrimination between different brands of various beverages with very high accuracy (90-100%). The real performance of the electronic tongue was evaluated applying testing samples from another manufacture lot, than the samples used in the learning set.     

Application of rapid, electrochemical Flash Titration to total acidity and alkalinity determinations in buffers, foods, and beverages

A new technique (Flash Titration) for the determination of total acidity and total alkalinity was applied to food and beverage analysis. Requiring no liquid titrants, Flash Titration is a technique made possible through microfabrication of electrochemical components on a silicon chip. Acidic or basic titrant was generated electrochemically at a noble-metal electrode that intimately surrounded an ion-selective, field-effect transistor pH sensor. As acid or base was generated through electrolysis, sample alkalinity or acidity, respectively, was neutralized in the immediate vicinity of the electrode. Through diffusion, a zone comprising a gradient of partially to totally neutralized sample expanded from the generating electrode into the volume element sensed by the nearby pH sensor. An analysis of the pH signal versus time revealed an end point inflection at an elapsed time related to the total alkalinity or acidity of the sample. End point times were typically a few seconds. In this paper, Flash Titration was applied to the analysis of a variety of samples, including juices, soft drinks, wines, and food products. The differences between the results obtained by the Flash Titration method and a commonly used conventional volumetric method were less than 2% in most food products tested. Analysis costs were reduced both through time saving and reduction or elimination of hazardous liquid titrant disposal, by the use of the Flash Titration method.     

Flow injection analysis of Zn and Co in beverages, biological, environmental and pharmaceutical samples

A new, simple, rapid and selective flow injection analysis (FIA) method for the spectrophotometric quantification (speciation of inorganic and organic form) of Zn and Co with ammonium thiocyanate and malachite green (MG) in the presence of surfactants (CPC and TX-100) is described. The value of apparent molar absorptivity of the Zn- and Co- complexes are (1.23) × 10⁴ and (8.67) × 10³ L mol^–1cm^–1 at absorption maximum, 635 nm, respectively. The detection limit (amount causing a peak height > 3 s) is 15 ppb Zn and 20 ppb Co, whereas their optimum working ranges for the quantitative determinations are 0.05–2.0 ppm Zn and 0.07–2.5 ppm Co in the real samples. The sample thoughput of the method is 120 samples/h at the flow rate of 5.0 mL/min with rel. std. dev. of < ± 1%. The method is free from interferences of almost all ions which are commonly associated with these metals in the complex materials. The composition of the complexes and their reaction mechanism involved are discussed. The effect of FIA and analytical variables for the determination of the metals are optimized. The method has been applied to the quantification of Zn and Co in beverages, biological, environmental, and pharmaceutical samples.     

Reveal Salmonella 2.0 test for detection of Salmonella spp. in foods and environmental samples. Performance Tested Method 960801

Reveal Salmonella 2.0 is an improved version of the original Reveal Salmonella lateral flow immunoassay and is applicable to the detection of Salmonella enterica serogroups A-E in a variety of food and environmental samples. A Performance Tested Method validation study was conducted to compare performance of the Reveal 2.0 method with that of the U.S. Department of Agriculture-Food Safety and Inspection Service or U.S. Food and Drug Administration/Bacteriological Analytical Manual reference culture methods for detection of Salmonella spp. in chicken carcass rinse, raw ground turkey, raw ground beef, hot dogs, raw shrimp, a ready-to-eat meal product, dry pet food, ice cream, spinach, cantaloupe, peanut butter, stainless steel surface, and sprout irrigation water. In a total of 17 trials performed internally and four trials performed in an independent laboratory, there were no statistically significant differences in performance of the Reveal 2.0 and reference culture procedures as determined by Chi-square analysis, with the exception of one trial with stainless steel surface and one trial with sprout irrigation water where there were significantly more positive results by the Reveal 2.0 method. Considering all data generated in testing food samples using enrichment procedures specifically designed for the Reveal method, overall sensitivity of the Reveal method relative to the reference culture methods was 99%. In testing environmental samples, sensitivity of the Reveal method relative to the reference culture method was 164%. For select foods, use of the Reveal test in conjunction with reference method enrichment resulted in overall sensitivity of 92%. There were no unconfirmed positive results on uninoculated control samples in any trials for specificity of 100%. In inclusivity testing, 102 different Salmonella serovars belonging to serogroups A-E were tested and 99 were consistently positive in the Reveal test. In exclusivity testing of 33 strains of non-salmonellae representing 14 genera, 32 were negative when tested with Reveal following nonselective enrichment, and the remaining strain was found to be substantially inhibited by the enrichment media used with the Reveal method. Results of ruggedness testing showed that the Reveal test produces accurate results even with substantial deviation in sample volume or device development time.     

High-performance liquid chromatographic determination of mono-, poly- and hydroxycarboxylic acids in foods and beverages as their 2-nitrophenylhydrazides

The application of direct derivatization in conjunction with high-performance liquid chromatography (HPLC) is described for the determination of both free and total carboxylic acids in foods and beverages. The method is based on the reaction of the carboxylic acids with 2-nitrophenylhydrazine hydrochloride, without complicated isolation steps, which produces their non-volatile hydrazine derivatives. The HPLC of a series of carboxylic acid groups was performed isocratically with short retention times. The analytical results showed good recovery and reproducibility using each internal standard. Due to its excellent selectivity and sensitivity, the present method can serve as a useful tool for routine determinations of mono-, poly- and hydroxycarboxylic acids in foods and beverages.     

Accredited laboratory for detection of irradiated foods in Poland

The history of the development and the role of the Accredited Laboratory for Detection of Irradiated Foods in the national quality food control system are described. The analytical methods for the detection of irradiation in foods adapted and accredited in the Laboratory are enumerated and discussed.     

A site-specific and multi-element isotopic approach to origin inference of sugars in foods and beverages

A strategy is presented for the characterization of sugars according to their botanical origin. The samples fermented in standardized conditions can be described in the multi-dimensional space of the overall carbon isotope ratio of ethanol measured by isotope ratio mass spectrometry (IRMS) and of the specific hydrogen isotope parameters of the methyl and methylene sites derived from nuclear magnetic resonance investigation of site-specific natural isotope fractionation (SNIF-NMR method). In the comparison of natural juices, the deuterium and oxygen-18 parameters of water extracted from the juice and from the end fermentation medium also contain information on the origin of the product. The isotopic effects of the concentration processes leading to concentrated juices, musts and syrups can be estimated and taken into account in interpreting the data.The classification power of this multi-element and multi-site approach is illustrated by discriminant analyses involving selected isotopic variables associated with pineapple, apple and barley sugars, compared to beet and cane sugars which are common sources of enrichment. The ability of the method to detect adulteration by exogeneous sugars is improved when environmental conditions can be taken into account.     

Suitability of the thermoluminescence method for detection of irradiated foods

Irradiated foods can be detected by thermoluminescence (TL) of contaminating minerals. Altogether about 300 lots of herbs, spices, berries, mushrooms and seafood were studied by the TL method. Irradiated herbs and spices were easily differentiated from unirradiated ones two years after irradiation of a 10 kGy dose. The mineral composition of seafood was variable; and while calcite was suitable for the TL analysis, aragonite and smectite gave unreliable results. Control analyses during two years confirmed the reliability of TL method.     

SDIX RapidChek Listeria F.A.S.T. environmental test system for the detection of Listeria species on environmental surfaces

The SDIX RapidChek Listeria F.A.S.T. test system was validated against the U.S. Department of Agriculture-Food Safety and Inspection Service (USDA-FSIS) cultural reference method for the detection of Listeria species on stainless steel, plastic, rubber, and painted concrete. The SDIX method uses a proprietary RapidChek Listeria enrichment media for a one-step, 24-40 h enrichment at 30 degrees C, and detects Listeria on an immunochromatographic lateral flow device in 10 min. Different Listeria species were used to spike each of the environmental surfaces. Environmental surfaces were spiked at levels ranging from 50 to 400 CFU/surface (1 in.2 swabs for painted concrete, 4 in.(2) for sponge). A total of 120 spiked samples were tested by the SDIX method at 24 and 40 h and the cultural reference method. Total confirmed positives were 49, 54, and 48 for the SDIX 24 h method, the SDIX 40 h method, and the USDA-FSIS cultural reference method, respectively. Nonspiked samples from all environmental surfaces were reported as negative for Listeria spp. by all methods. The overall Chi square was 0.017 (P = 0.104) and 0.611 (P= 0.566) after a 24 and 40 h enrichment, respectively, indicating that the test method was equivalent in performance to the reference method at both enrichment times. The SDIX method was evaluated for the detection of 50 Listeria and 35 non-Listeria bacterial strains. All 50 Listeria strains were detected by the method (100% sensitivity). Five out of 35 non-Listeria species gave light test signals when grown in nonselective broth culture and tested undiluted. However, when grown in the RapidChek Listeria F.A.S.T. proprietary media, only one bacterial strain (Staphylococcus aureus) was detected, giving a very low test signal (97% specificity). The method was shown to be robust toward several alterations in testing and storage conditions.     

Design, synthesis, and characterization of nucleic-acid-functionalized gold surfaces for biomarker detection

Nucleic-acid-functionalized gold surfaces have been used extensively for the development of biological sensors. The development of an effective biomarker detection assay requires careful design, synthesis, and characterization of probe components. In this Feature Article, we describe fundamental probe development constraints and provide a critical appraisal of the current methodologies and applications in the field. We discuss critical issues and obstacles that impede the sensitivity and reliability of the sensors to underscore the challenges that must be met to advance the field of biomarker detection.     

Surface-enhanced Raman scattering for quantitative detection of ethyl carbamate in alcoholic beverages

Ethyl carbamate, a by-product of fermentation and storage with widespread occurrence in fermented food and alcoholic beverages, is a compound potentially toxic to humans. In this work, a new approach for quantitative detection of ethyl carbamate in alcoholic beverages, based on surface-enhanced Raman scattering (SERS), is reported. Individual silver-coated gold nanoparticle colloids are used as SERS amplifiers, yielding high Raman enhancement of ethyl carbamate in three kinds of alcoholic beverages (vodka, Obstler, and white rum). The characteristic band at 1,003 cm^-1, which is the strongest and best reproducible peak in the SERS spectra, was used for quantitative evaluation of ethyl carbamate. The limit of detection, which corresponds to a signal-to-noise ratio of 3, was 9.0?×?10^-9 M (0.8 μg?·?L^-1), 1.3?×?10^-7 M (11.6 μg?·?L^-1), and 7.8?×?10^-8 M (6.9 μg?·?L^-1), respectively. Surface-enhanced Raman spectroscopy offers great practical potential for the in situ assessment and identification of ethyl carbamate in the alcoholic beverage industry.     

Micro- and nanomechanical sensors for environmental, chemical, and biological detection

Micro- and nanoelectromechanical systems, including cantilevers and other small scale structures, have been studied for sensor applications. Accurate sensing of gaseous or aqueous environments, chemical vapors, and biomolecules have been demonstrated using a variety of these devices that undergo static deflections or shifts in resonant frequency upon analyte binding. In particular, biological detection of viruses, antigens, DNA, and other proteins is of great interest. While the majority of currently used detection schemes are reliant on biomarkers, such as fluorescent labels, time, effort, and chemical activity could be saved by developing an ultrasensitive method of label-free mass detection. Micro- and nanoscale sensors have been effectively applied as label-free detectors. In the following, we review the technologies and recent developments in the field of micro- and nanoelectromechanical sensors with particular emphasis on their application as biological sensors and recent work towards integrating these sensors in microfluidic systems.