Cross-Reactivity of Chili Peppers (Capsicum sp.) with the xMAP Food Allergen Detection Assay

The xMAP food allergen detection assay (xMAP FADA) is an advanced multiplex immunoassay with multiple antibodies for each of 15 target food allergens and gluten, allowing for signal confirmation and antigenic profiling to occur in a single analysis. Botanicals used as spices are complex matrices for allergen analysis because they can exhibit inherent cross-reactivity with antibodies employed by the assays. Preliminary examinations of botanicals revealed chili peppers to have notably high levels of cross-reactivity with Brazil nut and hazelnut antibody bead sets in the xMAP FADA. This in-depth investigation of 29 pre-ground and whole chili peppers indicated Brazil nut and hazelnut cross-reactivity to be consistent among most members of genusCapsicum, although cross-reactive signals generated by chili peppers were distinguishable from signals indicative of target allergen detection. Using the requirements that complementary antibodies used in the assay generated positive responses and that the various secondary end points were characteristic of the target analytes, xMAP FADA reactivity to chilis of the genus Capsicum was categorized as cross-reactivity instead of confirmed detection of target allergenic foods.

Multiplex-Competitive ELISA for Detection and Characterization of Gluten during Yogurt Fermentation: Effects of Changes in Certain Fermentation Conditions on Gluten Protein Profiles and Method Reproducibility Assessment

The protein/peptide profiles of gluten during yogurt fermentation were evaluated using an optimized multiplex-competitive ELISA by preparing yogurts incurred with gluten at different concentrations and by varying certain fermentation conditions. Analysis indicated that epitope-specific responses with antibody binding to glutenin epitopes decreased less during longer fermentation times or at higher starter culture concentrations relative to gliadins. Incomplete proteolysis was observed after 24 h of fermentation, which became more efficient as fermentation time was increased. Western blot confirmed the results of ELISA. Cluster analysis indicated that out of the investigated parameters, fermentation time is the only parameter that could affect the overall gluten protein/peptide profiles during yogurt fermentation. This parameter needs consideration in evaluating the suitability of calibrant(s) to be used with the multiplex-competitive ELISA or any other methods to ensure accurate quantitation of gluten in yogurts and potentially in other foods with similar fermentation chemistry. A small-scale multilaboratory evaluation indicated that the multiplex-competitive ELISA has good analytical reproducibility (average interlaboratory % CV of 28-41%).

Distinction of Signals Generated by Allergens from Cross-Reactivity in Botanicals Used in Dietary Supplements and Spices Using the xMAP Food Allergen Detection Assay

The xMAP Food Allergen Detection Assay (xMAP FADA) is a powerful analytical method by virtue of its ability to simultaneously detect multiple antigenic elements with a repertoire of antibodies targeting 15 food allergens plus gluten. Further, by incorporating multiple levels of redundancy, it can also be used to distinguish between homologous cross-reactive analytes. The power of its analytical capabilities is especially critical when working with botanicals. In this research, 95 botanicals used in dietary supplements and spices were analyzed for cross-reactivity with common food allergens and gluten using the xMAP FADA. Complementary antibody ratios were calculated, and, with most samples, ratios generated by homologous cross-reactive epitopes were easily distinguished from true reactivity. In very few cases, sample ratios were comparable to the ratios generated by the calibration standards, indicating the probable detection of relatively minor quantities of target food allergen. With the xMAP FADA, distinguishing signal indicating target allergen detection from cross-reactivity in botanicals is possible using redundant antibodies and multiple confirmatory end points.

Robustness Testing of the xMAP Food Allergen Detection Assay: A Multiplex Assay for the Simultaneous Detection of Food Allergens

ABSTRACT

The xMAP food allergen detection assay (xMAP FADA) can simultaneously detect 15 analytes (14 food allergens plus gluten) in one analysis. The xMAP FADA typically employs two antibody bead sets per analyte, providing built-in confirmation that is not available with other antibody-based assays. Before an analytical method can be used, its reliability must be assessed when conditions of the assay procedure are altered. This study was conducted to determine the effects on assay performance associated with changes in incubation temperature, amounts of the antibody bead cocktail, and concentrations of detection antibody and β-mercaptoethanol in the reduced-denatured extraction buffer. The analysis of buffered-detergent extracts revealed lower responses at 22°C than at 37°C, but temperature had no effect on the analysis of reduced-denatured extracts. Changes in β-mercaptoethanol and detection antibody concentrations had an effect on the detection of only milk in the reduced-denatured extracts. A slight change in the measured bead count was observed when one-fourth of the bead cocktail was used, and a large decrease in the bead count was noted when one-eighth of the recommended amount was used, but this number (≥25) was still sufficient to provide reliable results. Overall, the xMAP FADA was very robust to changes in the assay procedure, which may inadvertently occur.

HIGHLIGHTS

Extension of xMAP Food Allergen Detection Assay To Include Sesame

An estimated 0.1 to 0.2% of the North American population is allergic to sesame, and deaths due to anaphylactic shock have been reported. Detecting and quantifying sesame in various food samples is critical to safeguard the allergic population by ensuring accurate ingredient labeling. Because of the modular nature of the xMAP Food Allergen Detection Assay (FADA), it was possible through method extension to add sesame as a validated additional analyte. Because raw and toasted sesame are both commonly used and the two display significantly different antigenicity, three antibodies, one monoclonal and two polyclonal, were conjugated to bead sets to ensure reliable detection. The modified xMAP FADA successfully detected sesame incurred or spiked in baked muffins, spice mix, canola oil, and in both raw and toasted sesame oils with limit of quantitation values ≤ 1.3 ppm of sesame. Canola oil, sesame oil, toasted sesame oil, and olive oil inhibited sesame detection, as did the detection of sesame incurred in foods containing oil (e.g., hummus). Despite this inhibition, the xMAP FADA was still able to reliably detect sesame at levels throughout the dynamic range of the assay (22 to 750 ng of protein per mL) in all the foods examined. Further, the high signal-to-noise ratio of the lowest calibration standard and preliminary studies conjugating the antibodies at higher concentrations indicate an ability to increase the sensitivity of the assay should the need arise.

Detection of Ricin in Food Using Electrochemiluminescence-Based Technology

Ricin is a toxic ribosome inactivating protein (RIP-II) present in beans of the castor plant, Ricinus communis. Its potential as a biodefense threat has made the rapid, sensitive detection of ricin in food important to the U.S. Food and Drug Administration. Samples of juice, dairy products, soda, vegetables, bakery products, chocolate, and condiments were spiked with varying concentrations of ricin and analyzed using a 96-well format, electrochemiluminescence (ECL) immunoassay. Assay configurations included the use of a monoclonal capture antibody coupled with either a polyclonal or monoclonal detector antibody. The samples and detector antibodies were either added sequentially or in combination during the capture step. Using the polyclonal antibody, 0.04 ng/mL ricin was detected in analytical samples prepared from several beverages. By simultaneously incubating the sample with detector antibody, it was possible to decrease the assay time to a single 20 min incubation step with a limit of detection <10 ng/mL. Assays run according to this single incubation step exhibited a hook effect (decrease in signal at high concentrations of ricin), but because of the large signal-to-noise ratio associated with the ECL assay, the response remained above background and detectable. Thus, the ECL assay was uniquely suited for the screening of samples for ricin.

Detection and Quantitation of Gluten in Fermented-Hydrolyzed Foods by Antibody-Based Methods: Challenges, Progress, and a Potential Path Forward

Celiac disease (CD) affects ~1 in 141 individuals in the United States, requiring adherence to a strict gluten-free diet. The Codex Standard and the European Commission states that gluten level of gluten-free foods must not exceed 20 ppm. The FDA requires food bearing the labeling claim “gluten-free” to contain <20 ppm gluten. Accurate quantitation of gluten in fermented-hydrolyzed foods by antibody-based methods is a challenge due to the lack of appropriate reference materials and variable proteolysis. The recent uses of proteases (e.g., proline endopeptidases or PEP) to hydrolyze immunopathogenic sequences of gluten proteins further complicates the quantitation of immunopathogenic gluten. The commercially available antibody-based methods routinely used to detect and quantitate gluten are not able to distinguish between different hydrolytic patterns arising from differences in fermentation processes. This is a severe limitation that makes accurate quantitation and, ultimately, a detailed evaluation of any potential health risk associated with consuming the food difficult. Utilizing gluten-specific antibodies, a recently developed multiplex-competitive ELISA along with western blot analysis provides a potential path forward in this direction. These complimentary antibody-based technologies provide insight into the extent of proteolysis resulting from various fermentation processes and have the potential to aid in the selection of appropriate hydrolytic calibration standards, leading to accurate gluten quantitation in fermented-hydrolyzed foods.

Single-Laboratory Validation of the Multiplex xMAP Food Allergen Detection Assay with Incurred Food Samples

An xMAP Food Allergen Detection Assay (xMAP FADA) was developed to meet analytical needs when responding to complaints by individuals with multiple food allergies and to address potential ambiguities associated with cross-reactive proteins. A single-laboratory validation (SLV) was conducted to examine the reliability of the xMAP FADA to detect 15 analytes individually or as part of a mixture at more than six concentrations in four foods. The xMAP FADA reliably detected the analytes despite the incurred dark chocolate and incurred baked muffins displaying recoveries of 10-20% and <60%, respectively. The high reliability for recoveries less than 60% in part reflects the statistical strength of the design of the xMAP FADA. Only crustacean, egg, and milk incurred in dark chocolate were not reliably detected using the PBST-buffered-detergent protocol. Following the reduced-denatured protocol, no problems were encountered in the detection of milk, although egg did not display a dynamic response in dark chocolate. The ruggedness of the xMAP FADA was ascertained by the ability of novice analysts to detect food allergens in baked rice cookies. Despite one analyst losing >80% of the beads and the count for one bead set dropping to seven, the assay displayed only a decrease in precision (increased standard deviations) and a change in the ratios between complementary antibody pairs.

Application of Multiantigen Profiling To Detect Pecan

A problem often encountered in the detection and identification of undeclared tree nut food allergens is the lack of analytical methods. This problem is accentuated by the current trend, whereby the primary methods used to detect food allergens are antibody-based enzyme-linked immunosorbent assays (ELISAs) and the development of analyte-specific antibodies takes months. The recently developed xMAP food allergen detection assay (xMAP FADA) has the ability to generate multiantigen profiles with tree nuts, thereby providing a potential solution to this problem. The xMAP FADA includes 22 antibodies targeting peanut, soy, and nine tree nuts. The high number of antibodies to a diverse group of tree nuts and legumes and the propensity of tree nuts to cross-react have enabled the development of multiantigen profiling, whereby an analyte reacts with the various antibodies to generate a profile. Recently, a question arose regarding the possible presence of pecan dust at a manufacturer of pecan products that also stored fresh produce. The lack of suitable pecan ELISAs created an analytical challenge that was resolved using multiantigen profiling with the xMAP FADA. Pecan was detected on swab samples by using multiantigen profiling and confirmed by DNA analysis. The use of multiantigen profiling provided an analytical capability beyond what was possible with an analyte-specific analytical method.

A multiplex competitive ELISA for the detection and characterization of gluten in fermented-hydrolyzed foods

A novel competitive ELISA was developed utilizing the G12, R5, 2D4, MIoBS, and Skerritt antibody-HRP conjugates employed in nine commercial ELISA test kits that are routinely used for gluten detection. This novel multiplex competitive ELISA simultaneously measures gliadin-, deamidated gliadin-, and glutenin-specific epitopes. The assay was used to evaluate 20 wheat beers, 20 barley beers, 6 barley beers processed to reduce gluten, 15 soy sauces, 6 teriyaki sauces, 6 Worcestershire sauces, 6 vinegars, and 8 sourdough breads. For wheat beers, the apparent gluten concentration values obtained by the G12 and Skerritt antibodies were typically higher than those obtained using the R5 antibodies. The sourdough bread samples resulted in higher apparent gluten concentration values with the Skerritt antibody, while the values generated by the G12 and R5 antibodies were comparable. Although the soy-based sauces showed non-specific inhibition with the multiple R5 and G12 antibodies, their overall profile was distinguishable from the other categories of fermented foods. Cluster analysis of the apparent gluten concentration values obtained by the multiplex competitive ELISA, as well as the relative response of the nine gluten-specific antibodies used in the assay to different gluten proteins/peptides, distinguishes among the different categories of fermented-hydrolyzed foods by recognizing the differences in the protein/peptide profiles characteristic of each product. This novel gluten-based multiplex competitive ELISA provides insight into the extent of proteolysis resulting from various fermentation processes, which is essential for accurate gluten quantification in fermented-hydrolyzed foods. Graphical abstract A novel multiplex competitive ELISA for the detection and characterization of gluten in fermented-hydrolyzed foods.

Cross-reactivity profiles of legumes and tree nuts using the xMAP® multiplex food allergen detection assay

The homology between proteins in legumes and tree nuts makes it common for individuals with food allergies to be allergic to multiple legumes and tree nuts. This propensity for allergenic and antigenic cross-reactivity means that commonly employed commercial immunodiagnostic assays (e.g., dipsticks) for the detection of food allergens may not always accurately detect, identify, and quantitate legumes and tree nuts unless additional orthogonal analytical methods or secondary measures of analysis are employed. The xMAP^® Multiplex Food Allergen Detection Assay (FADA) was used to determine the cross-reactivity patterns and the utility of multi-antibody antigenic profiling to distinguish between legumes and tree nuts. Pure legumes and tree nuts extracted using buffered detergent displayed a high level of cross-reactivity that decreased upon dilution or by using a buffer (UD buffer) designed to increase the stringency of binding conditions and reduce the occurrence of false positives due to plant-derived lectins. Testing for unexpected food allergens or the screening for multiple food allergens often involves not knowing the identity of the allergen present, its concentration, or the degree of modification during processing. As such, the analytical response measured may represent multiple antigens of varying antigenicity (cross-reactivity). This problem of multiple potential analytes is usually unresolved and the focus becomes the primary analyte, the antigen the antibody was raised against, or quantitative interpretation of the content of the analytical sample problematic. The alternative solution offered here to this problem is the use of an antigenic profile as generated by the xMAP FADA using multiple antibodies (bead sets). By comparing the antigenic profile to standards, the allergen may be identified along with an estimate of the concentration present. Cluster analysis of the xMAP FADA data was also performed and agreed with the known phylogeny of the legumes and tree nuts being analyzed. Graphical abstract The use of cluster analysis to compare the multi-antigen profiles of food allergens.

Detection and Antigenic Profiling of Undeclared Peanut in Imported Garlic Using an xMAP Multiplex Immunoassay for Food Allergens

A shipment of imported garlic powder was suspected of containing peanut. Samples (subs) collected from the shipment displayed considerable variability in peanut antigenicity when analyzed by enzyme-linked immunosorbent assay (ELISA). This raised questions regarding whether peanut was actually present, the amount present, and the basis for the variability in antigenic content. Analyses that used an xMAP multiplex assay for the detection of peanut and additional food allergens generated responses that were characteristic of peanut. Specifically, the relative intensities of two different peanut-specific antibodies coupled to beads (peanut-37 and -38) and the antigen profiles were identical to garlic controls spiked with peanut. In addition, the xMAP data did not indicate the presence of other allergens. Quantitative analyses indicated an approximately fivefold variation in peanut concentration among different subs. In contrast, within a sub, the apparent peanut concentration appeared constant. Particle size analyses of the garlic powder subs indicated a single distribution profile, with a peak at 380 μm. ELISA analysis of sieve-fractionated garlic powder from one of the subs indicated that slightly less than half of the detectable peanut was smaller than 212 μm, with the remainder almost evenly split between 212 and 300 μm and >300 μm. Modeling to predict possible oral exposure levels of peanut other than those directly measured requires additional research on the physicochemical properties of peanut and garlic, along with information on the production of the garlic powder.

Detection of Gluten during the Fermentation Process To Produce Soy Sauce

Advances have been made to provide people with celiac disease (CD) access to a diverse diet through an increase in the availability of gluten-free food products and regulations designed to increase label reliability. Despite advances in our knowledge regarding CD and analytical methods to detect gluten, little is known about the effects of fermentation on gluten detection. The enzyme-linked immunosorbent assay (ELISA) and lateral flow devices routinely used by analytical laboratories and regulatory agencies to test for the presence of gluten in food were examined for their ability to detect gluten during the fermentation processes leading to the production of soy sauce, as well as in finished products. Similar results were observed irrespective of whether the soy sauce was produced using pilot-plant facilities or according to a homemade protocol. In both cases, gluten was not detected after moromi (brine-based) fermentation, which is the second stage of fermentation. The inability to detect gluten after moromi fermentation was irrespective of whether the assay used a sandwich configuration that required two epitopes or a competitive configuration that required only one epitope. Consistent with these results was the observation that ELISA, lateral flow devices, and Western immunoblot analyses were unable to detect gluten in commercial soy sauce, teriyaki sauce, and Worcestershire sauce. Although reports are lacking on problems associated with the consumption of fermented soy-containing sauces by consumers with CD, additional research is needed to determine whether all immunopathogenic elements in gluten are hydrolyzed during soy sauce production.

A Limited Survey of Dark Chocolate Bars Obtained in the United States for Undeclared Milk and Peanut Allergens

Undeclared allergens in chocolate products have been responsible for numerous allergen-related recalls in the United States. A survey was conducted to determine the prevalence of undeclared milk and peanut in 88 and 78 dark chocolate bars, respectively. Concentrations of milk (as nonfat dry milk) or peanut in three samples of each chocolate product were determined with two milk- or peanut-specific enzyme-linked immunosorbent assay kits. In 75% of the chocolate bar products with a milk advisory statement, milk concentrations were above the limit of quantitation (2.5 μg/g [ppm]), with the majority having concentrations >1,000 ppm. An additional 67% of chocolate bars with a "traces of milk" statement contained 3 to 6,700 ppm of milk. Fifteen percent of chocolates labeled dairy free or lactose free and 25% labeled vegan were positive for milk, all with concentrations >1,000 ppm. Even for chocolates with no reference to milk on the label, 33% of these products contained 60 to 3,400 ppm of milk. The survey of chocolate products for peanuts revealed that 8% of products with an advisory statement contained peanut, with the highest concentration of 550 ppm. All nine chocolates bearing the peanut-free or allergen-free statement were negative for peanut, but 17% of chocolates with no label statement for peanut were positive for peanut at concentrations of 9 to 170 ppm. Evaluation of multiple lots of four chocolate products revealed that milk was consistently present or absent for the products investigated, but mixed results were obtained when multiple lots were tested for peanut. This study indicates that a large proportion of dark chocolate bars contain undeclared milk. The type of advisory statement or the absence of a milk advisory statement on products did not predict the amount or absence of milk protein. In contrast, a lower proportion of chocolates containing undeclared peanut was found. Consumers with food allergies should be cautious when purchasing dark chocolate products, particularly those that have an advisory label statement.

Presence of Undeclared Food Allergens in Cumin: The Need for Multiplex Methods

Beginning in the autumn of 2014, millions of dollars of food and over 675 products were recalled in the United States due to the presence of undeclared peanut, attributed to cumin used in the manufacture of the products. Initial analyses also indicated the presence of almond. Subsequent research showed that the presence of peanut and almond did not fully explain the analytical results for the cumin samples. Using a combination of mass spectrometry, DNA-based methods (i.e., PCR and Sanger DNA Sequencing), microscopy, and antibody-based technologies (i.e., ELISA, Western blot analysis, and a novel xMAP multiplex assay) the presence of peanut was confirmed. Screening for secondary sources of adulteration (e.g., tree nuts, mahleb, peach, and cherry) supported the assessment that the cumin contained multiple contaminants. These results demonstrate the limitations of single analyte-specific assays and the need for orthogonal multiplex methods to detect food allergens irrespective of varietal or other differences.

Effects of a Proline Endopeptidase on the Detection and Quantitation of Gluten by Antibody-Based Methods during the Fermentation of a Model Sorghum Beer

The effectiveness of a proline endopeptidase (PEP) in hydrolyzing gluten and its putative immunopathogenic sequences was examined using antibody-based methods and mass spectrometry (MS). Based on the results of the antibody-based methods, fermentation of wheat gluten containing sorghum beer resulted in a reduction in the detectable gluten concentration. The addition of PEP further reduced the gluten concentration. Only one sandwich ELISA was able to detect the apparent low levels of gluten present in the beers. A competitive ELISA using a pepsin-trypsin hydrolysate calibrant was unreliable because the peptide profiles of the beers were inconsistent with that of the hydrolysate calibrant. Analysis by MS indicated that PEP enhanced the loss of a fragment of an immunopathogenic 33-mer peptide in the beer. However, Western blot results indicated partial resistance of the high molecular weight (HMW) glutenins to the action of PEP, questioning the ability of PEP in digesting all immunopathogenic sequences present in gluten.

Detection and Quantification of Gluten during the Brewing and Fermentation of Beer Using Antibody-Based Technologies

In 2013 the U.S. Food and Drug Administration (FDA) defined the term ''gluten-free'' and identified a gap in the analytical methodology for detection and quantification of gluten in foods subjected to fermentation and hydrolysis. To ascertain the ability of current enzyme-linked immunosorbent assays (ELISAs) to detect and quantify gluten in fermented and hydrolyzed products, sorghum beer was spiked in the initial phases of production with 0, 20, and 200 μg/ml wheat gluten, and samples were collected throughout the beer production process. The samples were analyzed using five sandwich ELISAs and two competitive ELISAs and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with Western analysis employing four antibodies (MIoBS, R5, G12, and Skerritt). The sensitivity of the MIoBS ELISA (0.25 ppm) enabled the reliable detection of gluten throughout the manufacturing process, including fermentation, when the initial concentration of 20 μg/ml dropped to 2 μg/ml. The R5 antibody-based and G12 antibody-based sandwich ELISAs were unable to reliably detect gluten, initially at 20 μg/ml, after the onset of production. The Skerritt antibody-based sandwich ELISA overestimated the gluten concentration in all samples. The R5 antibody-based and G12 antibody-based competitive ELISAs were less sensitive than the sandwich ELISAs and did not provide accurate results for quantifying gluten concentration. The Western analyses were able to detect gluten at less than 5 μg/ml in the samples and confirmed the results of the ELISAs. Although further research is necessary before all problems associated with detection and quantification of hydrolyzed and fermented gluten are resolved, the analytical methods recommended by the FDA for regulatory samples can detect ≥ 20 μg/ml gluten that has undergone brewing and fermentation processes associated with the manufacture of beer.

Survey of tea for the presence of gluten

In 2013, the U.S. Food and Drug Administration conducted a survey of green and white teas marketed in the northeastern United States for the presence of undeclared wheat. Based on the requirement for concurrence between the RIDASCREEN gliadin (R5) enzyme-linked immunosorbent assay (ELISA) and the Morinaga Institutes of Biological Science (MIoBS) wheat protein ELISA, none of the 20 products included in the survey tested positive for wheat, rye, barley, or gluten. However, eight of the teas generated responses indicative of the presence of gluten with the RIDASCREEN gliadin (R5), AgraQuant gluten G12, and Aller-Tek (Skerritt) sandwich ELISAs. Five of the eight teas generated responses indicative of >20 ppm of gluten using the RIDASCREEN and AgraQuant ELISA test kits, and all eight had ≥ 20 ppm based on the Aller-Tek ELISA. Extracts prepared using the RIDASCREEN validated protocol and the MIoBS validated sodium dodecyl sulfate plus β-mercaptoethanol (overnight) protocol were analyzed using both test kits. The extracts prepared using the RIDASCREEN protocol tested positive for gluten with both test kits. Western blot analyses of the two sets of extracts using the R5 and MIoBS antibodies to visualize the bands revealed the presence of antigenic proteins in both sets of extracts, although the profiles and band intensities were different and inconsistent with the ELISA results. These results raise questions regarding the screening procedures used to detect gluten and how the observation of a homologous antigenic element is defined.

Multiplex detection of food allergens and gluten

To help safeguard the food supply and detect the presence of undeclared food allergens and gluten, most producers and regulatory agencies rely on commercial test kits. Most of these are ELISAs with a few being PCR-based. These methods are very sensitive and analyte specific, requiring different assays to detect each of the different food allergens. Mass spectrometry offers an alternative approach whereby multiple allergens may be detected simultaneously. However, mass spectrometry requires expensive equipment, highly trained analysts, and several years before a quantitative approach can be achieved. Using multianalyte profiling (xMAP®) technology, a commercial multiplex test kit based on the use of established antibodies was developed for the simultaneous detection of up to 14 different food allergens plus gluten. The assay simultaneously detects crustacean seafood, egg, gluten, milk, peanut, soy, and nine tree nuts (almond, Brazil nut, cashew, coconut, hazelnut, macadamia, pine nut, pistachio, and walnut). By simultaneously performing multiple tests (typically two) for each analyte, this magnetic bead-based assay offers built-in confirmatory analyses without the need for additional resources. Twenty-five of the assays were performed on buffer extracted samples, while five were conducted on samples extracted using reduced-denatured conditions. Thus, complete analysis for all 14 allergens and gluten requires only two wells of a 96-well microtiter plate. This makes it possible to include in a single analytical run up to 48 samples. All 30 bead sets in this multiplex assay detected 5 ng/mL of food allergen and gluten with responses greater than background. In addition, 26 of the bead sets displayed signal/noise ratios of five or greater. The bead-based design makes this 30-plex assay expandable to incorporate new antibodies and capture/detector methodologies by ascribing these new detectors to any of the unassigned bead sets that are commercially available.

Simultaneous multiplex detection and confirmation of the proteinaceous toxins abrin, ricin, botulinum toxins, and Staphylococcus enterotoxins a, B, and C in food

Detection of proteinaceous toxins in complex heterogeneous mixtures requires highly specific and sensitive methods. Multiplex technology employing multiple antibodies that recognize different epitopes on a toxin provides built-in confirmatory analysis as part of the initial screen and thereby increases the reliability associated with both presumptive positive and negative results. Polyclonal and monoclonal antibodies were obtained for abrin, botulinum toxins, ricin, and Staphylococcus enterotoxins A, B, and C (SEA, SEB, and SEC). Food samples were spiked with the toxins either individually or mixed and analyzed following 40-fold dilution. Abrin, botulinum toxin A complex, ricin, and SEB displayed limits of detection in the original food samples ranging from 0.03 to 1.3 microg/mL, from 0.03 to 0.07 microg/mL, from 0.01 to 0.1 microg/mL, and from <0.01 to 0.03 microg/mL, respectively. Redundancy, that is, multiple antibodies for each toxin, some recognizing different epitopes or displaying different binding affinities, provided a "fingerprint" for the presence of the toxins and built-in confirmation, thus reducing the likelihood of false-positive and false-negative results. Inclusion of internal controls, including a unique protein, helped control for variations in dilution. Paramagnetic microspheres facilitated the detection of analyte in foods containing particulate matter incompatible with the use of filter plates normally used in the wash steps of assays employing standard polystyrene microspheres.

Application of deadenylase electrochemiluminescence assay for ricin to foods in a plate format

A recently developed bead-based deadenylase electrochemiluminescence assay for ricin is simple and sensitive in its ability to detect ricin, based on the catalytic activity of the toxin subunit, ricin A chain. The assay was modified to work in a 96-well plate format and evaluated by using juice samples. The plate-based assay, unlike the bead-based assay, includes wash steps that enable the removal of food particles. These steps minimize matrix effects and improve the signal-to-noise ratios and limits of detection (LOD). The LOD values for ricin in apple juice, vegetable juice, and citrate buffer by using the bead-based assay were 0.4, 1, and 0.1 microg/ml, respectively. In contrast, the LOD values for ricin by using the plate-based assay were 0.04, 0.1, and 0.04 microg/ml in apple juice, vegetable juice, and citrate buffer, respectively. The plate-based assay displayed three- to 10-fold lower LOD values than did the bead-based assay. Signal-to-noise ratios for the plate-based assay were comparable to those for the bead-based assay for ricin in citrate buffer, but 2- to 4.5-fold higher when the plate-based assay was used for analysis of juice samples.

Toxicity and detection of ricin and abrin in beverages

The oral and intraperitoneal (i.p.) toxicities to female BALB/c mice of ricin and abrin in phosphate-buffered saline (PBS), spring water, apple juice, and half-and-half (only oral) were examined after brief (2 h) and prolonged (11 to 13 days) storage. The ricin and abrin samples prepared in PBS had oral toxicities consistent with those previous studies, indicating oral and i.p. 50% lethal doses of > 1 mg/kg of body weight and between 2 and 20 microg/kg of body weight, respectively. The toxicities of ricin and abrin in PBS were greater than those in apple juice and water. The oral toxicity of ricin and abrin in half-and-half appeared comparable to or less than that observed for the toxins in water. Spiked samples stored for a maximum of 11 days (13 for the abrin samples) at 4 degrees C induced similar numbers of fatalities as did samples stored for only 2 h. Enzyme-linked immunosorbent assays of the samples administered by i.p. injection indicated a decrease in detectable toxin at 0.5 microg/ml.

Detection of abrin in food using enzyme-linked immunosorbent assay and electrochemiluminescence technologies

Abrin is a toxic ribosome-inactivating protein present in beans of Abrus precatorius, also known as rosary peas. The possibility that abrin could be used to adulterate food has made the development of assays for the detection of abrin a priority. Rabbit-derived polyclonal antibodies and mouse monoclonal antibodies were prepared against a mixture of abrin isozymes. The specificity and cross-reactivity of the antibodies were evaluated against a challenge library of 40 grains, nuts, legumes, and foods. An enzyme-linked immunosorbent assay (ELISA) and an electrochemiluminescence (ECL)-based assay were assembled and optimized. Polyclonal (capture) and polyclonal (detection) ELISAs, polyclonal and monoclonal ELISAs, and polyclonal and monoclonal ECL assays had limits of detection (LODs) of 0.1 to 0.5 ng/ml for abrin in buffer. The LOD for abrin dissolved into juices, dairy products, soda, chocolate drink, and condiments and analyzed with the ECL assay ranged from 0.1 to 0.5 ng/ml in the analytical sample. In contrast, the LODs for the ELISAs ranged from 0.5 to 10 ng/ml in the analytical sample.

Identification of the RNA N-glycosidase activity of ricin in castor bean extracts by an electrochemiluminescence-based assay

A simple electrochemiluminescence-based assay for RNA N-glycosidase activity has been modified to permit its use with authentic extracts of Ricinus communis (castor beans) and Abrus precatorius (jequirity seeds)--the natural sources of ricin and abrin. Modifications include the addition of an RNase inactivator to the reaction mixture, elimination of a signal-enhancing monoclonal antibody, and optimization of the incubation temperature. Concurrent testing with two substrates provides a diagnostic tool enabling castor bean toxins to be differentiated from a larger selection of N-glycosidase toxins than was previously examined.

Detection of ricin in food using electrochemiluminescence-based technology

Ricin is a toxic ribosome inactivating protein (RIP-II) present in beans of the castor plant, Ricinus communis. Its potential as a biodefense threat has made the rapid, sensitive detection of ricin in food important to the U.S. Food and Drug Administration. Samples of juice, dairy products, soda, vegetables, bakery products, chocolate, and condiments were spiked with varying concentrations of ricin and analyzed using a 96-well format, electrochemiluminescence (ECL) immunoassay. Assay configurations included the use of a monoclonal capture antibody coupled with either a polyclonal or monoclonal detector antibody. The samples and detector antibodies were either added sequentially or in combination during the capture step. Using the polyclonal antibody, 0.04 ng/mL ricin was detected in analytical samples prepared from several beverages. By simultaneously incubating the sample with detector antibody, it was possible to decrease the assay time to a single 20 min incubation step with a limit of detection <10 ng/mL. Assays run according to this single incubation step exhibited a hook effect (decrease in signal at high concentrations of ricin), but because of the large signal-to-noise ratio associated with the ECL assay, the response remained above background and detectable. Thus, the ECL assay was uniquely suited for the screening of samples for ricin.

Detection of melamine using commercial enzyme-linked immunosorbent assay technology

Recent cases of adulteration with melamine have led to the need for rapid and reliable screening methods. To meet this need, commercial enzyme-linked immunosorbent assay (ELISA) test kits for the detection of triazines were evaluated. The recently released Melamine Plate kit (Abraxis, Warminster, Pa.) displayed a limit of detection of 9 ng/ml for melamine in phosphate-buffered saline (PBS) and approximately 1 microg/ml for melamine added to dog food. An atrazine ELISA test kit produced by Abraxis required 0.2 mg/ml to generate a response more than four times the standard deviation from background. In contrast, with the EnviroGard Triazine Plate kit (Strategic Diagnostics, Inc., Newark, Del.), 1.5 mg/ml melamine in PBS generated a signal only one standard deviation from background, which was insufficient to define a limit of detection. Extraction based on dilution with 105 mM sodium phosphate/75 mM NaCl/2.5% nonfat milk/0.05% Tween 20 (UD) enabled detection of fivefold less melamine in dog food than did use of the procedure recommended by the manufacturer, which entailed extraction into 60% methanol, sonication, centrifugation, filtration, and further dilution into 10% methanol/PBS. Using the Abraxis Melamine ELISA, both extraction protocols yielded identical results with a dog food sample adulterated with melamine. The recovery of melamine spiked into gravy from dog food using UD was 74% +/- 4%. In conclusion, the recently released Abraxis ELISA for melamine proved to be a useful alternative to more cumbersome methods.

Feasibility of immunodiagnostic devices for the detection of ricin, amanitin, and T-2 toxin in food

Qualitative and quantitative comparisons were conducted of commercially available immunodiagnostic devices for the detection of three select agents with oral LD50 values > or = 0.1 mg/kg of body weight. Ricin (oral LD50 > 1 mg/kg), amanitin (oral LD50 approximately 0.1 mg/kg), and T-2 toxin (oral LD50 > 1 mg/kg) were spiked into beverages, produce, dairy, and baked goods and assayed using commercially available enzyme-linked immunosorbent assays (ELISAs) and lateral flow devices. In all cases, the commercial diagnostic kits successfully detected all three select agents at concentrations below what might be a health concern. The considerable difference between the limit of detection of the immunodiagnostic devices employed (typically < or = 0.020 microg/g) and the amount of the select agent necessary to pose a health threat in a single serving of food facilitated the design of protocols for the high throughput screening of food samples. These protocols entailed simple extraction methods followed by sample dilution. Lateral flow devices and sandwich ELISAs for the detection of ricin had no significant background problems due to the food matrices. Competitive ELISAs, which typically have unacceptably high background reactions with food samples, successfully detected amanitin and T-2 toxin.

Performance Tested Method multiple laboratory validation study of ELISA-based assays for the detection of peanuts in food

Performance Tested Method multiple laboratory validations for the detection of peanut protein in 4 different food matrixes were conducted under the auspices of the AOAC Research Institute. In this blind study, 3 commercially available ELISA test kits were validated: Neogen Veratox for Peanut, R-Biopharm RIDASCREEN FAST Peanut, and Tepnel BioKits for Peanut Assay. The food matrixes used were breakfast cereal, cookies, ice cream, and milk chocolate spiked at 0 and 5 ppm peanut. Analyses of the samples were conducted by laboratories representing industry and international and U.S governmental agencies. All 3 commercial test kits successfully identified spiked and peanut-free samples. The validation study required 60 analyses on test samples at the target level 5 microg peanut/g food and 60 analyses at a peanut-free level, which was designed to ensure that the lower 95% confidence limit for the sensitivity and specificity would not be <90%. The probability that a test sample contains an allergen given a prevalence rate of 5% and a positive test result using a single test kit analysis with 95% sensitivity and 95% specificity, which was demonstrated for these test kits, would be 50%. When 2 test kits are run simultaneously on all samples, the probability becomes 95%. It is therefore recommended that all field samples be analyzed with at least 2 of the validated kits.

Low levels of sodium and potassium in the water from wetlands in Minnesota that contained malformed frogs affect the rate of Xenopus development

Water samples were collected between 1999 and 2000 from wetlands in Minnesota that contained malformed frogs. The water samples were analyzed for 14 minerals/ions and screened for the presence of biologically active compounds using Xenopus laevis. Results indicated that water from two sites, CWB and ROI2, induced severe retardation with embryo lengths reduced 20% after 96 hr of development. The developmental delay observed with water from ROI2 was alleviated by supplementation with sodium, while both sodium and potassium alleviated the developmental delay observed with water whose mineral content mimicked that of CWB. Seasonal fluctuations in the sodium and potassium content at ROI2 and NEY correlated with changes in the rates of Xenopus development. Xenopus embryos reared on water from ROI2 for 120 hr displayed gut malformations not present in embryos reared on a synthetic media designed to mimic the mineral content of the water from ROI2. Embryos reared on water from ROI2 supplemented with minerals at levels comparable to that routinely employed in the rearing of Xenopus were neither retarded nor malformed. It is proposed that climate driven hydrology may influence the mineral composition at selected wetlands and delay development which may alter window(s) of susceptibility towards biologically active agents and the occurrence of malformed frogs.

Mineral deficiency and the use of the FETAX bioassay to study environmental teratogens

The Frog Embryo Teratogenesis Assay: Xenopus (FETAX) bioassay has been employed extensively to screen compounds for teratogenic activity. Recent laboratory studies have indicated that low potassium concentrations retard Xenopus laevis development. The effects of varying concentrations of minerals on Xenopus laevis embryo length and development were examined to determine the utility of the FETAX bioassay in the study of environmental teratogens. Water samples collected from 18 wetlands in Minnesota and North Dakota correlated with low mineral levels, causing delayed embryonic development in the FETAX bioassay. When the concentration of sodium or potassium was <5 ppm, Xenopus laevis development was delayed. As a result, it was difficult to assess teratogenic activity after 96 h of incubation. Furthermore, the length of the embryos-an indication of development-paralleled changes in mineral composition. Comparisons between different wetlands based on changes in one specific mineral were not possible due to a synergism between various minerals. If the concentration of sodium and/or potassium was <5 ppm but > or =2 ppm, extension of the FETAX bioassay to 120 h allowed organogenesis to proceed through stage 46, as required for scoring in accordance with ASTM guidelines for the FETAX bioassay. In those cases in which the concentration of sodium and/or potassium were <2 ppm, the embryos could not develop to stage 46 within 120 h and the FETAX bioassay was not suitable for detecting teratogenic activity. Published in 2002 by John Wiley & Sons, Ltd.