Monoclonal-Antibody-Based Immunoassays for the Mycotoxins NX-2 and NX-3 in Wheat

The fungal infestation of crops can cause major economic losses. Toxins produced by the causative fungi (mycotoxins) represent a potential safety hazard to people and livestock consuming them. One such mycotoxin is deoxynivalenol (DON, also known as vomitoxin), a trichothecene associated with Fusarium Head Blight of wheat. DON is commonly found in cereal crops worldwide. A group of trichothecene mycotoxins closely related to DON, the NX toxins, have been reported to occur in the northeastern United States and southern Canada. While many commercial immunoassays are available to detect DON, there are no rapid screening assays for the NX toxins. We describe the development and isolation of three monoclonal antibodies (mAbs) specific towards two NX toxins: NX-2 and NX-3. The mAbs did not recognize DON or several other closely related trichothecenes. One of the mAbs was selected for development of an enzyme-linked immunosorbent assay (ELISA) for NX-2 and NX-3 in wheat. The dynamic ranges for the assay were 7.7 to 127 μg/kg for NX-2 and 59 μg/kg to 1540 μg/kg for NX-3 in wheat. Recoveries from spiked wheat averaged 84.4% for NX-2 and 99.3% for NX-3, with RSDs of 10.4% and 11.3%, respectively (n = 24). The results suggest that this assay can be used to screen for NX toxins in wheat at levels relevant to human food and animal feed safety.

Homogeneous immunoassay for cyclopiazonic acid based upon mimotopes and upconversion-resonance energy transfer

Strains of Penicillium spp. are used for fungi-ripened cheeses and Aspergillus spp. routinely contaminate maize and other crops. Some of these strains can produce toxic secondary metabolites (mycotoxins), including the neurotoxin α-cyclopiazonic acid (CPA). In this work, we developed a homogeneous upconversion-resonance energy transfer (UC-RET) immunoassay for the detection of CPA using a novel epitope mimicking peptide, or mimotope, selected by phage display. CPA-specific antibody was used to isolate mimotopes from a cyclic 7-mer peptide library in consecutive selection rounds. Enrichment of antibody binding phages was achieved, and the analysis of individual phage clones revealed four different mimotope peptide sequences. The mimotope sequence, ACNWWDLTLC, performed best in phage-based immunoassays, surface plasmon resonance binding analyses, and UC-RET-based immunoassays. To develop a homogeneous assay, upconversion nanoparticles (UCNP, type NaYF₄:Yb³⁺, Er³⁺) were used as energy donors and coated with streptavidin to anchor the synthetic biotinylated mimotope. Alexa Fluor 555, used as an energy acceptor, was conjugated to the anti-CPA antibody fragment. The homogeneous single-step immunoassay could detect CPA in just 5 min and enabled a limit of detection (LOD) of 30 pg mL^-1 (1.5 μg kg^-1) and an IC₅₀ value of 0.36 ng mL^-1. No significant cross-reactivity was observed with other co-produced mycotoxins. Finally, we applied the novel method for the detection of CPA in spiked maize samples using high-performance liquid chromatography coupled to a diode array detector (HPLC-DAD) as a reference method.

Cyclopiazonic acid in soft-ripened and blue cheeses marketed in the USA

Strains of Penicillium camemberti and P. roqueforti are used in the production of soft-ripened and blue-veined cheeses. However, some strains can produce toxic secondary metabolites (mycotoxins), including α-cyclopiazonic acid (CPA), a neurotoxin. Data on the levels of CPA in cheeses marketed in the USA are extremely limited. An enzyme-linked immunosorbent assay was adapted for measuring CPA in soft-ripened and blue-veined cheeses. Recoveries from cheese curds were 103 ± 27% (n = 30). A total of 254 samples of soft-ripened, blue and miscellaneous cheeses were examined. CPA was detected in 36/79 (45.6%) of soft-ripened cheeses and in 41/168 (24.4%) of blue-veined cheeses. Median levels in positive samples were 48.5 µg/kg and 30 µg/kg, respectively. The highest levels found were 3,820 µg/kg (in a Brie), 1,250 µg/kg (in a blue) and 7,900 µg/kg (in a Monte Enebro). The implication of such exposures is unknown, as a consensus on acceptable intake remains to be established.

Roquefortine C in blue-veined and soft-ripened Cheeses in the USA

Certain fungi can produce secondary metabolites that are toxic, mycotoxins. Two groups of cheeses where fungi are used for ripening are the blue-veined cheeses (Penicillium roqueforti) and the "soft-ripened" cheeses (P. camemberti). An enzyme-linked immunosorbent assay was used to screen for the mycotoxin roquefortine C (ROQC) in 202 samples of cheeses sold in the United States. Of these 152 were blue-veined cheeses, 46 were soft-ripened cheeses and 4 were other varieties of mould-ripened cheeses. ROQC was not detected in any of the soft-ripened cheeses, at a limit of detection of 1.8 µg/kg. ROQC was found in 151 of 152 blue-veined cheeses. The maximum level found was 6,630 µg/kg (median 903 µg/kg, average of positives 1430 µg/kg, limit of quantitation 6.9 µg/kg). These levels are consistent with the levels found previously in blue-veined cheeses in the United Kingdom and Europe, which have generally been considered non-hazardous for human consumption.

Development and characterisation of a monoclonal antibody to detect the mycotoxin roquefortine C

Roquefortine, also known as roquefortine C (ROQC) is a fungal secondary metabolite (mycotoxin) that is produced by some of the same Penicillia as the tremorgen penitrem-A (PEN-A). The two mycotoxins have been linked to sporadic cases of toxicosis in dogs, cattle, and humans, leading some to consider ROQC as a biomarker of PEN-A. Reported here are the development of a monoclonal antibody (mAb) and associated competitive enzyme-linked immunosorbent assay (ELISA) for the screening of ROQC in extracts of nuts (nut "milks"), and dog serum. The ELISA was sensitive for ROQC, with a level of 0.117 ng ml^-1 inhibiting colour development by 50% (IC₅₀), a limit of detection of 0.026 ng ml^-1, and a dynamic range (IC₂₀ to IC₈₀) of 0.038 to 0.289 ng ml^-1 in buffer. The assay was tolerant to significant levels of methanol. Recoveries from 4 types of nut milks spiked over the range of 0.25 to 2 ng ml^-1 were in the range of 83.5% to 116%. A small survey of commercial nut "milks" and "creamers" indicated 4 of 35 samples contained ROQC at levels so low that they are unlikely to be significant to human health (<0.6 ng ml^-1). The assay was also applied to canine serum. Recoveries from serum spiked over the range of 0.2 to 5 ng ml^-1 ranged from 98.1% to 123%. The results suggest the ELISA can be applied to the screening of food products, such as nut extracts, as well as for the screening of serum from dogs suspected to be suffering from mycotoxin-induced tremors.

Quantitation and Stability of Fumonisins B1 and B2 in Milk

The well-documented presence of fumonisin myco-toxins B1 and B2 (FB1 and FB2) in corn raises the possibility that these toxins are carried over into the milk of animals fed with contaminated feed. The presence of FB1 and FB2 in milk has not been assessed because of the lack of sensitive analytical techniques for this matrix. Two methods, liquid chromatography (LC) and enzyme-linked immunosorbent assay (ELISA), were adapted for the analysis of milk. The ELISA, produced commercially for screening corn, required no sample preparation and was reproducible but was of low sensitivity [concentration that inhibits color development by 50% (IC50), 1200-1600 ng FB1/mL]. The more sensitive LC method involves serial extraction of milk with methanol-acetone and strong anion exchange followed by derivatization with naphthalene-2,3-dicarboxaldehyde. Recoveries of 50 ng FB1 and FB2/mL from unpasteurized and un-homogenized milk were 84 and 83%, respectively (limit of detection, 5 ng/mL). Recoveries of FB1 from whole homogenized milk (76%) were slightly lower. Heating milk for 30 min at 62°C, to mimic pasteurization, did not significantly reduce FB1 or FB2 recovery, nor did storing milk for 11 days at 4°C. The LC method was applied to 165 samples of milk, only 1 of which was positive. This finding suggests that exposure of humans to FB1 and FB2 from milk is low.

Extraction of Aflatoxins B1 and G1 from Maize by Using Aqueous Sodium Dodecyl Sulfate

Aflatoxins are potent carcinogens produced by certain Aspergillus fungi. The aflatoxins were first discovered in the 1960s, and since then have been found to be distributed worldwide in a variety of commodities, foods, and feeds. Many of the early techniques for detecting aflatoxins involved extraction with halogenated solvents. With the increased availability and use of reversed-phase solid-phase extraction cartridges and the availability of immunoaffinity columns, aqueous mixtures of nonhalogenated solvents have been frequently used. To further reduce the need for solvents, we examined the effects of eliminating solvents during the extraction of maize, using aqueous mixtures of the detergent sodium dodecyl sulfate. After extraction and filtration, aflatoxins B1 (AFB1)and G1 (AFG1) were isolated by using commercially available immunoaffinity columns. The isolated AFB1 and AFG1 were derivatized with trifluoroacetic acid before separation by liquid chromatography with fluorescence detection. In spiked maize, the limits of detection were 0.5 and 1 ng/g for AFB1 and AFG1, respectively. Recoveries of AFB1 from maize spiked at 120 ng/g averaged 87.5 (range, 76.399.0), with an average repeatability relative standard deviation (RSDr) of 4.0. Recoveries of AFG1 from maize spiked at 220 ng/g averaged 80.4 (range, 70.385.8), with an average RSDr of 3.5. This is the first reported demonstration of an effective solvent-free extraction of aflatoxins from maize at ambient pressure, and this extraction procedure may serve to help reduce solvent consumption during aflatoxin analysis.

Determination of Deoxynivalenol and Nivalenol in Corn and Wheat by Liquid Chromatography with Electrospray Mass Spectrometry

The fungus Fusarium graminearum is a pathogen of both wheat and corn. Strains of the fungus from the United States produce a toxin, deoxynivalenol (DON); strains of the fungus from Asia and Europe produce DON or a related toxin, nivalenol. These toxins can cause disease in livestock, and their potential presence in feed and foods is a concern for animal and human health. A method was developed to detect both toxins in corn and wheat by liquid chromatography/mass spectrometry of an extract of ground grain. The method requires no sample cleanup and can detect the toxins at 0.05 μg/g.

Development and Characterization of Monoclonal Antibodies for the Mycotoxin Citreoviridin

Citreoviridin (CTV) in an inhibitor of mitochondrial ATPase that has been isolated from molded yellow rice and linked to the human disease Shoshin-kakke (acute cardiac beriberi). The disease results from a deficiency of thiamine, however, purified CTV can reproduce the symptoms in experimental animals. The link between CTV and Shoshin-kakke has been difficult to resolve, in part because cases of the disease are rare. In addition to rice, CTV has been found in maize, pecan nuts, and wheat products. A method to screen for CTV and its geometric isomer, iso-CTV, in commodities was developed, based upon the isolation of two novel monoclonal antibodies (mAb). In an antigen-immobilized competitive enzyme-linked immunosorbent assay format (CI-ELISA), the observed IC₅₀s for CTV were 11 ng/mL and 18 ng/mL (mAbs 2-2 and 2-4, respectively). The assays were relatively tolerant to methanol and acetonitrile, which allowed their application to the detection of CTV in spiked polished white rice. For quantification, a standard mixture of CTV and iso-CTV was used, along with matrix matched calibration. The dynamic range of the ELISA using mAb 2-4 was equivalent to 0.23 to 2.22 mg/kg in rice. Recoveries over the range of 0.36 to 7.23 mg/kg averaged 97 ± 10%. The results suggest that the mAb 2-4-based immunoassay can be applied to the screening of white rice for CTV. Both mAbs were also observed to significantly enhance the fluorescence of the toxin.

Fluorescence Polarization Immunoassay for the Determination of T-2 and HT-2 Toxins and Their Glucosides in Wheat

T-2 and HT-2 toxins and their main modified forms (T-2 glucoside and HT-2 glucoside) may co-occur in cereals and cereal-based products. A fluorescence polarization immunoassay (FPIA) was developed for the simultaneous determination of T-2 toxin, HT-2 toxin and relevant glucosides, expressed as sum. The developed FPIA, using a HT-2-specific antibody, showed high sensitivity (IC50 = 2.0 ng/mL) and high cross-reactivity (100% for T-2 toxin and 80% for T-2 and HT-2 glucosides). The FPIA has been used to develop two rapid and easy-to-use methods using two different extraction protocols, based on the use of organic (methanol/water, 90:10, v/v) and non-organic (water) solvents, for the determination of these toxins in wheat. The two proposed methods showed analytical performances in terms of sensitivity (LOD 10 µg/kg) recovery (92-97%) and precision (relative standard deviations ≤13%), fulfilling the criteria for acceptability of an analytical method for the quantitative determination of T-2 and HT-2 toxins established by the European Union. Furthermore, the methods were then validated in accordance with the harmonized guidelines for the validation of screening methods included in the Regulation (EU) No. 519/2014. The satisfactory analytical performances, in terms of intermediate precision (≤25%), cut-off level (80 and 96 µg/kg for the two methods) and rate of false positives (<0.1%) confirmed the applicability of the proposed methods as screening method for assessing the content of these toxins in wheat at the EU indicative levels reported for T-2 and HT-2 toxins.

Coordination of mycotoxins with lanthanides in luminescent complexes

The ability of several chelating mycotoxins to form coordination complexes with the lanthanide metals europium and terbium was explored. The mycotoxins examined included ochratoxin A, citrinin, cyclopiazonic acid (CPA), kojic acid, and tenuazonic acid (TeA). Of these compounds, TeA and CPA resulted in the greatest luminescence. Parameters influencing luminescence of TeA were investigated further. These included the type of lanthanide and its concentration, certain environmental factors, and the effect of competing metal cations. Of the two lanthanide metals, the terbium coordination complex (TeA-Tb³⁺) showed greater luminescence relative to the europium complex (TeA-Eu³⁺). The effects of solvent type, water content, and pH on the TeA-Tb³⁺ system suggested that optimal conditions for luminescence were in 90% methanol with 10% aqueous buffer at pH 3. In competitive assays, the luminescence of the TeA-Tb³⁺ complex decreased as the concentration of competing metal cations increased. Among the cations tested, Cu²⁺ was the best inhibitor followed by Al³⁺, Au³⁺, Fe³⁺, Co²⁺, Mn²⁺, Mg²⁺, and Ca²⁺. Two cations, Na⁺ and K⁺, showed no significant inhibition. This is the first report to describe the coordination of the metal-chelating mycotoxin TeA with lanthanides and the ability of TeA to serve as an "antenna" for the efficient transfer of energy to the lanthanide with resulting luminescence. Understanding the ability of mycotoxins such as TeA to chelate metals provides insight into how they exert their toxic effects.

Complexation of the Mycotoxin Cyclopiazonic Acid with Lanthanides Yields Luminescent Products

Cycopiazonic acid (CPA) is a neurotoxin that acts through inhibition of the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA). CPA blocks the calcium access channel of the enzyme. The inhibition may involve the binding of CPA with a divalent cation such as Mg2+. The potential for CPA to act as a chelator also has implications for methods to detect this toxin. Certain of the lanthanide metals undergo a dramatic increase in luminescence upon coordination with small molecules that can transfer excitation energy to the metal. This report is the first to describe the coordination of CPA with lanthanide metals, resulting in a substantial enhancement of their luminescence. The luminescence expressed was dependent upon the type of lanthanide, its concentration, and the environment (solvent, water content, pH). Based upon the phenomenon, a competitive assay was also developed wherein terbium (Tb3+) and a series of metal cations competed for binding with CPA. With increasing cation concentration, the luminescence of the CPA/Tb3+ complex was inhibited. The chlorides of ten metals were tested. Inhibition was best with Cu2+, followed by Co2+, Al3+, Fe3+, Mn2+, Au3+, Mg2+, and Ca2+. Two cations in oxidation state one (Na⁺, K⁺) did not inhibit the interaction significantly. The interaction of CPA with lanthanides provides a novel recognition assay for this toxin. It also provides a novel way to probe the binding of CPA to metals, giving insights into CPA’s mechanism of action.

An Imaging Surface Plasmon Resonance Biosensor Assay for the Detection of T-2 Toxin and Masked T-2 Toxin-3-Glucoside in Wheat

A sensitive, rapid, and reproducible imaging surface plasmon resonance (iSPR) biosensor assay was developed to detect T-2 toxin and T-2 toxin-3-glucoside (T2-G) in wheat. In this competitive assay, an amplification strategy was used after conjugating a secondary antibody (Ab₂) with gold nanoparticles. Wheat samples were extracted with a methanol/water mixture (80:20 v/v), then diluted with an equal volume of primary antibody (Ab₁) for analysis. Matrix-matched calibration curves were prepared to determine T-2 toxin and T2-G. Recovery studies were conducted at three spiking levels in blank wheat. Mean recoveries ranged from 86 to 90%, with relative standard deviations for repeatability (RSDr) of less than 6%. Limits of detection were 1.2 ng/mL of T-2 toxin and 0.9 ng/mL of T2-G, equivalent to their levels in wheat, of 48 and 36 µg/kg, respectively. The developed iSPR assay was rapid and provided enough sensitivity for the monitoring of T-2 toxin/T2-G in wheat. This is the first iSPR assay useful for detecting the "masked" T2-G in wheat.

MycoKey Round Table Discussions of Future Directions in Research on Chemical Detection Methods, Genetics and Biodiversity of Mycotoxins

MycoKey, an EU-funded Horizon 2020 project, includes a series of "Roundtable Discussions" to gather information on trending research areas in the field of mycotoxicology. This paper includes summaries of the Roundtable Discussions on Chemical Detection and Monitoring of mycotoxins and on the role of genetics and biodiversity in mycotoxin production. Discussions were managed by using the nominal group discussion technique, which generates numerous ideas and provides a ranking for those identified as the most important. Four questions were posed for each research area, as well as two questions that were common to both discussions. Test kits, usually antibody based, were one major focus of the discussions at the Chemical Detection and Monitoring roundtable because of their many favorable features, e.g., cost, speed and ease of use. The second area of focus for this roundtable was multi-mycotoxin detection protocols and the challenges still to be met to enable these protocols to become methods of choice for regulated mycotoxins. For the genetic and biodiversity group, both the depth and the breadth of trending research areas were notable. For some areas, e.g., microbiome studies, the suggested research questions were primarily of a descriptive nature. In other areas, multiple experimental approaches, e.g., transcriptomics, proteomics, RNAi and gene deletions, are needed to understand the regulation of toxin production and mechanisms underlying successful biological controls. Answers to the research questions will provide starting points for developing acceptable prevention and remediation processes. Forging a partnership between scientists and appropriately-placed communications experts was recognized by both groups as an essential step to communicating risks, while retaining overall confidence in the safety of the food supply and the integrity of the food production chain.

Multiplexed Biosensors for Mycotoxins

Significant progress has been made in the development of biosensors that can be used to detect low-MW toxins produced by fungi (mycotoxins). The number of formats that have been investigated is impressive and is an indication of the importance attached to finding easy-to-use, accurate, and rapid methods for detecting these toxins in commodities and foods. This review explores the details of multiplexed biosensors based on many formats, including multiplexed immunoassays, suspension arrays, membrane-based devices (flow-through and immunochromatographic), and planar microarrays. Each assay format has its own strengths and areas that need improvement. Certain formats, such as multiplexed immunochromatographic devices, are well developed and relatively easy to use, and in some cases, commercial products are being sold. Others, such as the suspension arrays and microarrays, are laboratory-based assays that, although more complicated, are also more amenable to a larger scale of multiplexing. The diversity of such efforts and the multitude of formats under investigation suggest that multiple solutions will be found to satisfy the need for multiplexed toxin detection.

Development and Evaluation of Monoclonal Antibodies for Paxilline

Paxilline (PAX) is a tremorgenic mycotoxin that has been found in perennial ryegrass infected with Acremonium lolii. To facilitate screening for this toxin, four murine monoclonal antibodies (mAbs) were developed. In competitive indirect enzyme-linked immunosorbent assays (CI-ELISAs) the concentrations of PAX required to inhibit signal development by 50% (IC50s) ranged from 1.2 to 2.5 ng/mL. One mAb (2-9) was applied to the detection of PAX in maize silage. The assay was sensitive to the effects of solvents, with 5% acetonitrile or 20% methanol causing a two-fold or greater increase in IC50. For analysis of silage samples, extracts were cleaned up by adsorbing potential matrix interferences onto a solid phase extraction column. The non-retained extract was then diluted with buffer to reduce solvent content prior to assay. Using this method, the limit of detection for PAX in dried silage was 15 µg/kg and the limit of quantification was 90 µg/kg. Recovery from samples spiked over the range of 100 to 1000 µg/kg averaged 106% ± 18%. The assay was applied to 86 maize silage samples, with many having detectable, but none having quantifiable, levels of PAX. The results suggest the CI-ELISA can be applied as a sensitive technique for the screening of PAX in maize silage.

Signal amplification using colloidal gold in a biolayer interferometry-based immunosensor for the mycotoxin deoxynivalenol

Deoxynivalenol (DON) is a toxin produced by certain species of Fusarium fungi that can infest wheat, barley and corn. The fungi cause diseases in crops worldwide and some of the secondary metabolites, such as DON, can adversely affect animal health and food safety. To monitor DON in wheat rapidly, a biosensor using the principle of biolayer interferometry (BLI) was developed. The signal from the sensor was substantially amplified through the use of a primary antibody-colloidal gold conjugate. The amplification was much greater in the presence of wheat matrix than in buffered solution, suggesting matrix components may have contributed to the enhancement. The improved signal provided by the amplification allowed for the development of rapid qualitative and quantitative assays. The limit of detection of the method was 0.09 mg kg(-1); the limit of quantitation was 0.35 mg kg(-1). Recovery from wheat spiked over the range from 0.2 to 5 mg kg(-1) averaged 103% (RSD = 12%). The quantitative assay compared favourably (r(2) = 0.9698) with a reference chromatographic method for 40 naturally contaminated wheats. The qualitative assay was able to classify accurately the same group of 40 samples as either above or below a 0.5 mg kg(-1) threshold. These results suggest that the BLI technique can be used to measure DON in wheat rapidly.

Observation of T-2 toxin and HT-2 toxin glucosides from Fusarium sporotrichioides by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS)

The trichothecenes produced by solid and liquid cultures of Fusarium sporotrichioides were evaluated with high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). Along with the expected T-2 toxin HT-2 toxin and neosolaniol, two additional compounds were detected, which had ions 162 m/z higher than those in the mass spectra of T-2 toxin or HT-2 toxin. Fragmentation behavior of these two compounds was similar to that of T-2 toxin and HT-2 toxin. Based on LC-MS/MS behavior, it is proposed that the two compounds are T-2 toxin 3-O-glucoside and HT-2 toxin 3-O-glucoside. Production of the two glucosides was measured in kernels from wheat and oat inoculated with F. sporotrichiodes, as well as in cultures grown in liquid media and on cracked corn or rice. Production of glucosides in wheat and oats suggest that they may also be present in naturally contaminated cereals.

Detection of deoxynivalenol using biolayer interferometry

Biolayer interferometry allows for the real time monitoring of the interactions between molecules without the need for reagents with enzymatic, fluorescent, or radioactive labels. The technology is based upon the changes in interference pattern of light reflected from the surface of an optical fiber when materials bind to the tip of the fiber. The technique represents an alternative to technologies such as surface plasmon resonance, with an advantage in that the flow of extracts through small capillaries is not required. In this report, a deoxynivalenol-bovine serum albumin (DON-BSA) conjugate was non-covalently immobilized to the surface of aminopropylsilane sensors and the change in interference pattern resulting from the binding of DON-specific antibodies was measured. The basis for the assay was the competition between DON and the immobilized DON-BSA for binding to limited amounts of antibody. The technique was used to measure DON in extracts of spiked whole wheat flour, with a limit of detection of 0.10 mg DON/kg. Matrix interferences were an issue, and adequate quantification required using matrix-matched standards. When samples were tested with sensors that had not been conditioned to remove loosely attached DON-BSA, the recoveries at five spiking levels over the range from 0.2 to 5 mg/kg averaged 108.8% [relative standard deviation (RSD) 16.0%]. Using sensors that had been conditioned lowered the average recovery (101.4%) and improved the RSD (13.2%). This suggests that conditioning the sensors helped reduce a bias in the assay towards overestimation. These results, and the ease with which assays can be conducted, suggest further exploration of this technology for detection of mycotoxins is warranted.

Use of cyclodextrins as modifiers of fluorescence in the detection of mycotoxins

Cyclodextrins, cyclic oligosaccharides composed of amylose subunits, are known to interact with mycotoxins. The interactions may be useful to analytical chemists by altering the properties of the mycotoxin of interest, namely the chromatographic properties, electrophoretic properties, fluorescence, or absorption of these fungal metabolites. Practical applications of these effects have been the incorporation of cyclodextrins into high-performance liquid chromatography and capillary electrophoresis methods for mycotoxin detection. Specific mycotoxins include those with a native fluorescence such as the aflatoxins, ochratoxin A (OTA) and zearalenone (ZEN) as well as those that can be rendered fluorescent through derivatization, such as T-2 toxin. The literature describing the applications of cyclodextrins in mycotoxin analysis is reviewed and an attempt to extend the use of cyclodextrins to the detection of labelled T-2 toxin is presented. Twenty cyclodextrins were evaluated for their ability to enhance the fluorescence emission of T-2 toxin derivatized with pyrene-1-carbonyl cyanide (T2-Pyr). This evaluation revealed that heptakis (2,6-di-O-methyl)-beta-cyclodextrin (DIMEB), in particular, enhanced T2-Pyr fluorescence. DIMEB was used as a buffer modifier in a capillary electrophoresis-laser-induced fluorescence (CE-LIF) method for detecting T-2 in maize. Because of the effects that certain cyclodextrins have, especially under aqueous conditions, they may make useful additives for a variety of mycotoxin analytical methods.

Development of monoclonal antibodies for the fusarin mycotoxins

The fusarins are a group of mycotoxins produced by fungi that commonly infest cereal crops, in particular by the fungus Fusarium verticillioides. This group of compounds is characterized by a substituted 2-pyrrolidone ring attached to a 12-carbon polyunsaturated backbone. Several of the fusarins contain an epoxide substitution on the pyrrolidone ring and are highly mutagenic. This paper describes the development of seven monoclonal antibodies and immunoassays for detecting fusarins C and A. Fusarin C was isolated and conjugated to ovalbumin to produce the immunogen. Competitive indirect enzyme-linked immunosorbent assays (CI-ELISAs) were developed based upon the isolated monoclonal antibodies. The concentrations of fusarin C able to inhibit colour development by 50% (IC(50)) in CI-ELISAs were 1.0, 2.0, 3.6, 23.4, 28.9, 31.4, and 66.7 ng ml(-1) for clones 1-38, 1-30, 1-5, 1-7, 1-43, 1-25, and 1-21, respectively. Cross-reactivity with fusarin A was 44.8, 51.4, 41.1, 174.0, 62.6, 78.2, and 98.0% for clones 1-38, 1-30, 1-5, 1-7, 1-43, 1-25, and 1-21, respectively. Given the sensitivity of these antibodies for fusarins it is expected that, with further development, they may be useful for detecting fusarins at relevant levels in foods.

Extraction of aflatoxins B1 and G1 from maize by using aqueous sodium dodecyl sulfate

Aflatoxins are potent carcinogens produced by certain Aspergillus fungi. The aflatoxins were first discovered in the 1960s, and since then have been found to be distributed worldwide in a variety of commodities, foods, and feeds. Many of the early techniques for detecting aflatoxins involved extraction with halogenated solvents. With the increased availability and use of reversed-phase solid-phase extraction cartridges and the availability of immunoaffinity columns, aqueous mixtures of nonhalogenated solvents have been frequently used. To further reduce the need for solvents, we examined the effects of eliminating solvents during the extraction of maize, using aqueous mixtures of the detergent sodium dodecyl sulfate. After extraction and filtration, aflatoxins B1 (AFB1) and G1 (AFG1) were isolated by using commercially available immunoaffinity columns. The isolated AFB1 and AFG1 were derivatized with trifluoroacetic acid before separation by liquid chromatography with fluorescence detection. In spiked maize, the limits of detection were 0.5 and 1 ng/g for AFB1 and AFG1, respectively. Recoveries of AFB1 from maize spiked at 1-20 ng/g averaged 87.5% (range, 76.3-99.0%), with an average repeatability relative standard deviation (RSDr) of 4.0%. Recoveries of AFG1 from maize spiked at 2-20 ng/g averaged 80.4% (range, 70.3-85.8%), with an average RSDr of 3.5%. This is the first reported demonstration of an effective solvent-free extraction of aflatoxins from maize at ambient pressure, and this extraction procedure may serve to help reduce solvent consumption during aflatoxin analysis.

Synthesis and evaluation of molecularly imprinted polymers as sorbents of moniliformin

Moniliformin is a low molecular weight mycotoxin that has worldwide potential to contaminate cereal grains. Although several traditional methods have been developed to detect moniliformin, the lack of anti-moniliformin antibodies has created a need for materials that recognize moniliformin at the molecular level through a binding mechanism. To address this issue, the authors synthesized molecularly imprinted polymers that bind moniliformin. Imprinted and non-imprinted polymers were evaluated by equilibrium binding assays and moniliformin concentrations were measured by LC analysis using ultraviolet light detection. Successful polymers were imprinted with toxin analogues as the templates; non-imprinted polymers exhibited minimal binding in acetonitrile under the assay conditions. Selected imprinted polymers also bound moniliformin in ethanol, methanol and dimethyl formamide. Significant differences in moniliformin binding by the polymers were dependent on polymer composition, and these differences were highly dependent on the template used to imprint the polymer. Polymers were further evaluated as sorbents for molecularly imprinted solid-phase extraction (MISPE), and an imprinted polymer was used for preconcentration and clean-up of a moniliformin spiked corn extract.

Relationships among resistances to fusarium and Aspergillus ear rots and contamination by fumonisin and aflatoxin in maize

ABSTRACT Fusarium verticillioides, F. proliferatum, and Aspergillus flavus cause ear rots of maize and contaminate the grain with mycotoxins (fumonisin or aflatoxin). The objective of this study was to investigate the relationships between resistance to Fusarium and Aspergillus ear rots and fumonisin and aflatoxin contamination. Based on a previous study of 143 recombinant inbred lines from the cross NC300 x B104, 24 lines with the highest and 24 lines with the lowest mean fumonisin concentration were selected for further evaluation. Paired plots of each line were inoculated with F. verticillioides and F. proliferatum or with A. flavus in replicated trials in 2004 and 2005 in Clayton, NC, and College Station, TX. The low-fumonisin group had significantly lower levels of fumonisin, aflatoxin, and Fusarium and Aspergillus ear rots. Across year-location environments, all four traits were significantly correlated; the genotypic correlation (r(G)) ranged from r(G) = 0.88 (aflatoxin and Aspergillus ear rot) to r(G) = 0.99 (Fusarium and Aspergillus ear rots). Quantitative trait loci (QTLs) were identified and their effects estimated. Two QTLs affected both toxin concentrations, one QTL affected both ear rots, and one QTL affected Aspergillus and Fusarium rots and fumonisin. These results suggest that at least some of the genes involved in resistance to ear rots and mycotoxin contamination are identical or genetically linked.

Capillary electrophoresis of the mycotoxin zearalenone using cyclodextrin-enhanced fluorescence

Certain of the cyclodextrins are capable of significantly enhancing the native fluorescence of the estrogenic mycotoxin zearalenone (ZEN). Twenty-two cyclodextrins (CDs) were screened for their ability to enhance the fluorescence of ZEN in a capillary electrophoresis-laser induced fluorescence (CE-LIF) format. Of the CDs that were examined heptakis (2,6-di-O-methyl)-beta-CD gave the greatest enhancement. The heptakis (2,6-di-O-methyl)-beta-CD was applied to the development of a CE-LIF method for detection of ZEN in maize. The resulting method was capable of detecting ZEN with a limit of quantitation of 5 ng/g maize. Recoveries of ZEN from maize spiked over the range from 5 ng/g to 500 ng/g averaged 103.1+/-8.5% (n=20). The CE-LIF method will be useful for future studies of ZEN in maize.

Measurement of T-2 and HT-2 toxins in eggs by high-performance liquid chromatography with fluorescence detection

T-2 toxin is a mycotoxin produced by several species of common fungi capable of infesting human food and animal feeds. Lower-quality feeds given to chickens may be contaminated with T-2 toxin, which may affect their health. The literature suggests that T-2 toxin is transmitted from the hen to the eggs. This article describes the development of a liquid chromatographic assay for T-2 and the related mycotoxin HT-2 in eggs. T-2 and HT-2 toxins were isolated from spiked eggs with a tandem charcoal-alumina-Florisil column and immunoaffinity column cleanup. The isolated toxins were derivatized with the fluorophore 1-anthroyl nitrile, separated by high-performance liquid chromatography, and quantitated by fluorescence. The limit of detection of the method was 1 ng ml(-1) (parts per billion) of T-2 and HT-2 in whole (with shell removed) eggs. The limit of quantitation for both toxins was 5 ng ml(-1). Recoveries from spiked eggs over the range from 5 to 50 ng ml(-1) averaged 89.2% for T-2 and 100.3% for HT-2, with coefficients of variation of 3.5 and 8.2%, respectively. This method is sensitive enough to be used to check for the presence of T-2 or HT-2 toxins in eggs.

Maize ear rot and moniliformin contamination by cryptic species of Fusarium subglutinans

Fusarium subglutinans causes maize ear rot and contaminates grain with the mycotoxin moniliformin. Previous DNA sequence analysis divided F. subglutinans from maize into two cryptic species, designated groups 1 and 2. Here, it was determined whether the two groups differ in the agriculturally important traits of virulence on maize and moniliformin production in planta. Thirty-seven strains from U.S. maize were assigned to groups 1 and 2 by DNA sequence analysis. In field tests, all strains were highly virulent on maize inbred B73 and four maize hybrids. In planta, 82% of group 1 strains and 25% of group 2 strains produced high levels (100-1500 microg/g) of moniliformin. All group 2 strains from more northern states produced little or no moniliformin (0-5 microg/g). These data indicate that moniliformin production is highly variable in F. subglutinans from U.S. maize and that production may not be required for the fungus to cause maize ear rot.

Indirect competitive immunoassay for detection of aflatoxin B1 in corn and nut products using the array biosensor

Because of the potential health risks of aflatoxin B1 (AFB1), it is essential to monitor the level of this mycotoxin in a variety of foods. An indirect competitive immunoassay has been developed using the NRL array biosensor, offering rapid, sensitive detection and quantification of AFB1 in buffer, corn and nut products. AFB1-spiked foods were extracted with methanol and Cy5-anti-AFB1 added to the resulting sample. The extracted sample/antibody mix was passed over a waveguide surface patterned with immobilized AFB1. The resulting fluorescence signal decreased as the concentration of AFB1 in the sample increased. The limit of detection for AFB1 in buffer, 0.3 ng/ml, was found to increase to between 1.5 and 5.1 ng/g and 0.6 and 1.4 ng/g when measured in various corn and nut products, respectively.

Evaluation of Food-Grade Dent Corn Hybrids for Severity of Fusarium Ear Rot and Fumonisin Accumulation in Grain

Fumonisins produced by Fusarium verticillioides (syn = F. moniliforme) and F. proliferatum have been associated with potentially serious toxicoses of animals and humans. Thus, hybrids with low fumonisin accumulation in grain will be valuable for the production of corn-based human food products. We evaluated 68 food-grade dent corn hybrids for severity of Fusarium ear rot and fumonisin accumulation in grain in inoculated trials in Urbana, IL in 2000 and 2001. Our inoculation technique was successful in initiating fumonisin accumulation that allowed discrimination among hybrids. We identified several hybrids that could have acceptable levels (<4 μg/g) of fumonisin accumulation in Illinois in most years. Twenty-six hybrids with low or high fumonisin accumulation in 2000 were reevaluated in noninoculated trials at three locations in Illinois in 2001. Fumonisin concentration in grain at all three locations was relatively low; thus, separation of hybrids was poor. At two locations, those hybrids with the highest fumonisin concentration in grain also had high concentrations following inoculation. However, one hybrid that had relatively low fumonisin concentration following inoculation had unacceptable levels of fumonisin (5 μg/g) in natural conditions. Therefore, hybrids need to be evaluated by inoculation and further evaluated at locations where the environment favors fumonisin accumulation.

Detection of moniliformin in maize using capillary zone electrophoresis

Moniliformin is a mycotoxin produced by certain fungi pathogenic to maize. It is capable of causing disease in domestic animals, possibly through inhibition of pyruvate dehydrogenase. Testing for MON commonly involves extraction of maize, isolation of moniliformin using solid-phase extraction columns and detection with high-performance liquid chromatography (HPLC) or gas chromatography. A capillary zone electrophoresis-diode array detection (CZE-DAD) method for determination of moniliformin in maize is reported. The extraction and isolation procedures are similar to those of a commonly used HPLC method, while the detection step requires only 10 min. Sixty-three samples of maize were tested by an established HPLC method using absorbance at 229 nm (HPLC-ultraviolet light) and by the CZE-DAD method. The limit of detection of the CZE-DAD method was 0.1 microg MON g(-1) maize compared with 0.05 microg g(-1) for the HPLC-ultraviolet light method. The CZE-DAD method gave good agreement with the HPLC-ultraviolet light method for samples tested at levels up to 1500 microg g(-1), with a linear regression of r(2) = 0.996.