Survey of natural occurrence of trichothecene mycotoxins and zearalenone in Korean cereals harvested in 1992 using gas chromatography/mass spectrometry

Analytical Methods for Trichothecenes Surveillance — An Overview Over the Period 1990—2000

This article reviews some aspects of analytical methods used to determine the occurrence of type A and B trichothecenes in grains and foodstuffs and their trends during the decade 1999—2000. A pronounced tendency to use extraction solvents less toxic than chloroform became evident. There was not a prevalent clean up process that pointed there were problems to obtain good recoveries of those mycotoxins. Taking into account the mean values of contamination found in the literature and the provisional maximum tolerable daily intake, a methodology suitable for a surveillance work should have a limit of quantification not greater than 50 μg/kg for deoxynivalenol and less than 10 μg/kg for T-2 and HT-2 toxins. Therefore, gas chromatography or thin layer chromatography could be used for type B trichothecenes while for type A trichothecenes, gas chromatography with electron capture or mass spectrometric detectors is the mandatory quantification method.

A novel mycotoxin purification system using magnetic nanoparticles for the recovery of aflatoxin B1 and zearalenone from feed

In this study, we developed a novel tool for purifying two mycotoxins, aflatoxin B1 (AFB1) and zearalenone (ZEN), in feed. This system utilized monoclonal antibodies (mAbs) against AFB1 and ZEN, and magnetic nanoparticles (MNPs). Among ten MNPs with different diameters and functional groups, a 100-nm diameter MNP (fMA) conjugated to an amine group (-NH₂) was found to be optimum for coupling with mAbs. The optimal mAb concentrations for coupling to the fMA along with mycotoxin purification capacities of the fMA-mAb conjugates (fMA-AFB1 and fMA-ZEN) were determined. A comparison of mean recovery rates (from corn and product X feed) between the fMA-mAb conjugates and immunoaffinity columns (IAC-AFB1 and IAC-ZEN) showed that the rate for fMA-AFB1 (90~92% and 81~88%) was higher (p > 0.05) than that of IAC-AFB1 (81~84% and 72~78%) for AFB1 (5, 10, 15 ng/mL), and the rate for fMA-ZEN (99~100% and 92~94%) was significantly higher (p < 0.01) than that of IAC-ZEN (86~88% and 81~88%) for ZEN (10, 25, 50 ng/mL) except at a concentration of 10 ng/mL, demonstrating the remarkable purification efficiency of the novel fMA-mAb method. Additionally, mycotoxin purification was much faster using our novel method (approx. 5 min) than the IAC-based technique (> 30 min). This study suggests that the novel purification system we developed would be a useful tool for monitoring and regulating mycotoxin contamination in feed, and replace IAC methods.

Determination of nivalenol and deoxynivalenol by liquid chromatography/atmospheric pressure photoionization mass spectrometry

Fusarium species, a plant pathogenic fungus of wheat and other cereals, produces toxic metabolites such as nivalenol (NIV) and deoxynivalenol (DON). Control of contamination by these toxins is very difficult, and a continuous survey of the occurrence is necessary for these toxins. Thus, the accurate and convenient determination of the cereals contaminated with these toxins is important for the supply of safe foods. A selective analytical method based on high-performance liquid chromatography, combined with atmospheric pressure photoionization (APPI) mass spectrometry, has been developed for simultaneous determination of NIV and DON. The parameters investigated for the optimization of APPI were the ion source parameters fragmentor voltage, capillary voltage, and vaporizer temperature, and also mobile phase composition and flow rate. Furthermore, chemical noise and signal suppression of analyte signals due to sample matrix interference were investigated for APPI. The results indicated that APPI provides lower matrix effect and the correlation coefficient of NIV and DON in the range 0.2-100 ng x mL(-1) was above 0.999. Recoveries of NIV and DON in wheat ranged from 86 to 107% and limits of detection of NIV and DON were 0.20 ng x g(-1) and 0.39 ng x g(-1), respectively. In addition, the proposed method was applied for the analysis of naturally contaminated wheat samples. APPI was found to offer lower matrix effect and was a convenient technique for routine analysis of NIV and DON residues in wheat at trace levels.

Fusariotoxin transfer in animal

Mycotoxin fusariotoxins, essentially represented by trichothecenes, zearalenone and fumonisins, are widely scattered in cereals and their products. Human and animals are particularly concerned by toxicity consecutive to oral chronic exposure. Human exposure can be direct via cereals or indirect via products of animals having eaten contaminated feed. As this alimentary risk is considered as a major problem in public health, it is thus of great importance to determine bioavailability, metabolic pathways and distribution of these mycotoxins in animal and human organism. Most studies indicate that fusariotoxins can be rapidly absorbed in the small intestine but the mechanisms involved remain unclear. Except NIV, fusariotoxins can be partly metabolised into more hydrophilic molecules in digestive tract or liver. Fumonisins present different behaviour as they seem very few and slowly absorbed and metabolised. The main part of absorbed fusariotoxins shows a rapid elimination within 24h after ingestion, followed by a slower excretion of small amounts. However, traces of fusariotoxins or their derivates can be found in animal products. This manuscript, reviewing literature published on fusariotoxin transfer, highlights that too little data are available to correctly appreciate fusariotoxin transfer in organism. Further studies focusing on mechanisms involved in the transfer are needed before clarifying risk assessment for human health.

Up-regulation of macrophage inflammatory protein-2 and complement 3A receptor by the trichothecenes deoxynivalenol and satratoxin G

The trichothecenes are a group of mycotoxins that target leukocytes and have a wide range of immunomodulatory effects. Differential display analysis was applied to assess the effects of the trichothecenes deoxynivalenol (vomitoxin, DON) and satratoxin G (SG), on mRNA in the RAW 264.7 macrophage cell line. Cells were incubated with DON (1 microg/ml) or SG (5 ng/ml) for 2 h and total RNA then subjected to RT-PCR with a set of oligo(dT) primers. Resultant cDNA was amplified using an oligo (dT) downstream primer and an arbitrary decanucleotide upstream primer to make 35S-labeled PCR products. After separation of the products in denaturing polyacrylamide gel, 23 differentially expressed cDNA fragments were isolated and sequenced. Two of these were identified as known genes, namely, macrophage inflammatory protein-2 (MIP-2), a potent neutrophil chemoattractant involved in tissue injury and inflammation, and complement 3a receptor (C3aR), a proinflammatory mediator. Both MIP-2 and C3aR mRNAs were up-regulated by DON while only MIP-2 mRNA was induced by SG. Using commercially available antibodies, MIP-2 protein was also found to be induced by both DON and SG in RAW 264.7 cell cultures. When mice were treated with DON (12.5 mg/kg), splenic MIP-2 mRNA and serum MIP-2 levels were increased. MIP-2 mRNA and serum MIP-2 levels were synergistically increased when mice were co-treated with DON and LPS. Up-regulation of MIP-2 and C3aR are consistent with previous reports of trichothecene-induced inflammatory gene up-regulation and suggest that the specific genes affected may depend on trichothecene structures.

Natural co-occurrence of aflatoxin B1, fumonisin B1 and ochratoxin A in barley and corn foods from Korea

A survey for aflatoxin B1 (AFB1), fumonisin B1 and ochratoxin A (OTA) was conducted on 127 samples that included 30 food-grade barley, 32 barley foods, 18 food-grade corn and 47 corn foods, randomly collected during 1998-99 in Seoul, Korea. The presence of mycotoxins was analysed by direct competitive enzyme-linked immunosorbent assay (ELISA), and most of the positive samples from ELISA were confirmed using high-performance liquid chromatography (HPLC). Recoveries of AFB1 and OTA spiked at 10 ng g(-1) and FB1 spiked at 50 ng g(-1) were 106, 87 and 105% by ELISA, whereas those by HPLC were 80, 79 and 84%, respectively. Detection limits by ELISA for AFB1, FB1 and OTA were 1, 5 and 5 ng g(-1), and those by HPLC were 0.6, 35 and 1 ng g(-1). Naturally occurring AFB1, FB1 and OTA were found in 4/32 (12%), 2/32(6%) and 4/32 (12%) samples of barley foods with an average of 26, 16 and 9 ng g(-1), respectively. AFB1 and FB1 in corn foods were detected in 4/47 (8%) and 9/47 (19%) samples with the average being 20 and 74 ng g(-1), while no OTA was found in any corn foods samples. No AFB1, FB1 or OTA was detected in any of food-grade barley and corn samples. This is the first report on the natural co-occurrence of AFB1 and FB1 in barley and corn foods as well as on surveillance of OTA in Korea.

Identification by PCR of Fusarium culmorum strains producing large and small amounts of deoxynivalenol

Thirty deoxynivalenol-producing F. culmorum strains, isolated from wheat grains, were incubated in vitro and analyzed for trichothecene production. Seventeen strains produced more than 1 ppm of deoxynivalenol and acetyldeoxynivalenol and were considered high-deoxynivalenol-producing strains, whereas 13 F. culmorum strains produced less than 0.07 ppm of trichothecenes and were considered low-deoxynivalenol-producing strains. For all strains, a 550-base portion of the trichodiene synthase gene (tri5) was amplified and sequenced. According to the tri5 data, the F. culmorum strains tested clustered into two groups that correlated with in vitro deoxynivalenol production. For three high-producing and three low-producing F. culmorum strains, the tri5-tri6 intergenic region was then sequenced, which confirmed the two separate clusters within the F. culmorum strains. According to the tri5-tri6 sequence data, specific PCR primers were designed to allow differentiation of high-producing from low-producing F. culmorum strains.

Comparison of extraction and clean-up procedures for analysis of zearalenone in corn, rice and wheat grains by high-performance liquid chromatography with photodiode array and fluorescence detection

The aim of this work was the optimization of some procedures usually used in the analysis of zearalenone (ZEA) in corn and other cereals by high-performance liquid chromatography (HPLC) with photodiode array and/or fluorescence detection. The comparison of five extraction solvents is presented. Three solid-phase extraction cartridges (C-18, silica, Florisil) and immuno-affinity columns were also compared to obtain the best recovery of the mycotoxin with the minimal presence of co-extractives in the chromatograms. Mixtures of methanol-1% aqueous NaCl (80.20 or 60:40 v/v) were the best extraction solvents. Florisil provided higher recovery of ZEA than C-18, and silica proved unsuitable. The immuno-affinity column was very efficient in cleaning the extracts, but its sample capacity was lower than that of SPE columns due to saturation. The mobile phase (methanol-water 80:20 v/v) gave a low retention time for ZEA (approximately 5 min), high sensitivity and acceptable separation between this mycotoxin and alpha-zearalenol. The optimized protocol is straightforward, provides high ZEA recoveries in spiked corn (mean 102.4%), has an acceptable sensitivity and has a lack of interference with fluorescence detection (detection limit 4 ng ZEA g(-1) corn). The photodiode array detector was useful, except at very low ZEA levels, to confirm the identity of the mycotoxin. The method was applied to search for ZEA accumulation in corn, wheat and rice grains inoculated with selected strains of Fusarium graminearum, F. oxysporum and method was applied to search for ZEA accumulation in corn, wheat and rice grains inoculated with selected strains of Fusarium graminearum, F. oxysporum and F. culmorum.

Determination of deoxynivalenol in wheat-based breakfast cereals marketed in Portugal

Deoxynivalenol (DON), also known as vomitoxin, is one of a group of closely related secondary fungal metabolites--the trichothecenes--and is produced predominantly by several species of the genus Fusarium, especially Fusarium graminearum. The present study was carried out to evaluate the natural occurrence of DON in different kinds of wheat-based breakfast cereals widely consumed by the population. A total of 88 commercially available samples of wheat-based breakfast cereals were randomly collected from different supermarkets in Lisbon, Portugal. The samples were analyzed using immunoaffinity column, and DON was quantified by liquid chromatography. Detection limit was 100 microg/kg. Average recovery of DON was 80%. Of 88 analyzed samples, 72.8% contained levels of DON between 103 and 6,040 microg/kg, with mean level of 754 microg/kg, and 24 samples (27.2%) were not contaminated (< 100 microg/kg). These results indicate an incidence of this mycotoxin in these products, and the authors suggest a monitoring for the prevention of molds and mycotoxins. This is the first report in Portugal on natural contamination with DON in wheat-based breakfast cereals.

Toxigenic potential of Fusarium culmorum strains isolated from French wheat

Sixty F. culmorum strains were isolated from wheat grains collected from different wheat-growing areas in France and from different cultivars. The isolates were grown on autoclaved wheat grain to assess their ability to produce trichothecenes and zearalenone. Fungal biomass was evaluated through the ergosterol grain content. All the isolates produced zearalenone (0.39-1660 mg kg(-1)). Thirty-five of the 60 F. culmorum produced nivalenol (0.11-11.7 mg kg(-1)), 12 of 60 produced fusarenone X (0.05-8.42 mg kg(-1)), five of 60 produced 15-acetyldeoxynivalenol (0.48-27.7 mg kg(-1)), 13 of 60 produced 3-acetyldeoxynivalenol (0.07-21.0 mg kg(-1) and 24 of 60 produced deoxynivalenol (0.92-51.9 mg kg(-1)). According to the results, the distribution of the different chemotypes as well as the high and the low mycotoxin-producing Fusarium strains could not be associated to geographical origin.

The occurrence of HT-2 toxin and other trichothecenes in Norwegian cereals

A total of 449 grain samples, 102 barley, 169 wheat and 178 oat samples were collected from different regions of Norway from 1996-1998 crops, mainly from grain loads and silos. The samples were analysed for type A and B trichothecenes, the largest groups of mycotoxins produced by the Fusarium species, by gas chromatography with mass spectrometric detection (GC-MS). Factors affecting the presence of the different trichothecenes are discussed. Deoxynivalenol (DON) and HT-2 toxin were the trichothecenes most frequently detected, followed by T-2 toxin, nivalenol, and scirpentriol, scirpentriol being detected only in seven samples (> 20 micrograms/kg). Oats were the grain species most heavily contaminated with an incidence (% > 20 micrograms/kg) and mean concentration of positive samples of 70% (115 micrograms/kg) for HT-2 toxin, 30% (60 micrograms/kg) for T-2 toxin, 57% (104 micrograms/kg) for DON, and 10% (56 micrograms/kg) for nivalenol. The corresponding values for barley were 22% (73 micrograms/kg), 5% (85 micrograms/kg), 17% (155 micrograms/kg) and 6% (30 micrograms/kg), and for wheat 1.2% (20 micrograms/kg), 0.6% (20 micrograms/kg), 14% (53 micrograms/kg) and 0% for HT-2, T-2, DON and nivalenol, respectively. Norwegian oats were found to contain HT-2 and T-2 toxin in concentrations that might be at threat to human health for high consumers of oats. The amount of DON was significantly lower than in the crop from previous years.

Evaluation of mycotoxin-contaminated cereals for their use in animal feeds in Hungary

In the period between December 5, 1991 and September 17, 1998, 760 maize, 367 wheat, 119 soybean, 222 barley, 85 bran, 32 triticale, 60 oat, 14 rye and 22 sunflower samples were investigated for the presence and concentration of seven fusariotoxins (T-2 toxin, zearalenone, deoxynivalenol, nivalenol, diacetoxyscirpenol, HT-2 toxin, fusarenone-X) and OTA. The comparison of analytical data with those of the relevant literature revealed that although the incidence rate and/or concentration of Fusarium mycotoxins and OTA in Hungarian-grown cereals is occasionally considerable, the position of the country is not worse that the average of countries. Our findings indicate that soybean tends to be good substrate for trichothecene-producing fungi and the rate of contamination is regarded as substantial. The commodities were assorted into one of three quality categories. The proportion of objectionable samples was only 3.0, 2.2, 2.3 and 1.7% in maize, wheat, barley and soybean samples, respectively. However, this low rate of objection might still be a source of great economic loss. The proportion of objectionable samples was much higher in the case of bran, oat and triticale (7.1, 6.7, and 6.3%, respectively). The results of the present investigation indicate a need for regular screening for mycotoxins of importance and individual appraisal of each commodity from the point of their use in animal feeds.

Quantification of deoxynivalenol in wheat using an immunoaffinity column and liquid chromatography

A simple and accurate method to quantify the mycotoxin deoxynivalenol (DON) in wheat is described. The method uses immunoaffinity chromatography for DON isolation and liquid chromatography (LC) for toxin detection and quantification. Wheat samples are extracted in water, filtered twice and applied to an immunoaffinity column. Following a water wash, DON is eluted from the column with methanol and injected onto an LC system with a UV detector for quantification. Test performance was evaluated in terms of antibody specificity, limit of detection, percentage recovery, precision, column capacity, assay linearity and comparison with the GC-electron-capture detection (ECD) method of Tacke and Casper. Specificity of the immunoaffinity column cleanup procedure was confirmed with only DON (>80%) and its 15-C derivatives (40-50%) being recognized by the antibody while 3-C DON derivatives, nivalenol, T-2 and fusarenon-X did not bind. The limit of detection is at least 0.10 microg/g. Percentage recovery for the entire assay range averages 90% with an average relative standard deviation of 8.3%. Naturally contaminated samples showed comparable precision. Column capacity was determined to be 3.3 microg. The assay showed a high degree of linearity (r2=0.999) and an optimum assay range of 0.10 to 10.0 microg/g. Comparative analysis of 28 naturally or artificially contaminated wheat samples using DONtest-HPLC and the GC-ECD method of Tacke and Casper showed that DONtest-HPLC is a statistically significant predictor of the GC-ECD method (r2=0.982).

Development and use of a reverse transcription-PCR assay to study expression of Tri5 by Fusarium species in vitro and in planta

The Tri5 gene encodes trichodiene synthase, which catalyzes the first reaction in the trichothecene biosynthetic pathway. In vitro, a direct relationship was observed between Tri5 expression and the increase in deoxynivalenol production over time. We developed a reverse transcription (RT)-PCR assay to quantify Tri5 gene expression in trichothecene-producing strains of Fusarium species. We observed an increase in Tri5 expression following treatment of Fusarium culmorum with fungicides, and we also observed an inverse relationship between Tri5 expression and biomass, as measured by beta-D-glucuronidase activity, during colonization of wheat (cv. Avalon) seedlings by F. culmorum. RT-PCR analysis also showed that for ears of wheat cv. Avalon inoculated with F. culmorum, there were different levels of Tri5 expression in grain and chaff at later growth stages. We used the Tri5-specific primers to develop a PCR assay to detect trichothecene-producing Fusarium species in infected plant material.

Thin-layer chromatography of mycotoxins and comparison with other chromatographic methods

This paper highlights the status of thin-layer chromatography (TLC) of mycotoxins in various sample matrices. The outstanding merits of TLC in the field of the qualitative and quantitative determination of mycotoxins have been briefed. A comparison between different TLC methods and TLC with HPLC, enzyme-linked immunosorbent assay and GC methods, etc. is made, in general.

Determination of zearalenone in corn by means of immunoaffinity clean-up and high-performance liquid chromatography with fluorescence detection

A rapid and accurate method to quantify zearalenone in corn is described. The method uses immunoaffinity chromatography for purification and high-performance liquid chromatography (HPLC) for detection and quantification of the toxin. Corn samples were extracted with acetonitrile-water (90:10, v/v) and the extract was diluted with water (1:10, v/v) and applied to a Vicam ZearalaTest immunoaffinity column. The column was washed with water and zearalenone was eluted with methanol and quantified by reversed-phase HPLC with fluorometric detection (lambda ex = 274 nm, lambda em = 440 nm) using acetonitrile-water-methanol (46:46:8, v/v) as mobile phase. Zearalenone recoveries from the ZearalaTest column were higher than 95%, and the column can hold a maximum of 4.0 micrograms of toxin. Average recoveries of zearalenone from corn spiked at levels of 0.1-10 micrograms/g ranged from 9 to 99.5%, with relative standard deviations of < 6%. The detection limit was 3 ng/g based on a signal-to-noise ratio of 3:1. Comparative analysis of 14 naturally contaminated samples using this method and the AOAC official method 985.18 showed a reasonable correlation (r = 0.87). Advantages of the immunoaffinity method as compared to the AOAC method are discussed.