High-performance liquid chromatographic determination of zearalenone and ochratoxin A in cereals and feed

Considerations in the preparation of laboratory samples for the analysis of ochratoxin A in wheat

A process used to prepare the test portion of ground wheat from the whole grain laboratory sample for ochratoxin A (OTA) analysis using dry comminution with homogenisation and sub-sampling via a rotary sample divider was developed and evaluated. With respect to OTA content, the developed process produced a homogeneous sample of ground wheat from 10 kg of whole grain. Relative standard deviations of the mean OTA concentration for five naturally contaminated wheat samples processed using the developed method ranged from 9% to 19% over a relevant concentration range of 1.7 to 7.6 mg/kg. Additional studies demonstrated that OTA was stable in ground wheat with moisture content between 12 to 13% for at least a year when stored at ambient temperatures. Further examination of the developed comminution and dividing procedure demonstrated that higher concentrations were measured in smaller sized particles, indicating that the accuracy and precision of OTA analyses could be affected by the particle size of ground wheat.

Determination of Penicillium mycotoxins in foods and feeds using liquid chromatography-mass spectrometry

New LC-MS (full scan) and LC-MS-MS (selected ion reaction monitoring) methods for the simultaneous determination of mycophenolic acid, griseofulvin, roquefortine C, chaetoglobosin B, verruculogen and penitrem A, and other Penicillium derived mycotoxins in food and feed samples are described. The methodologies involve sample extraction with acetonitrile-water, defatting with hexane and quantification using LC-MS with atmospheric pressure chemical ionisation or LC-MS-MS. Detector responses, for each of the methods and mycotoxins, were found to be linear over the range 10-1000 ng of mycotoxin/g of extracted food mixture material. The mean recoveries (n = 3 to 6) of the mycotoxins from spiked food mixture samples determined using MS and MS-MS detection were 87-116 and 91-112%, respectively, for mycophenolic acid, 104-109 and 91-112%, respectively, for griseofulvin, 70-85 and 75-110%, respectively, for roquefortine C, 94-109 and 81-116%, respectively, for chaetoglobosin B, 110-115 and 90-106%, respectively, for verruculogen and 78-97 and 99-108%, respectively, for penitrem A. RSDs varied from 5.6% at the 1000 ng/g level to 23.1% at the 10 ng/g level. The limits of detection for the mycotoxins using MS and MS-MS were 70 and 10 ng/g, respectively, for mycophenolic acid, 10 and 5 ng/g, respectivley, for griseofulvin, 50 and 20 ng/g, respectively, for roquefortine C, 25 and 20 ng/g, respectively, for chaetoglobosin B, 25 and 20 ng/g, respectively, for verruculogen and 10 and 5 ng/g, respectively, for penitrem A.

Fungal growth and fusarium mycotoxin content in isogenic traditional maize and genetically modified maize grown in France and Spain

Fungi of the genus Fusarium are common fungal contaminants of maize and are also known to produce mycotoxins. Maize that has been genetically modified to express a Bt endotoxin has been used to study the effect of insect resistance on fungal infection of maize grains by Fusarium species and their related mycotoxins. Maize grain from Bt hybrids and near-isogenic traditional hybrids was collected in France and Spain from the 1999 crop, which was grown under natural conditions. According to the ergosterol level, the fungal biomass formed on Bt maize grain was 4-18 times lower than that on isogenic maize. Fumonisin B(1) grain concentrations ranged from 0.05 to 0.3 ppm for Bt maize and from 0.4 to 9 ppm for isogenic maize. Moderate to low concentrations of trichothecenes and zearalenone were measured on transgenic as well as on non-transgenic maize. Nevertheless, significant differences were obtained in certain regions. The protection of maize plants against insect damage (European corn borer and pink stem borer) through the use of Bt technology seems to be a way to reduce the contamination of maize by Fusarium species and the resultant fumonisins in maize grain grown in France and Spain.

Rapid, low cost thin-layer chromatographic screening method for the detection of ochratoxin A in green coffee at a control level of 10 microg/kg

A thin-layer chromatographic (TLC) screening method was developed for the detection of ochratoxin A (OTA) in green coffee at a control level of 10 microg/kg. The method is based on extraction of OTA with a mixture of phosphoric acid and dichloromethane, purification by liquid-liquid partition into sodium hydrogen carbonate, separation by normal-phase TLC, and detection by visual estimation of fluorescence intensity under a UV lamp at 366 nm. The method was validated by performing replicate analyses of uncontaminated green coffee material spiked at 3 different levels of OTA (5, 10, and 20 microg/kg), and also by comparing results obtained on a series of test trial green coffees naturally contaminated with OTA (range 0.2 to 136.7 microg/kg) with those measured by a quantitative immunoaffinity/HPLC method. The agreement between the two methods was excellent, and neither false positive nor false negative results were recorded. This screening method is rapid, simple, robust, and very cheap, which makes it particularly well adapted for implementation in coffee-producing countries.

Application of manual and automated systems for purification of ochratoxin a and zearalenone in cereals with immunoaffinity columns

A manual vacuum manifold and an automated solid phase extraction (ASPEC) system were applied for purification of ochratoxin A and zearalenone in wheat, rye, barley, and oat samples with immunoaffinity columns followed by separation with a high-performance liquid chromatograph and fluorescence detection. The immunoaffinity columns for manual sample purification were purchased from a different manufacturer than were those for the automated system. The limit of detection (LOD) for the method for ochratoxin A with a vacuum manifold and ASPEC was 0.1 microg/kg. For the method for zearalenone, the LODs were 1.5 microg/kg with a vacuum manifold and 3 microg/kg with ASPEC. For the methods for ochratoxin A at spiking levels of 0.6 and 2.5 microg/kg, mean recoveries for different cereals varied from 68 to 106%. For the methods for zearalenone, mean recoveries varied from 78 to 117% at spiking levels of 9 and 25 microg/kg. The relative standard deviations of repeatability with various cereals employing both methods were 2-15 and 2-19% for ochratoxin A and zearalenone, respectively.

Chromatographic methods for the determination of ochratoxin A in animal and human tissues and fluids

This paper gives a review of chromatographic methods used for the determination of ochratoxin A (OA) in animal and human tissues and fluids. These methods are needed for example for monitoring studies of OA occurrence in the food chain and for studies dealing with the OA carry-over. In this survey, emphasis was given to HPLC methods. The review includes sampling, sample storage, extraction, spiking procedures, clean-up, detection and determination, and confirmation procedures. Emphasis is laid on special problems associated with the analysis of animal tissues and fluids.

Use of various clean-up procedures for the analysis of ochratoxin A in cereals

A rapid and reliable procedure has been developed for the determination of ochratoxin A in wheat and oats. The method consists of extraction of the sample with acidic chloroform, followed by defatting with n-hexane and finally, HPLC determination with fluorometric detection. Mean recoveries for wheat and oats spiked at levels between 1 and 100 micrograms/kg ranged from 80 to 104%. The limit of determination (field blank +6 sigma) was 0.8 micrograms/kg and the precision (within-laboratory relative standard deviation) ranged from 3 to 7%. The method was tested on 34 wheat and 34 oats samples. Ochratoxin A was confirmed in some positive samples by methyl ester formation and/or by clean-up of the extracts with immunoaffinity columns. The method was not appropriate for the analysis of barley (45 tested samples), rye (69 samples) or trout feed (13 samples). A false positive was recorded within the four positive barley samples and 18 false positives were recorded within the 21 positive rye samples whereas trout feed samples could not be analysed due to insufficient clean-up. The use of immunoaffinity columns made the analysis of trout feed and rye samples possible, providing excellent clean-up of the extracts with no false positive results and a good limit of determination (0.2 micrograms/kg).

An intercomparison of methods for the determination of ochratoxin A in pig kidney

The preparation of two pig kidney materials is described, together with a report on the results of an intercomparison study of methods to determine ochratoxin A levels in these materials. The materials were prepared, and the intercomparison study carried out within the European Commission. Measurements and Testing Programme, which is the successor of the Community Bureau of Reference (BCR). The materials were prepared from blank and naturally-contaminated pig kidneys and were freeze-dried. Details are given on the freeze-drying and packaging procedure, and the checks to ensure homogeneity and stability of the freeze-dried materials. The intercomparison study involved 20 European laboratories, which analysed the naturally-contaminated (freeze-dried) sample (ochratoxin A content approximately 10 micrograms/ kg based on fresh weight) and the 'blank' sample (ochratoxin A content < 0.6 microgram/kg based on fresh weight) using a variety of procedures for extraction and clean-up. All laboratories used HPLC as the determinative step. Recoveries were found to range from 43 to 128%. The study highlighted problems with recovery of spiked ochratoxin A from freeze-dried pig kidney material. There is a clear need to improve analytical performance, particularly with respect to the extraction efficiency from this type of matrix.

Ochratoxin A in wheat: certification of two reference materials

The preparation of two wheat reference materials and the certification of their ochratoxin A content is described. The materials were prepared and certified within the European Commission. Measurements and Testing Programme (M&T). The first and second phases of this project, two intercomparisons of procedures for the determination of ochratoxin A in wheat, at levels of approximately 13 micrograms/kg, and 7 micrograms/kg, respectively have already been reported. This paper describes the work carried out in certification of the ochratoxin A content (mass fraction) of two wheat reference materials: a blank wheat CRM 471, and a contaminated wheat, CRM 472. These materials were prepared for use in the second intercomparison referred to above and reported previously. Reference material CRM 472 was prepared from naturally-contaminated wheat blended with the blank wheat (CRM 471). Details are given of the milling, blending and packaging procedure, and the checks to ensure homogeneity and stability of the material. The certification exercise was carried out by 15 laboratories using a variety of extraction and clean-up procedures, and the certified ochratoxin A content (mass fraction) of CRM 471 was < 0.6 microgram/kg. The value for CRM 472 was 8.2 micrograms/kg with an uncertainty of 1.0 microgram/kg.

Determination of ochratoxin A in urine and faeces of swine by high-performance liquid chromatography

Sensitive methods for the determination of ochratoxin A in urine and faeces of swine are described. The samples were extracted with chloroform at pH < 2, and the extracts were cleaned up by a combination of solid-phase extraction and liquid-liquid partition. High-performance liquid chromatography with fluorescence detection was used for detection and determination. The detection limits were 0.3 ng/ml for urine and 1.5 ng/g for faeces. Recoveries of ochratoxin A from spiked samples of urine and faeces were 93% and 60%, respectively. Because of the low detection limit and the fast and relatively easy performance, the method for the determination of ochratoxin A in urine proved suitable for the estimation of possible contamination of live animals.

Ochratoxin A in wheat: an intercomparison of procedures

The Commission of the European Communities' Community Bureau of Reference (BCR) has undertaken a project to improve methodology and to prepare suitable certified reference materials in order to provide a basis for analytical quality control for the determination of ochratoxin A. The first phase of the project, an intercomparison of procedures for the determination of ochratoxin A in wheat at a level of approximately 13 micrograms/kg, is described. The study involved 24 European laboratories which analysed a naturally contaminated wheat and a 'blank' wheat sample (ochratoxin A content < 1 microgram/kg). The participants used a variety of procedures, including chloroform, methanol, toluene and ethyl acetate for extraction, and silica-, reversed phase- and immunoaffinity columns for clean-up. HPLC (one laboratory used TLC) was applied as the determinative step. Several performance characteristics were checked and the ochratoxin A content was determined. Recoveries were found to range from 25 to 100%. The coefficient of variation from all the results calculated on the basis of peak height was 23%. The study showed that the variation of results was influenced more by the clean-up step than by the extraction solvent. Some laboratories suffered significant day-to-day effects while others found difficulties with interfering peaks in the 'blank' material. It is planned for the next study to improve the recovery range, the clean-up step and the reproducibility (within-laboratory, between-days) and to check the influence of co-extractives from the matrix.

Multimycotoxin detection and clean-up method for aflatoxins, ochratoxin and zearalenone in animal feed ingredients using high-performance liquid chromatography and gel permeation chromatography

A sensitive and reliable method is described for the determination of aflatoxins B1, B2, G1 and G2, ochratoxin A and zearalenone in animal feed ingredients. A multi-toxin extraction and clean-up procedure is used, with dichloromethane-1 M hydrochloric acid (10:1) being used for the extraction and gel permeation chromatography being used for the clean-up. The liquid chromatographic method developed for the separation of the six mycotoxins involves gradient elution with a reversed-phase C18 column and fluorescence detection. Recoveries, repeatability and reproducibility have been determined on maize, palm and wheat. The detection limits varied depending on the type of feed.

Occurrence of the mycotoxins ochratoxin A, zearalenone and deoxynivalenol in feed components

The mycotoxin contamination of feed components used by the Dutch cooperative feed industry was surveyed to estimate the risk for animal production losses. Of 89 randomly and 6 selectively taken samples of raw materials harvested in 1988 and 1989 27% were contaminated with ochratoxin A (OCHRA), 31% with zearalenone (ZEA) and 20% with deoxynivalenol (DON). The mean content (microgram/kg) of all positive randomly taken samples was 18 (OCHRA), 62 (ZEA) and 630 (DON). The highest level (microgram/kg) for all samples was 120 (OCHRA) in barley, 3100 (ZEA) in corn cob mix and 1900 (DON) in maizegluten feed. The results of this survey show that feed components are often contaminated with mycotoxins. However, the contamination level could only sporadically cause production losses in animal husbandry.