Joint IDF-IUPAC-IAEA(FAO) interlaboratory validation for determining aflatoxin M1 in milk by using immunoaffinity clean-up before thin-layer chromatography

Inter-laboratory validation of liquid chromatography-tandem mass spectrometry multi-mycotoxin determination in animal feed - method transfer from the reference laboratory to regional laboratories

Introduction

The results are presented of the inter-laboratory validation of a liquid chromatography-tandem mass spectrometry method for the determination of eight mycotoxins (aflatoxin B1, deoxynivalenol, fumonisin B1, fumonisin B2, ochratoxin A, toxin T-2, toxin HT-2 and zearalenone) in animal feeds.

Material and Methods

This study was an essential part of the method's transfer from the National Reference Laboratory to six regional laboratories in Poland working in the official survey of mycotoxins in feed. The laboratories received a batch of standard solutions, blank samples and quality control materials on which to perform analysis with one procedure and different liquid chromatography-tandem mass spectrometry conditions.

Results

The validation results show good precision (reproducibility coefficient of variation 3.7-20.5%) and accuracy of the method (recovery 89-120% and trueness 94-103%) and sufficient skills of the laboratory personnel.

Conclusion

The study is an example of the successful transfer of the method among laboratories.

Monitoring of Aflatoxin M1 in Various Origins Greek Milk Samples Using Liquid Chromatography Tandem Mass Spectrometry

Aflatoxin M1(AFM1), a major metabolite of Aflatoxin B1(AFB1), has been identified as a potential contaminant in dairy products. Because of its possible carcinogenicity, the legislation limits as set by Commission Regulation (EC) No. 1881/2006 are very strict, namely 0.050 μg kg−1 in milk and 0.025 μg kg−1 in infant formulas. To meet these requirements, a sensitive and accurate method was developed, employing liquid chromatography tandem mass spectrometry (UPLC-MS/MS). Ιmmunoaffinity columns (R-Biopharm) were used for sample purification and preconcentration of the analyte of interest. The quantification of AFM1 was conducted using fortified milk samples, while Aflatoxin B2 (AFB2) was used as an internal standard (IS). The method was validated in terms of linearity, precision, trueness, limits of detection and quantification and uncertainty. The performance criteria for the method were evaluated based on European Commission Regulation (EC) No. 401/2006 and its most recent amendment, as well as the suggested criteria for revision by the EU Reference Laboratory for Mycotoxins and Plant Toxins. The recovery was in the range of 77.9–81.0% for all fortification levels (0.025–0.050–0.075 μg kg−1), with RSDR values (Relative Standard Deviation of intermediate precision) ranging from 6.1% to 12%. The method’s detection and quantification limits were 0.0027 μg kg−1 and 0.0089 μg kg−1, respectively. The occurrence of AFM1 was investigated in 40 samples of different animal origin (cow, goat and sheep milk) provided by Greek producers.

Detection Methods for Aflatoxin M1 in Dairy Products

Mycotoxins are toxic compounds produced mainly by fungi of the genera Aspergillus, Fusarium and Penicillium. In the food chain, the original mycotoxin may be transformed in other toxic compounds, reaching the consumer. A good example is the occurrence of aflatoxin M1 (AFM1) in dairy products, which is due to the presence of aflatoxin B1 (AFB1) in the animal feed. Thus, milk-based foods, such as cheese and yogurts, may be contaminated with this toxin, which, although less toxic than AFB1, also exhibits hepatotoxic and carcinogenic effects and is relatively stable during pasteurization, storage and processing. For this reason, the establishment of allowed maximum limits in dairy products and the development of methodologies for its detection and quantification are of extreme importance. There are several methods for the detection of AFM1 in dairy products. Usually, the analytical procedures go through the following stages: sampling, extraction, clean-up, determination and quantification. For the extraction stage, the use of organic solvents (as acetonitrile and methanol) is still the most common, but recent advances include the use of the Quick, Easy, Cheap, Effective, Rugged, and Safe method (QuEChERS) and proteolytic enzymes, which have been demonstrated to be good alternatives. For the clean-up stage, the high selectivity of immunoaffinity columns is still a good option, but alternative and cheaper techniques are becoming more competitive. Regarding quantification of the toxin, screening strategies include the use of the enzyme-linked immunosorbent assay (ELISA) to select presumptive positive samples from a wider range of samples, and more reliable methods-high performance liquid chromatography with fluorescence detection or mass spectroscopy-for the separation, identification and quantification of the toxin.

Development of an electrochemical biosensor for the detection of aflatoxin M1 in milk

We have developed an electrochemical immunosensor for the detection of ultratrace amounts of aflatoxin M(1) (AFM(1)) in food products. The sensor was based on a competitive immunoassay using horseradish peroxidase (HRP) as a tag. Magnetic nanoparticles coated with antibody (anti-AFM(1)) were used to separate the bound and unbound fractions. The samples containing AFM(1) were incubated with a fixed amount of antibody and tracer [AFM(1) linked to HRP (conjugate)] until the system reached equilibrium. Competition occurs between the antigen (AFM(1)) and the conjugate for the antibody. Then, the mixture was deposited on the surface of screen-printed carbon electrodes, and the mediator [5-methylphenazinium methyl sulphate (MPMS)] was added. The enzymatic response was measured amperometrically. A standard range (0, 0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.3, 0.4 and 0.5 ppb) of AFM(1)-contaminated milk from the ELISA kit was used to obtain a standard curve for AFM(1). To test the detection sensitivity of our sensor, samples of commercial milk were supplemented at 0.01, 0.025, 0.05 or 0.1 ppb with AFM(1). Our immunosensor has a low detection limit (0.01 ppb), which is under the recommended level of AFM(1) [0.05 μg L-1 (ppb)], and has good reproducibility.

The frequency of occurrence of aflatoxin M1 in milk on the territory of Vojvodina

Aflatoxin is one of the most common mycotoxins which can be found in milk. It represents a natural metabolite of aflatoxin B1 that occurs as a result of animal metabolism and the body's attempt to detoxificate it. It is excreted in milk, feces and urine of animals that consumed contaminated feed with aflatoxin B1. The carry-over from feed to milk depends on many factors, ranging from 0.3 to 6.2%. Aflatoxin M1 is in the first group of carcinogens according to the IRAC classification from 2002, but it is considered to have only 10% of carcinogenicity from its precursor aflatoxin B1. Legislation in member countries of European Union for this mycotoxin in milk intended for people is 0.05 ?g/l, while the rest of the countries that also have legislation for this mycotoxin allow the concentration that is ten times higher, and that is 0.5 ?g/l. In this paper, we have tried to provide on insight into the quality of milk, food often consumed by children, from the standpoint of mycotoxicology, and to compare the obtained data with data available from literature, from countries in the region that have similar climatic and agricultural conditions. From a total of 65 samples of processed milk, aflatoxin M1 was found in 18 samples and none of the samples exceeded the level of 0.05 ?g/l, which is allowed by the legislation of the European Union.