Aflatoxins

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Structural formula of (-) - aflatoxin B 1
Structural formula of aflatoxin G 1

Aflatoxins are naturally occurring mycotoxins that were first detected in the Aspergillus flavus mold . They were named accordingly after this species ("A-fla-toxin"). However, aflatoxins can also be produced by other species of the Aspergillus genus such as Aspergillus parasiticus , Aspergillus tamarii , Aspergillus nomius and other species.

A distinction is made between at least 20 naturally occurring aflatoxins, of which aflatoxin B 1 is considered to be the most dangerous for humans. In addition to aflatoxin B 1 , the toxins B 2 , G 1 and G 2 and the derivatives M 1 and M 2 found in milk are of greater importance.

features

Aflatoxins have an acute hepatotoxic effect ( liver dystrophy ) at concentrations around 10 µg / kg body weight , but have a carcinogenic effect on mammals , birds and fish even at lower concentrations and, above all, when ingested repeatedly . The lethal dose of aflatoxin B 1 in adults is 1 to 10 mg / kg body weight when ingested orally . In animal experiments with rats (lethal dose 7.2 mg / kg body weight), the carcinogenicity of a daily dose of 10 µg / kg body weight was clearly demonstrated. Aflatoxin B 1 is thus one of the most powerful carcinogenic compounds.

The carcinogenic effect of aflatoxins is based on the fact that they are oxidatively converted into a very reactive epoxide after being absorbed in hepatocytes (phase I of the biotransformation). This is done with the help of cytochrome P450 . The epoxide can be made soluble as glutathione- S conjugate (phase II of the biotransformation) and then excreted by appropriate transport systems (MRP2 transporter, ATP-dependent) (phase III of the biotransformation), but the epoxide can also penetrate the nucleus , there form adducts with the DNA and thus cause mutations or tumors .

The neoplasia occurs with oral use particularly prevalent in the liver and stomach. Since the mold spores also contain aflatoxins, inhaling the dusts when working with aflatoxin-containing products can lead to lung cancer. Therefore, maximum levels for aflatoxins have been set in certain foods since 1976.

In the 2008 food monitoring report, quantifiable amounts of aflatoxin B1 were found in 6 of 88 rice samples , and one sample exceeded the maximum permitted level.

Aflatoxins are thermally stable , ie they cannot be destroyed by heating (boiling, frying, etc.).

Occurrence

Molds such as Aspergillus flavus are found in soil, rotting vegetation, and hay and grain that is exposed to microbial spoilage. They attack organic substrates of all types when conditions favor their growth. Such growth-promoting conditions are e.g. B. high temperature and humidity like in tropical regions. However, the presence of Aspergillus flavus alone is not sufficient for the production of harmful levels of aflatoxins.

The aflatoxins that occur in (vegetable) foods are aflatoxins B 1 , B 2 , G 1 and G 2 . Aflatoxins M1 and M2 occur in milk.

Aspergillus flavus

Aspergillus flavus is common and widespread in nature. It is usually found when the growth of peanuts , poppy seeds or certain types of grain under poor (stressful) conditions, such as B. drought occurs, or the products are contaminated during harvest or storage. The fungus has been found on pistachios in a variety of cases. The load varies greatly depending on the country of origin and the harvesting method. Also, only 40 percent of the fungal strains examined produce aflatoxins.

Aspergillus parasiticus

A. parasiticus is commonly found in peanuts and is only found in certain regions. All of the fungal strains examined can produce B and G aflatoxins.

Other Aspergillus and Emericella species

Other types of mold that produce aflatoxins have been found. However, these are rarely to very rarely encountered. B and G aflatoxins are produced by A. nomius , A. toxicarius , A. parvisclerotigenus and A. bombycis . B-aflatoxins were also found in A. pseudotamarii , A. ochraceoroseus , A. rambelli as well as Emericella astellata and E. venezuelensis .

synthesis

Total synthesis of aflatoxin B2 (Tf = triflyl group )

Analytics

For reliable identification and quantification in food and other complex test items, chromatographic methods with fluorescence detection or the coupling of HPLC with mass spectrometry are used after appropriate sample preparation . The results of so-called rapid tests should always be checked using HPLC / MS methods in order to avoid misinterpretations with considerable health or economic consequences. Reference materials can be used to ensure the quality of the analytical methods used.

Maximum permissible values

The following limit values ​​apply in the European Union: 2 μg kg −1 for aflatoxin B1 and 4 μg kg −1 for the sum of the aflatoxins B1, B2, G1, G2 in various foods. There are various limit values ​​(also dependent on processing) between 2 and 12 μg kg −1 for aflatoxin B1 and between 4 and 15 μg kg −1 for the sum of aflatoxins B1, B2, G1, G2 in various spices and nuts , Oil seeds , dried fruits, corn and rice. Refined vegetable oils and their raw materials are excluded, as the aflatoxins must be removed during refining. Aflatoxin M1 is subject to a limit of 50 nanograms per liter (0.050 μg · L −1 ) raw milk , heat-treated milk and factory milk as well as 25 nanograms in baby food. Food for infants (and young children) may only contain 0.1 μg kg −1 aflatoxin B1.

There are numerous nationally different regulations on this.

Table. Tolerance level for aflatoxin B1 in international comparison
Country Maximum permitted amount [μg · kg −1 ] product
Canada 15th nuts
United Kingdom 20th Food
European Union 2 Nuts, dried fruits, cereals
Switzerland 8th Almonds, pistachios and apricot kernels
Argentina 0 Peanuts, corn and corn products
Brazil 15th Food
China 10 Rice and table oils
Czech Republic 5 Food
Hungary 5 Food
India 30th Food
Japan 10 Food
Nigeria 20th Food
Poland 0 Food
South Africa 5 Food
Zimbabwe 5 Food

Since aflatoxin is thermally stable , the food industry uses sodium hypochlorite or comparable processes to clean certain processing machines . The success of the cleaning process is then demonstrated by high-performance liquid chromatography with fluorescence detection.

Aflatoxins as biological warfare agents

Aflatoxins are suspected of being stored as warfare agents due to their comparatively simple production method and the low lethal dose. For example, between 1985 and 1991 around 2200 liters of aflatoxin were produced in Iraq as a warfare agent with which R-17 missiles were supposed to be equipped.

Contamination of food

Aflatoxins in harmful amounts are most commonly found in dry products such as pistachios , peanuts , hazelnuts , Brazil nuts , dried figs and spices .

Feed load

On March 1, 2013, up to 0.204 milligrams of aflatoxin B1 per kilogram of contaminated maize was found in Germany after 57 nanograms of aflatoxin M1 per kilogram of milk on a farm and the maize delivery from Serbia as a feed component had been determined. Forage from the maize delivery had been delivered to several thousand other farms in Lower Saxony and some farms in other federal states. In the previous months, increased aflatoxin levels in maize were reported from various European countries. In Serbia, a large part of the 2012 harvest was contaminated.

According to press reports, the affair of animal feed imports contaminated with mold will not result in stricter controls at the federal level. A similar case was documented in Ethiopia in June and November 2015.

Individual evidence

  1. ↑ Albert Gossauer: Structure and reactivity of biomolecules. Verlag Helvetica Chimica Acta, Zurich, 2006, ISBN 3-906390-29-2 , pp. 422-423.
  2. ↑ a b c d e J. C. Frisvad, U. Thrane, RA Samson, JI Pitt: Important mycotoxins and the fungi which produce them . In: Adv. Exp. Med. Biol. Band 571 , 2006, p. 3-31 , doi : 10.1007 / 0-387-28391-9_1 , PMID 16408591 .
  3. ↑ a b c Annual Consumer Protection Report 2000 . (PDF; 1.5 MB). Lower Saxony Ministry of Food, Agriculture and Forests.
  4. ↑ Georg Löffler, Petro E. Petrides: Biochemistry & Pathobiochemistry. 8th edition. Springer-Verlag, 2007, ISBN 978-3-540-32680-9 .
  5. ↑ Federal Office for Consumer Protection and Food Safety: Food Monitoring Report 2008 . P. 42.
  6. ↑ N. Arroyo-Manzanares, AM García-Campaña, L. Gámiz-Gracia: Multiclass mycotoxin analysis in Silybum marianum by ultra high performance liquid chromatography-tandem mass spectrometry using a procedure based on QuEChERS and dispersive liquid-liquid microextraction. In: J Chromatogr A. March 22, 2013, pp. 11-19. doi : 10.1016 / j.chroma.2013.01.072 . PMID 23415469 .
  7. ^ R. Salter, D. Douglas, M. Tess, B. Markovsky, SJ Saul: Interlaboratory study of the Charm ROSA Safe Level Aflatoxin M1 Quantitative lateral flow test for raw bovine milk. In: Journal of AOAC International . 89 (5), Sep-Oct 2006, pp. 1327-1334. PMID 17042183 .
  8. ↑ RD Joseph F. Ulberth, HP Van Egmond, H. Emons: aflatoxin M1 in milk powders: processing, homogeneity and stability testing of certified reference materials. In: Food Addit Contam. 22 (9), Sep 2005, pp. 864-874. PMID 16192073 .
  9. ↑ Regulation (EU) No. 165/2010 .
  10. ^ LL Charmley, HL Trenholm: Fact Sheet - Mycotoxins. ( Memento of May 7, 2010 on the Internet Archive ) Canadian Food Inspection Agency.
  11. ↑ Ordinance of the EDI on the maximum levels for contaminants In: admin.ch , accessed on February 12, 2020
  12. ↑ Hamed K. Abbas: Aflatoxin and food safety. 2005, p. 543ff.
  13. ↑ T. Vasek: Truth seeker with the father of all deceivers. In: The time. 40, 2002.
  14. ↑ Deutschlandfunk broadcast “Research News” on March 1, 2013, moderated by Ulrich Blumenthal .
  15. ↑ 2003/493 / EG: Commission decision of July 4, 2003 on the adoption of special provisions for the import of Brazil nuts in shells whose origin or origin is Brazil , accessed on February 25, 2015 .
  16. ↑ Lower Saxony Ministry of Food, Agriculture and Consumer Protection: Feed contamination with aflatoxin B 1 found (press release of March 1, 2013).
  17. ↑ Lower Saxony Ministry of Food, Agriculture and Consumer Protection: Aflatoxin B1 in fodder maize - current status .
  18. ↑ Federal Ministry of Food, Agriculture and Consumer Protection: Press release No. 73 of March 1st, 2013 Increased levels of aflatoxin in feed maize from Serbia ( Memento of December 20, 2015 in the Internet Archive ).
  19. ↑ Political News (January 25, 2013) Serbia: Aflatoxin in maize . In: Österreichische Ärztezeitung.
  20. ↑ Fungal feed: no controls at federal level. ( Memento of May 27, 2013 in the Internet Archive ) of April 5, 2013.
  21. ↑ Ethiopia: Milk Malaise (November 14, 2015) .

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