The aflatoxins group mainly consists of aflatoxin B1; B2; G1; G2 and M1. Aflatoxins are produced by strains of Aspergillus, particularly A. flavus and A. parasiticus. Aflatoxin B1 is one of the most potent naturally occurring carcinogens1.
Main types of aflatoxins
Aflatoxins are named for their respective innate fluorescent properties2. Aflatoxin B1 and B2 exhibit a blue fluorescence while Aflatoxin G1 and G2 exhibit a green fluorescence. Aflatoxin B1 is considered the most toxic aflatoxin. This mycotoxin is metabolized in the liver, where it forms secondary toxic metabolites like the hydroxylated form aflatoxin M1.2, 3, 4, 5
- Aflatoxin B1 and B2 are mainly produced by A. flavus and A. parasiticus
- Aflatoxin G1 and G2 are primarily produced by A. parasiticus
- Aflatoxin M1 is the metabolized form of aflatoxin B1 in humans and animals
Production and occurrence
Production of aflatoxins is greater during hot and humid conditions (optimally with day temperatures around 32°C and night temperatures around 24°C).2, 5, 6 Aflatoxins often develop during storage, though contamination of food and feed material can also occur in the field e.g. on crop parts damaged by pests or drought. Inadequately dried material or high humidity contribute to the production of aflatoxins in storage.2, 5, 7
The fungi that produce aflatoxins spread by spores (microconidia) through rain splash, wind and insects. Spores germinate and the fungi can penetrate plant material often facilitated by pest or other damage.2 Grains that are stored with high moisture content (e.g. >14%), at high temperatures (>20°C) and with damage can potentially be contaminated (Table 1).2 Because individually damaged grains can have a high aflatoxin content , there can be a very heterogeneous distribution of aflatoxins and sampling needs to be conducted carefully to avoid missing a contamination problem.
Table 1. Conditions favoring Aspergillus flavus growth
Aflatoxins are very stable compounds and resist several food processing techniques like roasting, extrusion, baking and cooking, hence they represent a severe risk for humans and animals.5, 6, 7, 8
A ten-year survey of more than 74,000 samples reveals that aflatoxin B1 is most prevalent in samples gained from South Asia (82.2%), Sub-Saharan Africa (76%), Southeast Asia (57.4%) and Southern Europe (28.9%). The most affected crops analyzed in the study were maize and rice with a prevalence of 24% and 31% and a median concentration of 4 ppb and 5 ppb, respectively.9 Also foodstuff including dried fruits (figs), coffee, spices and peanuts are regularly contaminated with Aflatoxins.
Toxicity and effects
Aflatoxin B1 is considered the most toxic aflatoxin. The main target organ for aflatoxins is the liver where it is metabolized and forms secondary toxic metabolites like the hydroxylated form, aflatoxin M1.2, 3, 4, 5 This mycotoxin is excreted in the urine and in the milk. Studies have shown that aflatoxin M1 can be detected in milk just 12-24 hours after exposure.2, 5 Additionally, a consistent aflatoxin M1 presence in milk occurs after 3-6 days of continuous consumption of aflatoxin B1 contaminated feed.2, 5, 8
Aflatoxins are genotoxic compounds and target several organs like the liver, kidneys, reproductive and immune systems.2, 5, 6, 7 They are potent carcinogens for humans and all animal species investigated, and young animals have been shown to be more susceptible than mature ones.10 These mycotoxins were included in the International Agency for Research on Cancer’s (IARC) group 1 (substances that are highly carcinogenic for humans) in 2002.5, 8 Aflatoxins are the only mycotoxins that are strictly regulated in markets like the EU and USA.3, 4, 8
Typical symptoms caused by aflatoxins:
- Fatty liver
- Liver cancer
Other aflatoxin related symptoms 5, 6, 7, 8:
- Encephalopathy with fatty degeneration of viscera
- Pulmonary interstitial fibrosis
Aflatoxins in corn (maize)
In 1920, Aspergillus flavus was reported to cause an ear mold of corn, but it took up to the 1960s until the fungus could be recognized as toxigenic when it was shown to be associated with Turkey X disease.2
The fungus can be identified by the yellow-green or grey-green spore masses visible at sites of kernel damage. Heavily damaged kernels that are cracked open may fluoresce bright greenish-yellow (BGYF) and provide a “presumptive” indication of the presence of aflatoxin. Individual kernels of corn may contain as many as 400,000 ppb (μg/kg) of aflatoxin. Therefore, sampling is very important in analysis for levels of contamination in bulk grain lots,2 as aflatoxin contamination can result in dramatic economic losses.11
Aflatoxin M1 in milk
Aflatoxin M1 is a hydroxylated metabolite of aflatoxin B1, which was first found present in milk and can be detected in urine as well. It is not produced directly by Aspergillus flavus or any other aflatoxin-producing fungus, therefore, it is not considered as a contaminant of feed grains but of milk and milk products. Aflatoxin M1 is very stable at high temperatures.
The most important step in the process of testing for aflatoxins is proper sampling, as the uneven distribution of aflatoxins in grains often results in high sampling error. For aflatoxin testing, the lab sample must be of at least 10 kg and the retention sample of 10 kg, resulting in a total quantity of 20 kg as recommended by ISO 24333: 2009 and European Commission Regulation (EC) No 401/2006.12
Aflatoxins are primarily considered field mycotoxins. Different strategies can be used to reduce the levels and occurrence of aflatoxins in agricultural products.
These strategies are divided into two methods:
- Prevention: management systems to reduce crop contamination in the field and during storage
- Detoxification: degradation or removal of aflatoxins from crops, adsorption in the gastrointestinal tract
Fungal growth and mycotoxin production can occur both in the field and during storage. Therefore, pre- and post-harvest measures are essential to prevent fungal colonization and mycotoxin occurrence.
A sustainable method to prevent aflatoxin formation in the field is the use of biocontrol using non-aflatoxigenic mold strains which can compete with aflatoxigenic strains and colonize fields where crops susceptible to aflatoxin contamination are cultivated.13
Aflatoxin contamination also can be minimized with proper management including:
- Thorough grain cleaning
- Proper combine adjustment to reduce kernel damage
- Matching drying capacity to wet corn holding capacity
- Proper drying
- Removal of fines and broken kernels
- Proper grain cooling after drying
- Correct storage practices
- Sanitation of equipment for harvesting including the removal of all broken corn, dust and foreign material that can provide a source of contamination
The prevention of aflatoxin formation in the field and during storage is the first step to reduce the risk of aflatoxin contamination. Detoxification strategies aim to deactivate, destroy or remove the toxin and fungal spores, while retaining the nutrient value and acceptability of the feed by the animal. Physical and chemical processes can be effective against aflatoxins but can be time consuming and costly. Biological methods include the use of adsorbant materials to prevent aflatoxicosis. These compounds bind aflatoxins in the gastrointestinal tract, thus reducing the amount of aflatoxins entering the bloodstream.
Only Bentonite with an aflatoxin B1-binding capacity above 90% is authorized by the European commission as a substance for reduction of the contamination of feed aflatoxin B1 for ruminants, poultry and pigs (European Commission Regulation (EC) No 1060/2013).14
- Krska R., Nährer K., Richard J. L., Rodrigues I., Schuhmacher R., Slate A. B., Whitaker T. B., (2012). Guide to Mycotoxins featuring Mycotoxin Risk Management in Animal Production. BIOMIN edition 2012
- COMMISSION REGULATION (EC) No 1881/2006 of 19 December 2006 setting maximum levels for certain contaminants in foodstuffs. Official Journal of the European Union. L 364/5
- FDA (2019): Sec. 683.100 Action Levels for Aflatoxins in Animal Food, Compliance Policy Guide.
http://www.fda.gov/ICECI/ComplianceManuals/CompliancePolicyGuidanceManual/ucm074703.htm; accessed: 13.08.2021
- Marin S., Ramos A.J., Cano-Sancho G., Sanchis V., (2013). Mycotoxins: Occurrence, toxicology, and exposure assessment. Food and Chemical Toxicology (60) 218-237
- Savard M.E., (2008). Mycotoxins- an introduction. Stewart Postharvest Review 2008 6:1
- Richard J.L., (2007). Some major mycotoxins and their mycotoxicoses - an overview. International Journal of Food Microbiology (119) 3-10
- Cardona T.D., Ilangantileke S.G., Noomhorn A. FAO Food and Agriculture Organization. http://www.fao.org/docrep/X5036E/x5036E1e.htm; accessed: 13.08.2021
- Gruber-Dorninger, C., Jenkins, T., & Schatzmayr, G. (2019). Global mycotoxin occurrence in feed: A ten-year survey. Toxins, 11(7), 375
- CAST (2003): Mycotoxins Risks in Plant, Animal, and Human Systems. Council for Agricultural Science and Technology, Ames, Iowa, USA
- Focker, M., van der Fels-Klerx, H.J. & Oude Lansink, A.G.J.M. (2021). Financial losses for Dutch stakeholders during the 2013 aflatoxin incident in Maize in Europe. Mycotoxin Res 37, 193–204
- COMMISSION REGULATION (EC) No 401/2006 of 23 February 2006 laying down the methods of sampling and analysis for the official control of the levels of mycotoxins in foodstuff. Official Journal of the European Union. L 70/12
- USEPA (2003). Biopesticide registration action document Aspergillus flavus AF36. https://www3.epa.gov/pesticides/chem_search/reg_actions/registration/decision_PC-006456_3-Jul-03.pdf; accessed: 13.08.2021
- COMMISSION IMPLEMENTING REGULATION (EU) No 1060/2013 of 29 October 2013 concerning the authorisation of bentonite as a feed additive for all animal species. Official Journal of the European Union. L 289/3