Aflatoxins

Diet supplements oat grain on canvas closeup
Oats for lowering cholesterol. Copyright: morisfoto / 123RF Stock Photo

Aflatoxins (AFs) are potent mycotoxins produced by mostly several types of aspergillus moulds. The main species are Aspergillus flavus, Aspergillus parasiticus and Aspergillus nomius. These fungal metabolites induce a range of detrimental problems in humans when they are ingested:- mutagenic, teratogenic and carcinogenic effects ( Rustom, 1997). The overriding issue is they are strongly associated with liver cancer i.e. are hepatocarcinogenic. If the levels are too high then liver cirrhosis can occur soon followed by death (CDC, 2004).

Aflatoxins can contaminate many different feed and food crops, including peanuts and groundnuts, corn (maize), cottonseed, pistachios and other tree nuts, spices etc. There is widespread contamination in hot and humid regions of the world (Murphy et al., 2006; Doster et al., 2014; Kachapulula et al., 2017).

There are four major aflatoxins B1, B2, G1 and G2 and the first mentioned, B1 is probably the most dangerous.

Regulations And Legislation

The regulatory limits for aflatoxins in all feed- and foodstuffs for consumption is now tightly regulated. It follows years of examination on the safety and the risks posed. In the USA for example, the level of total aflatoxin in human food must be below 20 μg/kg total. Not all countries have legislation for setting the maximum limit for aflatoxin content. India is a good example where zearalenone for example does not have a maximum permissable level.

Commercial Considerations

The presence of aflatoxins of any sort can be especially damaging to growers because it means whole batches must be dispensed with. If the regulations were not enforced or even existing, then contamination with these toxic metabolites proves to be a severe health risk. It is known that certain products from various countries are not even considered because of poor supply chain management. Even if the concentration levels are sub-lethal then there is an association with stunted development in young people and animals ingesting these toxins (Khlanwiset et al., 2011), various forms of cancer and with immune suppression (Turner et al., 2003; Liu and Wu, 2010).

The Aflatoxin Producing Moulds

Aspergillus flavus is very often implicated in the contamination of crop produced foods with aflatoxins. The species is divided into two major morphotypes. These are called the L and S strains. The S strains produce large amounts of sclerotia and few conidia. The L strain isolate produces sparse levels of sclerotia but many conidia. The strain to look out for is the S type because high levels of aflatoxins are always produced. The L type produces variable levels (Probst et al., 2010).

Aflatoxin often starts being produced in crops well before any harvesting. Crop infection often occurs when crops are facilitated by plant stresses and strains such as physical damage by insects and drought stresses. Higher temperature levels than a plant is normally used to should also be considered (Cotty et al., 2008). Levels of contamination rise as crops mature. The conidia of Aspergillus are air-borne and extremely common. New infections occur during post-harvest stages which complicates contamination further (Cotty et al., 1994; Marin et al., 2009).

Aflatoxin B1

Aflatoxin B1 (AFB1) is the most toxic to mammals and induces cell injury, free radical liberation and lipid peroxidation (IARC, 2002). AFB1 is metabolised by the liver through the cytochrome P450 enzyme system to generate the major carcinogenic metabolite AFB1-8,9-epoxide or other less mutagenic forms (Biehl and Buck, 1987, Murphy et al., 2006).

References

Biehl, M. L., & Buck, W. B. (1987). Chemical contaminants: Their metabolism and their residues. Journal of Food Protection, 50, pp. 1058–1073.

CDC, (2004) Outbreak of aflatoxin poisoning-eastern and central provinces, Kenya, January–July 2004. Morb. Mortal. Weekly Rep. 53, pp. 790–793.

Cotty, P.J., Probst, C., Jaime-Garcia, R. (2008) Etiology and management of aflatoxin

contamination. In: Leslie, J.F., Bandyopadhyay, R., Visconti, A. (Eds.), Mycotoxins:

Detection Methods, Management, Public Health and Agricultural Trade. CAB International, Oxfordshire, UK, pp. 287–299.

Cramer, B., Bretz, M. & Humpf, H.U. (2007). Stable isotope dilution analysis of the Fusarium mycotoxin zearalenone. Journal of Agricultural and Food Chemistry, 55, pp. 8353–8358

Doster, M.A., Cotty, P.J., Michailides, T.J. (2014) Evaluation of the atoxigenic Aspergillus flavus strain AF36 in pistachio orchards. Plant Dis. 98, pp.  948–956

Ehrlich, K.C., Chang, P.K., Yu, J., Cotty, P.J., (2004) Aflatoxin biosynthesis Murphy, P. A., Hendrich, S., Landgren, C., & Bryant, C. M. (2006). Food mycotoxins: An update. Journal of Food Science, 71, R51–R65.

International Agency for Research on Cancer. (2002) Traditional herbal medicines, some mycotoxins, naphthalene and styrene. In: IARC Monograph on the Evaluation of Carcinogenic Risk of Chemicals to Humans. 82. 

Liu, Y., Wu, F., 2010. Global burden of aflatoxin-induced hepatocellular carcinoma: a risk assessment. Environ. Health Perspect. 118, pp. 818–824.

Marín, S., Colom, C., Sanchis, V., Ramos, A.J., (2009) Modelling of growth of aflatoxigenic A. flavus isolates from red chilli powder as a function of water availability. Int. J. Food Microbiol. 128, pp. 491–496.

Kachapulula, P.W., Akello, J., Bandyopadhyay, R., Cotty, P.J., (2017) Aflatoxin contamination of groundnut and maize in Zambia: Observed and potential concentrations. J. Appl. Microbiol. 122, pp. 1471–1482.

Probst, C., Schulthess, F., Cotty, P.J., (2010) Impact of Aspergillus section Flavi community structure on the development of lethal levels of aflatoxins in Kenyan maize (Zea mays). J. Appl. Microbiol. 108, pp. 600–610.

Robens, J., Cardwell, K., (2003) The costs of mycotoxin management to the USA: management of aflatoxins in the United States. J. Toxicol. Toxin Rev. 22, pp.  139–152.

Rustom, I. Y. S. (1997). Aflatoxin in food and feed: occurrence, legislation, and inactivation by physical methods. Food Chemistry, 59, 57–67

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