Aflatoxin

ABOUT AFLATOXINS

Aflatoxins are naturally-occurring toxin produced mainly by the fungi Aspergillus flavus and Aspergillus parasiticus. Ghana and many African countries have a tropical climate with an average temperature ranging from 24-30˚C, which is optimum for the growth of Aspergillus flavus and Aspergillus parasiticus in food and feed. Aflatoxins are likely to be produced when crops are exposed to extreme conditions such as high temperatures, drought, high moisture, high oxygen concentration, and insect infestation. Aflatoxin production can occur during the pre-harvest and post-harvest periods. High levels of moisture and temperature conditions create a suitable environment for the rapid growth of moulds, which in turn metabolize and produce aflatoxins. Furthermore, physical damage to crops during weeding, harvesting, drying, transportation, storage and marketing can cause decay that enhances the production of aflatoxins.

In most cases, the Aspergillus moulds are visible but aflatoxins that they produce are not visible.  In some situations, aflatoxins can be present in foods that are not visibly mouldy. Aflatoxins can be quantitatively detected through laboratory analysis. Rapid test kits and UV lights can be used to qualitatively detect the presence of aflatoxins in food and feed.

What food products are mostly affected by aflatoxins?

Aspergillus moulds can infest a wide variety of food products and produce aflatoxins. In Ghana, aflatoxins have been mostly detected maize and groundnuts, which are major staple foods. Aflatoxins have also been found in melon seeds (agushie), powdered pepper, corn flour, corn dough, rice, sorghum, millet, groundnut paste, khebab powder and some spices.  Animal and fish products can also be contaminated with aflatoxin if livestock, poultry and fish (cultured fish) are given feed that is contaminated with aflatoxins.

How do human and animals get exposed to aflatoxins?

Human and animals get exposed to aflatoxins by two major routes:

1. By direct ingestion of aflatoxin-contaminated foods or ingestion of aflatoxins carried over from feed into animal products such as milk and milk products, meats and eggs.
2. By inhalation of dust particles of aflatoxins especially aflatoxin B1 in contaminated foods in industries and factories.

It is possible for aflatoxins to cross the placenta and get transported to the foetus and unborn child where they can cause detrimental effects. Infants can get aflatoxin M1 from breast milk of mothers who were exposed to aflatoxins.

What are the health effects of aflatoxins?

Exposure to very high levels of aflatoxin results in acute health effects such as aflatoxicosis, which can cause symptoms such as haemorrhage, acute liver damage, vomiting, abdominal pains, coma, and death in severe cases.

Aflatoxins are class 1 carcinogens hence chronic exposure to low levels of the toxins causes liver cancer, liver cirrhosis and impairment of liver function. The liver performs important functions such as detoxifying and eliminating many toxins from the body hence its malfunctioning can lead to devastating health consequences.

When contaminated food is ingested, the aflatoxins are distributed in the blood to different tissues and to the liver where it is metabolised into both harmless and harmful products.  In the liver of humans and susceptible animals, aflatoxins especially aflatoxin B1 are metabolized by certain types of enzymes to a reactive form (aflatoxin-8,9-epoxide) that binds to DNA and to albumin in the blood serum, forming adducts and hence causing DNA damage. Aflatoxin B1 also binds directly to DNA and causes structural DNA alterations that lead to gene mutations. The binding of aflatoxin B1 to DNA at the guanine base in liver cells corrupt the genetic code that regulates cell growth, thereby leading to formation of cancerous tumours. 

Chronic exposure to low levels of aflatoxins can also result in immune suppression, increased susceptibility to infections; growth retardation and stunting in Children. In animals, chronic exposure to aflatoxins can lead to decreased protein synthesis, delayed recovery from protein-energy malnutrition such as kwashiorkor, reduced bioavailability of liver and serum vitamin A, zinc and selenium.

What are the measures for controlling aflatoxins in food?

The farm level strategies for controlling aflatoxins are:

• Development and production of aflatoxin-resistant varieties
• Use of biological control products such as Aflasafe GH02 to eliminate the aflatoxin-producing moulds
• Adopting good agricultural practices such as crop rotation, planting drought and disease-resistant seeds, planting treated and healthy seeds, appropriate pesticide application, moisture management, disease and pest control, irrigation, timely application of soil nutrients (fertilisers), and timely harvesting.

Post-harvest strategies for controlling aflatoxins are:

• Rapid and adequate drying after harvesting crops:
• Cleaning and sorting mouldy, discoloured and damaged grains
• Proper storage under good conditions to provide protection against water, insects and excessive heat, which are factors that promote mould growth and aflatoxin production.
• Pest control
• Inactivation or detoxification using heat treatment, irradiation, chemical treatment, nixtamalisation and use of extracts from plant such as cloves, garlic and onion, cinnamon and other herbs including thyme, star anise seeds, and black and white pepper to inhibit fungal growth.