Aflatoxins: Invisible killer

Aflatoxins (AF) are part of a group of toxins called mycotoxins which are produced by moulds. These mycotoxins are secondary metabolites produced by several species of fungi (moulds) in the genera Aspergillus, Penicillium, and Fusarium, and are found in several kinds of food, especially cereals, nuts and derived products.

Aflatoxins are produced by different species of Aspergillus (mainly A. flavus, A. parasitcus, and A. nomius), a mould (fungus) which is especially found in areas with hot and humid climates. The moulds are naturally found in the air, soil, on insects and plants and grow on crops and grains and produce aflatoxins to contaminate these crops.

Generally, aflatoxin contamination can occur at both pre-and post-harvest stages of the agricultural chain.  Grains containing toxin-producing moulds can be difficult or impossible to recognise because it may not appear overly mouldy. Even when visibly mouldy, you cannot see aflatoxins in the grain with your naked eye.  Hence their effect on health unfortunately is seriously unnoticed in developing countries, including Ghana.  Exposure to aflatoxins by domestic animals and humans can only be detected and quantified through diagnostic laboratories.

Contamination

Aflatoxins may be present in foods such as treenuts, peanuts (groundnuts), corn/maize, rice, dried fruits, spices, raw vegetable oils, and cocoa beans with fungal contamination before and after harvest. In Ghana, the presence of aflatoxins has been detected in peanuts (groundnuts), maize, melon seeds (agushie), chili powder, corn meals, rice, tom brown, hausa koko, sorghum and groundnut paste.

Liver Cancers

Aflatoxin B1 (AFB1) has been recognised by the International Agency for Research on Cancers as a major risk factor for liver cancer which is a Class 1 carcinogen. When aflatoxins are ingested through food, the liver in its attempt to remove it from the body produces a carcinogenic form that binds to cellular molecules to form compounds that lead to gene mutation or cancer. 

Aflatoxins cause liver necrosis, liver tumours, reduced growth, depressed immune response and carcinogenesis. When one is exposed to very high levels of aflatoxins, it can be fatal. Chronic exposure to low levels can lead to liver cancer and cause suppression of the immune system. Also, the consumption of aflatoxin-contaminated food facilitates the development of liver cirrhosis in a person with hepatitis B. Usually aflatoxin B1 and hepatitis B infections commonly occur in areas with high rates of hepatocellular carcinoma (HCC).  Additionally, immunosuppression caused by the intake of aflatoxins is detrimental for an HIV positive person. This presupposes that consumption of food high in aflatoxins will not be good for a person with COVID-19.  

Childhood stunting

Aflatoxins are also responsible for childhood stunting with some linkage to kwashiorkor. It is estimated that around 30 per cent of all liver cancers worldwide could be related to aflatoxins exposure. In livestock, aflatoxins can cause weight loss and death. Milk, meat or eggs obtained from animals fed with contaminated feed may contain aflatoxins.

Aflatoxin contamination contributes to nutritional and economic losses in major commodities. Products prepared from contaminated raw materials do not meet international, national, regional regulations and standards governing agricultural or food trade and food safety.

Small scale farmers, who produce contaminated crops, do not meet food safety standards hence undermine local purchase programmes by development partners and, therefore, accessibility to other markets are also blocked.  Exporters are faced with rejects from border controls of importing countries when aflatoxin levels determined in prepackaged food or raw materials exceed allowable limits of these countries, especially the European Union.

Factors

Contamination by aflatoxins is becoming more or less inevitable in food commodities owing to the ever presence of the promoting factors involved in its production. Factors that easily promote the production of aflatoxins could be extrinsic: temperature; soil properties; relative humidity; mechanic injury on food commodity; insects and rodents attack; or intrinsic (pH, nutrient composition, moisture content / water activity). These factors have been shown not to work in isolation, thus, two or more factors have to be met before fungal growth and corresponding toxin synthesis can occur.   The most important factors that help predict the occurrence of aflatoxins in food include weather conditions (temperature and atmospheric humidity), agronomical practices (crop rotation and soil cultivation) and internal factors of the food chain (drying and storage conditions).

Based on numerous researches, aflatoxin formation has been found to occur in three basic stages in the food production chain. They are the cultivation stage with indicators being relative humidity, temperature, crop rotation, tillage practices and water activity of seeds.  Also transportation and storage stage, with indicators being water activity, relative humidity, ventilation, temperature, storage capacity and logistics. Lastly the processing stage, has indicators such as data quality, the fraction of grain used, the water activity of grains, implanted traceability and quality system.

Aflatoxin management strategies include a pipeline approach targeting predisposing factors to contamination. Pre-harvest strategies include host resistance, biological control and good agricultural practices, breeding and selection of aflatoxin resistant/stress tolerant crop varieties can help manage aflatoxins. Biological control using microbial antagonist to control disease is another form of management strategy with an example being Aflasafe. This Aflasafe is a biopesticide for aflatoxin mitigation which consist of sterile sorghum grains coated with four indigenous non-aflatoxin producing strains of A. flavus used on maize, sorghum & groundnut. Good Agricultural Practices (GAPs) is another pre-harvest management strategy and includes but not limited to crop rotation, pesticide application, soil amendment and moisture management.

During harvesting, one should harvest timely, dry produce rapidly and adequately, clean and sort grains and store properly with insect pest controls available in storage area.  Post-harvest strategies include good transportation practices and good storage practices. Some practices can also reduce the contamination levels and these include irradiation, use of plant extracts, nixtamalisation and ammoniation.

Best solutions

Using the integrated management approach to aflatoxin challenge is the best solution.

Buy seeds from a good source.

Plant and harvest on time.

 Apply the right inputs on time.

Apply Aflasafe.

Drying to safe moisture content is crucial.

Control insect in the field and in stores.

Sort grain before drying.

Clean and repair the stores.

Result of the change: improved crop. quality -  little to no contamination in grain.

Awareness creation/raising

It is important for both traders and consumers to buy clean and sound grains. Shrivelled, mouldy, broken, discoloured grains as well as grains that look spoilt should be removed from the lot before it is further processed  into powder, flour, paste or dough. Additionally, store products in well sealed and clean containers or bags in well ventilated and enclosed areas to prevent produce from getting moist.

The Ghana Standards Authority, with support from the Alliance for a green Revolution in Africa and partners is leading the National Aflatoxin Sensitisation and Management (NASAM) project to sensitise Ghanaians to the dangers of aflatoxins and how they can be managed.

The Author is the Head of Mycotoxin and Histamine Laboratory,

Food and Agriculture Department,

Ghana Standards Authority