Food Safety Challenges: The Case of Aflatoxin
Rose W. Njeru, Agro-Innovations International, Nairobi, Kenya
Aflatoxins are naturally occurring toxins (CODEX, 2013) that are poisonous to human beings and animals (Van Egmond et al., 2007). Poisoning occurs mainly through consumption of contaminated crop and animal products, but also through inhalation and absorption through the skin (Wagacha and Muthomi, 2008). The toxins are produced by some species of Aspergillus fungi (mould), which are widely distributed (Hedayati et al., 2004), and mainly found in cereals, oil seeds, spices and tree nuts. Under favourable high-temperature and -moisture conditions common in the tropics and sub-tropics (Thompson and Henke, 2000), the fungi produce at least 16 related toxins. There are four major ones (B1, B2, G1 and G2) with B1 being the most common and the most toxic (Hedayati et al., 2004). If animals eat feed contaminated with aflatoxin B1, it is broken down into a more potent toxin (M1), which contaminates animal products such as eggs, meat and milk (Kangethe and Langat, 2009, Demirhan and Yentür, 2014). Aflatoxins are resistant to heat and have been detected in pasteurized milk, cheese, peanut butter, cereal-based African traditional alcoholic beverages and infant foods (Dwivedi et al., 2004, Muthomi et al., 2012, Kengethe and Langat, 2009, Offifah and Adesiyun, 2007).
Aflatoxins are major challenges to the global food safety systems, health and nutrition and economies because they are produced during crop production, harvesting, transportation, storage and food processing (Murphy et al., 2006),. Exposure to high levels of aflatoxin leads to death from liver failure (Chao et al., 1991) and the most devastating case occurred in Kenya in 2004 (Lewis et al., 2005). Extended exposure to low levels (chronic poisoning) is suspected to cause liver cancer (MRC, 2001), reduced growth and kwashiorkor (protein malnutrition) in children (Okoth and Ohingo, 2004) and reduced ability to fight invasion by other disease-causing agents. Economic losses, particularly the financial burden on health care, disposal of contaminated food and feed, reduced productivity and barrier to trade, are enormous. The US Centers for Disease Control (CDC) have estimated that more than 4.5 billion people in developing countries are chronically exposed to toxins produced by various fungi, but primarily aflatoxins in their diets (CDC, 2004). These toxins are considered by US Food and Drug Administration and other regulatory agencies to be unavoidable contaminants of foods, hence the goal is to minimize contamination in foods and feeds through the application of standards and by enforcement of legislation. The maximum aflatoxin residue allowed in human foods is 4-30 μg/kg, depending on the country involved (FDA, 2004), except for milking. To minimize contamination, use of good agricultural and manufacturing practices is recommended, but the risk still exists if due care/attention is not paid.
|The largest case of aflatoxin poisoning documented worldwide occurred in Kenya in 2004 and resulted in 317 case-patients and 125 deaths, as reported in the local medical facilities. This was associated with consumption of home-grown maize stored under damp conditions (CDC, 2004, Lewis et al., 2005).|
Risk of aflatoxin contamination in the field & disease-resistant varieties
Aspergillus mould produces a tough resting structure (sclerotia), which allows it to survive in the soil, discarded products and in plant remains. In the absence of crop rotation, the fungus is able to infect maturing crops (Jaime-Garcia and Cotty, 2004, Olanya et al., 1997). Plants are most prone to Aspergillus attack when grown under sub-optimal conditions such as moisture stress, low soil fertility and infestation with pests and weeds (Holbrook et al., 2004, Wagacha and Muthomi, 2008). Timely harvesting and threshing reduces aflatoxin contamination (Rachaputi et al., 2002) but some farmers delay harvesting because of labour constraints. Further, if farmers plant varieties prone to Aspergillus attack and off-season rains fall during harvesting, the likelihood of contamination is high. It is critical that field contamination of crops is minimized because fungal growth and aflatoxin production continue with increasing vigour at postharvest and storage stages (Alakonya et al., 2009).
|Pre-harvest practices to minimize aflatoxin contamination entails use of good agricultural practices including: proper disposal of previous crop remains, crop rotation, growing tolerant crop variety (if available), timely planting, right plant density, good soil fertility, avoid moisture stress, timely pest and weed control and harvesting.|
One of the most promising long-term strategies in aflatoxin control is the development of resistant varieties. Sources of resistance to aflatoxin have been identified and introduced into public and private breeding programs (Wagacha and Muthomi, 2008). Also, two maize lines that are resistant to aflatoxin have been identified but few if any, commercial cultivars have adequate levels of resistance to aflatoxin producing fungi. In the USA, biological control measures that involve adding strains of nontoxigenic Aspergillus to the soil to outcompete the toxigenic Aspergillus strains are being used to reduce contamination on peanuts and maize (Dorner and Cole, 2002). However, these biological control products cannot be used in other countries because, to be effective, the nontoxigenic strain must originate from the soils where it will be used (Yin et al., 2008). In Africa, trials on biological control of aflatoxin using local strains are ongoing in Kenya and Nigeria, but at a more advanced stage in the latter where maize farmers have realized about 80% reduction in aflatoxin contamination (IITA, 2010). Further, commercialization of the product will require private-public partnership for mass production, marketing and distribution.
Product contamination during postharvest handling
The postharvest handling techniques used can contribute to contamination as crops are still at risk after harvest. For example, if they come into direct contact with soil beaten with sticks, cracks occur through which aflatoxin producing fungus enter. Additionally, most smallholder farmers rely on sun drying, exposing the product to weather fluctuations. Consequently, prolonged drying and failure to reach the desired moisture content (e.g. below 10% for peanuts and below 15.5% for maize) provides favourable conditions for fungal growth and aflatoxin build-up (Bhat and Visanthi, 2003). At the farm gate, physical removal of discoloured and mouldy grains can reduce contamination, but because the contaminated product may appear normal and without signs of fungal infection, the only accurate means to confirm aflatoxin contamination is to conduct a quality control test to determine the absence or presence of the toxin (Muthomi et al., 2012). However, low-cost rapid field-based test kits are not readily available to most small-scale producers. Also, most smallholder farmers lack accurate information on factors favouring aflatoxin build-up and its effect on human and animal health (Kangethe and Langat, 2009). As a result, contaminated grains are sometimes processed into alternative foods for human consumption or used to feed animals (Alakonya et al., 2009, Nikander et al., 1991). Furthermore, even well-dried products can be contaminated with spores floating in the atmosphere and pick up moisture if appropriate packaging materials and mode of transportation are not used. Thus, farmers, traders and processors need access to training and adequate processing and quality control equipment so that they can put the necessary measures in place to minimize fungal growth and aflatoxin build-up when handling food and feed (Bhat and Vasanthi, 2003).
|Postharvest handling practices to minimize aflatoxin contamination of product include: Avoid direct contact of product with the soil, use appropriate technology and minimize damage, fast drying to right moisture content, use appropriate packaging materials and mode of transport, pest control, store product in airtight bags in well-aerated stores, clean stores before loading new products.|
Risk of contamination during storage
Even in storage, aflatoxin build up can be a challenge. The fungi do not thrive under low-oxygen conditions (Wagacha and Muthomi, 2008), and contamination can be minimized by use of air-tight, moisture proof bags. These are in limited use in some African countries and they cost more than conventional bags. Pest infestation, especially insects, also cause an increase in moisture content and temperature, thereby creating favourable conditions for fungal growth (St. Leger et al., 2000). Thus, pest control is important. Further, some producers lack appropriate stores and bags containing produce can come into direct contact with the floor where temperature and condensation are relatively high. These conditions favour aflatoxin build-up. All grain and related products including animal feed should be stored under dry conditions. An effective strategy for aflatoxin control in peanuts exists, and is already in use in Haiti and is being promoted by CTA (Box 4). The control measure can be used in other countries, regions and also for other crops and countries.
|Aflatoxin control in groundnuts at (a) production stage involves: crop rotation, use of high quality seeds of early maturing, drought tolerant and disease resistant varieties, timely planting on fertile soils, proper control of pests and diseases (b) harvest/Post harvest stage: timely harvesting, avoid mechanical damage to pods, fast drying and threshing immediately using tarpaulins, ground nuts dried below 10% moisture, sorting to remove damaged, immature or rotten nuts, packaging in clean breathable bags and storing groundnuts in unshelled form for as long as possible in cool well aerated stores with pest control (dried neem leaves is effective for insect control), during marketing conduct moisture tests, use simple lateral flow dipstick tests for aflatoxin, ensure traceabilty of the product, created awareness about aflatoxin along the entire value chain and encourages two way flow of information (CTA Top innovation: Aflatoxin control).|
- Aflatoxin-producing fungus can contaminate the product at all stages of the value chain from the field, during harvesting, transportation, storage and food and feed processing.
- To address the challenge of aflatoxin contamination requires well-empowered farmers with knowledge and skills on how to produce products with reduced levels of aflatoxin, availability of cost-effective processing technology and quality control measures, well-informed traders and processors on how to minimize contamination during transportation and storage, strengthened surveillance for aflatoxin contamination and robust aflatoxin testing facilities.
- The use of good agricultural and manufacturing practices requires supportive institutional and policy environment. Thus, there is need to (a) have strong regulatory frameworks and enforce adherence to set standards, (b) support research to have the evidence on key trigger points along the commodity value chains to support interventions, develop fast, simple and affordable aflatoxin testing capability as well as improved and resistant varieties and alternative uses and safe methods of disposal of of contaminated produce, and(c) build the capacity of farmers and improve their access to adequate processing, aflatoxin testing and storage facilities.
Alakonya, A.E., Monda, E.O. and Ajanga, S. 2009. Fumonisin B1 and Aflatoxin B1 levels in Kenya maize. Journal of Plant Pathology, 91 (2), 459-464.
Bhat, R.V. and Vasanthi, S. 2003. Mycotoxin food safety risks in developing countries. Food Safety in Food Security and Food Trade. Vision 2020 for Food, Agriculture and Environment, Focus 10, Brief 3 of 17, pp. 1–2.
Centers for Disease Control and Prevention (CDC). 2004. Outbreak of aflatoxin poisoning - Eastern and Central provinces, Kenya, January–July, 2004
Chao, T.C., Maxwell, S.M. and Wong, S.Y. 1991. An outbreak of aflatoxicosis and boric acid poisoning in Malaysia: a clinicopathological study. Journal of Pathology, 164, 225-233.
CODEX, 2013. CODEX 193-1995. CODEX general standards for contaminants and toxins in food and feed.
Demirhan, B. and Yentür, G. 2014. Investigation of aflatoxin M1 levels in infant follow-on milks and infant formulas sold in the markets of Ankara, Turkey. Journal of Dairy Science, 97, 3328–3331.
Dorner, J.W. and Cole, R.J. 2002. Effect of application of nontoxigenic strain of Aspergillus flavus and A. parasiticus on subsequent aflatoxin contamination of peanuts in storage. Journal of Stored Products Research, 38, 329–339.
Dwivedi, P.D., Rastogi, S., Khanna, S.K. and Mkul, D. 2004. Detection of aflatoxin M1 in milk and infant milk products from Indian markets by ELISA. Food Control 15, 287–290.
Food and Drug Administration (FDA). 2004. Compliance guidance manual. http://www.cfsan.fda.gov.
Hedayati, M.T., Mohseni-Bandpi, A. and Moradi, S. 2004. A survey on the pathogenic fungi in soil samples of pitted plants from Sari hospitals, Iran. Journal of Hospital Infections, 58, 59–62.
Holbrook, C.C., Guo, B.Z., Wilson, D.M. and Kvien, C. 2004. Effect of drought tolerance on preharvest aflatoxin contamination in peanut. Proceedings of the 4th International Crop Science Congress Brisbane, Australia, 26 Sep–1 Oct 2004.
IITA. 2010. Making Kenyan maize safe from deadly aflatoxins. 05 June 2010. International Institute of Tropical Agriculture, Ibadan, Nigeria.
Jaime-Garcia, R. and Cotty, P.J. 2004. Aspergillus flavus in soils and corncobs in South Texas: Implications for management of aflatoxins in corn-cotton rotations. Plant Disease, 88, 1366–1371.
Lewis, L., Onsongo, M., Njapau, H., Schurz-Rogers, H., Luber, G., Kieszak, S. et al. The Kenya Aflatoxicosis Investigation Group. 2005. Aflatoxin contamination of commercial maize products during an outbreak of acute aflatoxicosis in Eastern and Central Kenya. Environmental Health Perspectives, 113, 1763–1767.
Medical Research Council (MRC). 2001. Aflatoxin in peanut butter. Science in Africa. http://www.scienceinafrica.com/health/aflatoxin-peanut-butter-mrc-policy-brief
Murphy, P.A., Hendrich, S. and Bryant, C.M. 2006. Food mycotoxins: an update. Journal of Food Science, 71(5), 51-65.
Muthomi, J.W., Mureithi, B.K., Chemining’wa, G.N., Gathumbi, J.K. and Mutit, E.W. 2012. Aspergillus species and Aflatoxin b1 in soil, maize grain and flour samples from semi-arid and humid regions of Kenya. International Journal of AgriScience, 2(1), 22-34.
Nikander, P., Seppala, T., Kilonzo, G.P., Hutten, P., Saarnen, L., Kilima, E. et al. 1991. Ingredients and contamination of traditional alcoholic bevarages in Tanzania. Transactions of Royal Society of Tropical Medicine and Hygiene, 85, 133–135.
Offifah, N. and Adesiyun, A. 2007 Occurrence of aflatoxin in peanuts, milk and animal feed in Trinidad. Journal of Food Protection, 70 (3), 771-775.
Olanya, O.M., Hoyos, G.M., Tiffany, L.H. and McGee, D.C. 1997. Waste corn as a point source of inoculum for Aspergillus flavus in corn agroecosystem. Plant Disease, 81, 576-581.
Okoth, S.A. and Ohingo, M. 2004. Dietary aflatoxin exposure and impaired growth in young children from Kisumu, Kenya: Cross sectional study. African Journal of Health Sciences, 11, 43-54.
Rachaputi, N.R., Wright, G.C. and Kroschi, S. 2002. Management practices to minimise pre-harvest aflatoxin contamination in Australian groundnuts. Austrian Journal of Experimental Agriculture, 42, 595–605.
St. Leger, R.J., Screen, S.E. and Shams-Pirzadeh, B. 2000. Lack of host specialization in Aspergillus flavus. Applied and Environmental Microbiology, 66, 320–324.
Thomson, C. and Henke, S.E. 2000. Effects of climate and type of storage container on aflatoxin production in corn and its associated risks to wildlife species. Journal of Wildlife Diseases, 36, 172–179.
Van Egmond, H.P., Ronald, C.S. and Marco, A. J. 2007. Regulations relating to mycotoxins in food. Perspectives in a global and European context. Analytical and Bioanalytical Chemistry, 389, 147-157.
Wagacha, J.M. and Muthomi, J.W. 2008. Mycotoxin problem in Africa: Current status, implications to food safety and health and possible management strategies. International Journal of Food Microbiology,124, 1-12.
Yin, Y., Yan, L., Jiang, J. and Ma, Z. 2008. Biological control of aflatoxin contamination of crops. Journal of Zhejiang University Science, 9 (10), 787-792.
Published by CTA, http://knowledge.cta.int/
Edited by J.A. Francis, CTA
Citation: CTA 2014. http://knowledge.cta.int/, “author” accessed on “date.”
Copyright CTA 2014. Articles and material published on Knowledge for Development http://knowledge.cta.int/ can be freely reproduced, provided that authors and source are fully acknowledged.
- Download PDF (278.47 kB)