Scientists recommend best practice for minimizing aflatoxin contamination of maize
IITA researchers, working with scientists from other agricultural institutions, have come up with a pre-harvest practice for minimizing aflatoxin contamination of maize. The practice was developed and outlined in a study in Kenya, which was carried out to document the rate at which aflatoxin contaminates physiologically mature maize in the field.
Aflatoxins are secondary metabolites produced by Aspergillus flavus (A. flavus) and Aspergillus parasiticus fungi that are abundant in many tropical soils where maize (Zea mays L.) is grown. This is a serious problem affecting the short and long-term health of humans and animals, trade, and export markets of maize-based products. When consumed in low dosages over prolonged periods, aflatoxins may cause liver cancer, suppress immune systems, increase the occurrence and severity of infectious diseases, and lead to poor nutrient absorption and retarded child growth and development by contributing to malnutrition.
Maize, the main crop in Kenya, is most vulnerable to infection by A. flavus and contamination by aflatoxin. Aflatoxin contamination of maize grain has been a major issue in Kenya, where average per capita consumption is 400 g of maize/day. More than 75% of maize in Kenya is produced by smallholder farmers and mostly for their own consumption, while the surplus is informally traded. As a result, aflatoxin contamination of homegrown maize presents a significant threat to the health of rural and urban consumers, who are dependent on maize as their staple crop.
Kenya has witnessed periodic incidences of acute aflatoxin poisoning, dating back to 1981, because of consumption of aflatoxin-contaminated maize. Multiple aflatoxicosis outbreaks have been documented since 2004, resulting in nearly 500 acute illnesses and 200 deaths.
However, a study was carried out in Eastern Kenya, a high aflatoxin-risk region with reported cases of acute aflatoxin poisoning, and in South Western Kenya, which is considered a low-risk region with no published reports of aflatoxin poisoning. About 789 maize samples were collected from smallholder farmers’ fields while the crop was still in the field. The samples were collected from Embu, Makueni, and Machakos of Eastern Kenya and Homabay, Migori, and Kisii of South Western Kenya. Also, 10 farmers were randomly selected from each village, with a distance of about 5 km between the villages and farms to obtain a representative sample.
A 1-kilogram sample was taken per farm and transported to the laboratory for aflatoxin extraction and analysis. For each sample, the farmer’s name, village, location (GPS coordinates), and name of maize variety were recorded. Results revealed significant levels of pre-harvest aflatoxin contamination of maize in both regions, although higher in Eastern Kenya.
The presence of many pre-harvest maize samples contaminated by aflatoxin in both regions revealed the importance of developing strategies for minimizing aflatoxin contamination while the crop is still in the field. In line with this, technologies such as the use of resistant maize varieties, good crop husbandry to minimize damage from insects and diseases, and proper fertilization schemes can go a long way to minimize A. flavus infection and subsequent aflatoxin contamination.
In addition, adopting technologies that minimize stress by combining heat and drought tolerant maize lines with high levels of resistance to A. flavus and aflatoxin contamination should be emphasized. However, biological control using atoxigenic strains of A. flavus to prevent infection by toxigenic strains was found to consistently reduce aflatoxin contamination by 80% and should be promoted to become an integral part of pre-harvest aflatoxin control measures.
The full article is available here: https://doi.org/10.1016/j.foodcont.2018.08.032
Mahuku G., Nzioki S.H., Mutegi C., Kanampiu F., Narrod C., Makumbi D. Pre-harvest management is a critical practice for minimizing aflatoxin contamination of maize. Journal of Food Control, 2019: 219-226.