The effect of storage time on the levels of aflatoxins in stored legumes and assessment of good agricultural practices of smallholder farmers in Shamva and Makoni districts, Zimbabwe

Abstract

Legumes are an important source of food in developing countries and are highly prone to aflatoxin contamination. Significant health risks associated with aflatoxins in humans include liver cancer, teratogenicity, weakened immune system and stunted growth in infants. . The effect of storage time on the levels of aflatoxins in groundnuts, cowpeas, beans and bambara nuts produced by smallholder farmers in Makoni and Shamva districts of Zimbabwe were investigated for one storage season from June 2015 to April 2016. Pre and postharvest management practices that minimize aflatoxin contamination in legumes were assessed through knowledge, attitudes and practice survey. Of the 382 farmers interviewed, 64.1% had no information on aflatoxins and the health risks associated with consumption of food contaminated with aflatoxins. Observed management practices that reduced aflatoxin contamination in the legumes included sorting of legumes with 89.2% of the farmers removing mouldy and discoloured grains prior to storage, while 42% of farmers dried legumes on a plastic spread over the ground and 59.3% of the farmers were hand shelling the legumes to minimize cracking of seeds. From the odds ratio test, implementation of good pre and postharvest management practices was observed to reduce the levels of aflatoxins in legumes, leading to reduced dietary exposure of humans to aflatoxins. The levels of aflatoxins were determined using high performance liquid chromatography with a fluorescence detector after extraction and immunoaffinity clean up. Aflatoxins were detected in groundnuts, cowpeas, beans and bambara nuts during storage, with groundnuts having the greatest accumulation from 12.5% in June 2015 to 73.7% by April 2016. The levels of aflatoxinB1 increased from 6.2 μg/Kg to 20.52 μg/Kg and from 4.82 μg/Kg to 12.22 μg/Kg for groundnuts and cowpeas respectively during six months of storage. The levels of aflatoxins exceeded the maximum tolerable limit of 5 μg/Kg allowed in food by the government of Zimbabwe. Hence smallholder farmers in Makoni and Shamva districts are exposed to aflatoxins through consumption of contaminated legumes. From the current study, the levels of aflatoxins in legumes increased with increase in storage time and the farmer’s knowledge and practices were found to influence the contamination levels of aflatoxins in legumes. Therefore, farmers need to adopt proper storage facilities and good agricultural practices to reduce contamination of stored legumes by aflatoxins.