POST-HARVEST INCIDENCE OF AFLATOXINS AND FUMONISINS IN MAIZE AND ITS RELATIONSHIP TO CLIMATIC CONDITIONS IN MALAWI

Abstract

This study provided an assessment of incidence of aflatoxins and fumonisins contamination of maize after harvest under different agro-environmental conditions in Malawi and its relationship with climatic conditions. The maize samples for this study were from the 2015/16 growing season. A total of one thousand two hundred and ninety four (1294) samples of maize for human consumption were collected from rural farmers’ households and rural markets, providing a wide geographical coverage of Extension Planning Areas (EPAs) in Malawi’s four agro-ecological zones. A questionnaire was used to establish farmers’ knowledge on moulds, fumonisins and aflatoxins, processing and consumption patterns. Reveal Q+ kits were used for quantitation of total aflatoxins and fumonisins. Dietary intake of aflatoxins and fumonisins was estimated using procedures established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA). Data show most maize samples (> 75%) were widely contaminated with aflatoxins across Malawi’s agro-ecological zones. On average, fumonisins were detected in 45% of the samples, and co-occurred with aflatoxins in 38.64% of all maize samples. Maize samples collected from the Lower Shire agro-ecological zone (median 20.8 μg/kg) had relatively higher levels of aflatoxins (p < 0.05) than maize samples from the other agro-ecological zones (median: 3.0 μg/kg). Additionally, the majority (75%) of the positive samples from the Lower Shire agro-ecological zone had aflatoxin levels exceeding the EU regulatory limit (4 μg/kg), whereas 25%, 37% and 39% of positive samples exceeded the EU limit in the mid-elevation, lakeshore, upper and middle Shire and highlands agro-ecological zone, respectively. The Lower Shire agro-ecological zone is characterised by high mean monthly temperatures throughout the year and erratic rainfall. Therefore, the results of this study show highest aflatoxin counts in areas with the highest annual mean temperature, supporting the idea that meteorological conditions are the key factors of fungal colonization and mycotoxin production. In contrast to total aflatoxins, levels of total fumonisins in maize did not show a broad variation across the four agro-ecological zones. In general, almost all positive samples from across all agro-ecological zone exceeded the EU regulatory limit for fumonisins in maize products for infants of 0.2 mg/kg but fell short of the regulatory limit for adults of 4 mg/kg, but without discernible differences across the agro-ecological zones. For fumonisins, estimates of daily dietary intake exceeded the JECFA’s provisional maximum tolerable daily intake (PMTDI) of 2.0 μg/kg body weight (bw)/day in 40.4%, 50%, 38.6% and 35.2% (median of EPA values) of all samples collected from the highlands, mid-elevation, lakeshore and Lower Shire agro-ecological zones, respectively. In addition, the estimated daily intake of fumonisin exceeded the PMTDI in majority of the fumonisin positive samples, across all agro-ecological zones. Therefore, from a risk assessment perspective, the results of this study may offer a communication tool for stakeholders, including policy makers, to highlight the need for education and awareness for improved mycotoxin risk management in Malawi and possibly the Southern African region.