Effectiveness of hermetic storage vessels in reducing aflatoxin B1 and fumonisin B1 in maize grain from Shamva and Makoni districts of Zimbabwe

Abstract

Maize, the major staple food in Zimbabwe is susceptible to infection with fungi and contamination with mycotoxins. Contamination of maize with mycotoxins including aflatoxins and fumonisins is of major human health concern. Practices that minimise contamination of maize with mycotoxins should be put in practice in order to prevent exposure of humans to mycotoxins. The current study was carried out in Shamva and Makoni districts from which 12 wards were purposively selected. In each ward, two villages were randomly selected from which households that produce and rely on maize as a staple food were recruited. A total of 448 households were recruited and randomly placed into three forms of treatment: recipients of hermetic metal silos, recipients of hermetic super bags and the control that stored maize in conventional storages namely polypropylene bags and traditional granaries. Maize that was being consumed in Shamva and Makoni before introduction of hermetic storage technology was collected in order to determine the current levels of aflatoxin B1 (AFB1) and fumonisin B1 (FB1) and current levels of human exposure to AFB1 and FB1 through consumption of maize. Maize produced during 2014/2015 cropping season was collected at harvest in order to determine levels of AFB1 and FB1 before grain was loaded into storage vessels. Factors that influenced levels of AFB1 and FB1 in maize before storage were determined. Maize that was produced during 2014/2015 cropping season was loaded into hermetic metal silos, hermetic super bags and conventional storage vessels between June and July 2015 and samples were collected in October 2015, January 2016 and April 2016 in order to determine and compare the levels of AFB1 and FB1 in maize. Aflatoxin B1 was determined using high performance liquid chramotography with post-column derivatisation and fluorescence detection whilst FB1 was determined using direct competitive ELISA. Deterministic approach was used to estimate levels of exposure of humans to AFB1 and FB1 through consumption of maize. One way analysis of varience with least significant difference post test was used to compare levels of FB1 in maize collected from different storage facilities. Fumonisin B1 was found in all maize that was being consumed in Shamva and Makoni before introduction of hermetic storage technology at mean concentrations of 265.11 and 331.90 μg/kg respectively. The levels of exposure to FB1 in populations of Shamva and Makoni exceeded 2 μg/kg body weight/day, the limit set by the World Health Organisation. Method of drying maize influenced levels of FB1 in maize and drying maize on the ground lead to high levels of FB1. Variety of maize influenced levels of FB1 in maize and the highest levels of FB1 were detected in SIRDA 113 variety of maize. Crop rotation influenced levels of FB1 in maize and cultivating maize in fields where maize and groundnuts were cultivated together in the previous cropping season lead to high levels of FB1 in maize. The application of organic or inorganic fertilisers in the fields of maize had no effect on levels of contamination of maize with FB1. Levels of FB1 increased with duration of storage of maize in hermetic and conventional storage vessels. Levels of FB1 in maize that was stored in hermetic storage vessels increased in a similar manner to levels of FB1 in maize that was stored in conventional storage vessels. Households that were consuming maize stored in hermetic and conventional storage vessels were exposed to levels of FB1 above 2 μg/kg body weight/day. Before introduction of hermetic storage technology, AFB1 was detected in 21.7% (N=166) of maize at mean concentration of 4.22±4.18 μg/kg in Shamva and 19.8% (N=222) of maize at mean concentration of 3.61±2.12 μg/kg in Makoni. Levels of exposure to AFB1 in households that were consuming maize that contained AFB1 exceeded 0.017 ng/kg body weight/day, reported to be of human health concern. Aflatoxin B1 was detected in 0.67% (N=448) of maize that was collected before storage at a mean concentration of 5.43 μg/kg. Proportion of maize that contained AFB1 in hermetic and conventional storage vessels increased with duration of storage. Hermetic metal silos and hermetic super bags were more effective than conventional storage vessels in reducing contamination of maize with AFB1 during storage. Number of households exposed to AFB1 and the levels of exposure to AFB1 were higher in users of conventional storage vessels than in users of hermetic metal silos and hermetic super bags.