Determination of aflatoxin levels in stored white maize ( Zea mays L.) and flour in Kitui, Mwingi and Makueni Districts in Kenya
Kimani, Pius Mutisya
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Aflatoxins are fungal metabolites which are toxic, mutagenic and carcinogenic and thus cause undesirable effects on animal and human health when ingested with feed or foodstuffs. Aflatoxin producing fungi may occur in certain food products in form of spores, and thus when conditions are favourable, the fungi germinate and may produce aflatoxin in varied amounts. Ingestion of higher dose of aflatoxin (Codex Commission upper limit is 1 Oppb), may result in aflatoxicosis which manifests as hepatoxicity or in severe cases, fulminant liver failure. The fungi grow on starchy foodstuffs such as groundnuts, pearl millet, finger millet, maize grain and maize flour, oats and sorghum in certain conditions. Maize is a staple foodstuff for over 90% of the Kenyan population. Outbreaks of aflatoxin poisoning and aflatoxicosis associated with contaminated maize grain has been reported over the years in Kitui, Mwingi and Makueni districts in Kenya. Despite this no study to date has been carried out to exactly define the prevailing circumstances that may favour occurrence of this problem in the affected districts. A study to determine and correlate aflatoxin levels, storage temperature and moisture content in stored maize grain and grain flour was done in the three districts. The sample size was determined to be 130. A stratified random sampling technique was used, where 14 strata were identified. One (1) kg sample each of maize grain and flour, was collected from each store in the strata. Storage temperature and moisture contents were determined in situ. Sample aflatoxin levels were determined by the ELISA method. Data analysis was done by a computer software, SPSS® version 11.51, lead technology 2001, USA. In maize grain overall mean storage temperature was 29.6°C, mean moisture content 12.57% and aflatoxin level 13.17 ppb. A statistically significant (p<O.Ol), positive correlation (+ 0.954) was found between grain moisture content and aflatoxin levels. The correlation between grain storage temperature and aflatoxin levels was + 0.115, while that between the temperature and moisture content was statistically significant (p<O.Ol), at +0.05. A highly significant non association (X2 = 2.525; p < 0.05) was found between district of origin and aflatoxin contamination of grain. In maize flour, a highly significant non association (X2 = 0.696; p < 0.05) was found between the district of origin and aflatoxin contamination. The correlation between flour storage moisture content and aflatoxin level was + 0.642. That of temperature and moisture content in flour + 0.224. The values were statistically significant (p<O.Ol). Storage moisture content and temperature level in maize grain and maize flour favour production of aflatoxins, however the effect of moisture content is higher than that of temperature. The prevalence of aflatoxin contamination was higher (84.6%) and mean lower (13.17ppb), in maize grain than in flour (79.5%) and higher mean (21.34 ppb) from the same market stores. Mwingi district had lower aflatoxin mean (9.67 ppb), moisture content mean (12.17%), and storage temperature mean at 26.43°C. Makueni had higher mean values at 16.67 ppb, 12.55%, and 31.47°C, respectively. Consequently by inference, maize grain and flour should be stored at 26.4°C or less, and dried down to moisture content of 12.2% or less before storage. The risks of aflatoxin contamination is higher in flour than in maize grain (13.17 ppb <21.54 ppb> 10.00 ppb). Thus, milling grain to flour should be done at moisture content of 12.2% or less, to discourage growth of aflatoxin producing fungi. This information will be submitted to Ministry of Agriculture and used to advice on correct storage temperature and moisture for maize grain and flour.