Fungi, aflatoxins, fumonisin B-1 and zearalenone contaminating sorghum-based traditional malt, wort and beer in Botswana

Brewing and consumption of traditional beer have social-economic significance in most African countries including Botswana. Traditional sorghum malt, wort, and beer samples were collected from three villages around Gaborone, Botswana. Forty-six malt samples were analyzed for fungi on three different media and developing colonies were subcultured for identification. Rhizopus, Fusarium, Mucor, and Aspergillus were the most common genera isolated. Out of the 46 malt samples, 72% contained Rhizopus stolonifer, 63% Fusarium verticillioides (syn. Fusarium moniliforme), and 37% Aspergillus flavus. Although Aspergillus flavus was isolated from malt samples, aflatoxins (B-1, B-2, G(1), and G(2)) were not detected in any of the samples analyzed. When the malt, wort, and beer samples were analyzed for fumonisin B-l and zearalenone, fumonisin B-1 was detected in 3 malt samples, with concentrations ranging from 47 to 1316 mu g/kg, while zearalenone was detected in 56%, 48% and 48% of the malt, wort and beer samples, respectively. Zearalenone concentration in samples ranged from 102 to 2213 mu g/kg in malt, 26 to 285 mu g/l in wort and 20 to 201 mu g/l, in beer. Zearalenone carry-over from wort to beer ranged from 23 to 403%. Therefore, although aflatoxins and fumonisin B-1 do not appear to be major contaminants, zearalenone is common and could pose a potential problem in traditional beer in Botswana.