Diversity and fate of fungal metabolites during the preparation ofoshikundu, a Namibian traditional fermented beverage

Abstract

Sorghum and pearl millet, ingredients for the popular Namibian traditional fermented beverageoshikundu, are prone to fungal infection, raising concerns for consumer health from mycotoxin exposure. This study aimed at determining the diversity of fungal metabolites in street-vended ingredients and their transfer rates intooshikundu. A total of 105 samples (40 sorghum malt, 40 pearl millet, 25oshikundu) were analysed for 700 fungal, bacterial and plant metabolites, using liquid chromatography-tandem mass spectrometry. Of 98 quantified metabolites, 84 were fungal, some being mycotoxins.Aspergillus metabolites were most prevalent (50%, n=42), including aflatoxins, aflatoxin precursors, cyclopiazonic acid and 3-nitropropionic acid fromAspergillus flavus; helvolic acid, gliotoxin and fumiquinazolines fromAspergillus fumigatus and cytochalasin E, patulin and tryptoquivalines fromAspergillus clavatus. High levels of up to 2,280 μg/kg for cyclopiazonic acid and 11,900 μg/kg for 3-nitropropionic acid were quantified in sorghum malts. Other metabolites included fumonisins, curvularin, alternariol and dihydroergosine produced byFusarium,Penicillium,Alternaria andClaviceps genera, respectively. European Union legislated mycotoxins occurred in cereals at a prevalence range of 3-75%, while none were quantifiable inoshikundu. Aflatoxin B1 was quantified in pearl millet meals (13%) and sorghum malts (50%), with 15% sorghum malts having levels above the European Union regulatory limit of 5 μg/kg. Fumonisin B1 was quantified in pearl millet meals (50%) and sorghum malts (75%) at maximum levels of 3,060 μg/kg and 123 μg/kg respectively, and levels in 5% pearl millet meals were above the European Union regulatory limit of 2,000 μg/kg. Zearalenone and ochratoxin A were quantified in the cereals at levels below European Union regulatory limits. For most metabolites quantifiable inoshikundu, transfer rates from cereals tooshikundu were above 50%, necessitating the use of good quality ingredients for preparingoshikundu and assessment of consumer exposure to mycotoxins.