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 beverage oshikundu , 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 into oshikundu . A total of 105 samples (40 sorghum malt, 40 pearl millet, 25 oshikundu ) 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 from Aspergillus flavus ; helvolic acid, gliotoxin and fumiquinazolines from Aspergillus fumigatus and cytochalasin E, patulin and tryptoquivalines from Aspergillus 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 by Fusarium , Penicillium , Alternaria and Claviceps genera, respectively. European Union legislated mycotoxins occurred in cereals at a prevalence range of 3-75%, while none were quantifiable in oshikundu . Aflatoxin B 1 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 B 1 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 in oshikundu , transfer rates from cereals to oshikundu were above 50%, necessitating the use of good quality ingredients for preparing oshikundu and assessment of consumer exposure to mycotoxins.