Mycological and Multiple Mycotoxin Surveillance of Sorghum and Pearl Millet Produced by Smallholder Farmers in Namibia

Mycological (mycotoxigenic Fusarium and aflatoxigenic Aspergillus spp.) and multiple mycotoxins [aflatoxin B-1 (AFB(1)), fumonisin B (FB), deoxynivalenol and zearalenone] surveillance was conducted on raw whole grain sorghum (Sorghum bicolor) and pearl millet (Pennisetum glaucum) produced on smallholder farms, and processed products sold at open markets in northern Namibia. Fungal contamination was determined with morphological methods as well as with quantitative Real-Time PCR (qPCR). The concentrations of multiple mycotoxins in samples were determined with liquid chromatography tandem mass spectrometry. The incidence of mycotoxigenic Fusarium spp., Aspergillus flavus and A. parasiticus, as well as the concentrations of AFB(1) and FB were significantly (P < 0.001) higher in the malts as compared to the raw whole grains, with Aspergillus spp. and AFB(1) exhibiting the highest contamination (P < 0.001). None of the analysed mycotoxins were detected in the raw whole grains. Aflatoxin B-1 above the regulatory maximum level set by the European Commission was detected in sorghum (2 of 10 samples; 20%; 3-11 mu g/kg) and pearl millet (6 of 11 samples; 55%; 4-14 mu g/kg) malts. Low levels of FB1 (6 of 10 samples; 60%; 15-245 mu g/kg) were detected in sorghum malts and no FB was detected in pearl millet malts. Contamination possibly occurred postharvest, during storage, and/or transportation and processing. By critically monitoring the complete production process, the sources of contamination and critical control points could be identified and managed. Mycotoxin awareness and sustainable education will contribute to reducing mycotoxin contamination. This could ultimately contribute to food safety and security in northern Namibia where communities are exposed to carcinogenic mycotoxins in their staple diet.

Automated summary

This study conducted surveillance on mycotoxins in raw whole grain sorghum and pearl millet produced in smallholder farms and sold at open markets in northern Namibia. The analysis revealed higher concentrations of mycotoxigenic Fusarium species, Aspergillus flavus, and AFB(1) and FB in malts compared to raw whole grains. Aflatoxin B1 levels exceeded the maximum regulatory level set by the European Commission. The contamination likely occurred during postharvest, storage, transportation, and processing stages.