Assessment of aflatoxin-producing fungi strains and contamination levels of aflatoxin B1 in groundnut, maize, beans and rice

Aflatoxins are polyketide-derived, toxic and carcinogenic secondary metabolites produced by some species of Aspergillus and other fungi on food crops and feed. Aflatoxin B1 is classified as the most toxic of the aflatoxins, responsible for not only great economic loss but is also the most potent naturally occurring chemical liver carcinogen known. Random samples of groundnut, maize, beans and rice were collected from the Kumasi Central Market and analyzed for their aflatoxin levels using High Performance Liquid Chromatography (HPLC). Furthermore, molecular assessment of aflatoxin-producing fungi in the grain samples involving five pairs of universal and eight specific aflatoxin primers were carried out. The contamination levels found ranged from trace amount to 31.11 ppb, with groundnut registering the highest aflatoxin content. A further microbial culture examination revealed that most of the crop samples, especially groundnut and maize were susceptible to various species of aflatoxigenic, A. flavus, A. paraciticus, A. tamarii, P. expansum, Mucor hiemalis, A. niger, P. citrinum, Moniliellaspp. and other toxigenic fungi. Colony forming units per gram (CFU/g) from the microbial cultures ranged from 4.3×10 6 to 2.1×10 3 . However, a poor correlation existed between the aflatoxin contamination level and the CFU/g per sample. A consistent correlation could not be made between the molecular analysis and microbial results. Just as in A. versicolor, four universal primers, 0817F/1196R, U1/U2, FF2/FR1 and ITS1/IST2, and one specific aflatoxin producing fungi primer, Nor1/Nor2, was able to show positive bands on A. versicolor. These suggest that particular fungi have the gene to produce aflatoxin; however, it could not produce detectable aflatoxin by the HPLC. The results showed the aflatoxin levels were within acceptable limit for consumption and exportation (0-20 ppb) by Codex.