Mycoflora, and mycotoxins production in Nigerian corn and corn-based snacks

Thirty-one fungal species, mostly toxigenic and belonging to 11 genera were isolated from corn, corn cake and corn roll snack samples. Aspergillus, Penicillium and Fusarium accounted for 10, 6 and 3 of the species and altogether, they constituted 90, 94 and 88 percent of the total fungi in corn, corn cake and corn roll snack respectively. Mycotoxins (aflatoxins and ochratoxin A) were detected in 45, 80 and 12 percent while the means and ranges of the total aflatoxins recorded were: 200(25-770 ppb); 233(15-1070 ppb) and 55(10-160 ppb) for corn, corn cake and corn roll snack samples respectively. Ochratoxin A was detected at toxicologically significant levels in only 15 percent of the corn cake samples analyzed. All the strains of Aspergillus flavus and A. ochraceus tested produced aflatoxin B and ochratoxin A, respectively, when they were cultured on each of the three substrates. In each case, substantial quantities of the toxins were produced from 25 to 35 degrees C with the peak level recorded at 30 degrees C. Toxin production was detected only in substrates with 15 percent moisture content and above; reaching the maximum at 25 or 30 percent moisture level. No substantial differences in the amount of toxins were elaborated with further increase in substrates' moisture content. Of the three substrates, corn cake was the most suitable for aflatoxin B production while they were all equally suitable for the elaboration of ochratoxin A.