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.
The mold incidence, moisture contents, pH and levels of mycotoxins (aflatoxins B1, G1 and ochratoxin A) on/of/in rootstock snack (tubers of Cyperus esculentus L.) samples were monitored during a 150-day storage period. Whereas the mold incidence, moisture and mycotoxin levels increased with storage time, the pH declined during the same period. Altogether, 12 fungal species, mostly toxigenic, including Aspergillus flavus, A. parasiticus and A. ochraceus were isolated. At collection period only 3 of the 9 snack samples analysed contained trace amounts of aflatoxins. By 120th day, all the 9 samples were contaminated and the average levels were 454 and 80 ppb for aflatoxin B1 and aflatoxin G1 respectively on the 150th day. Ochratoxin A was not detected before 120th day and then only at low levels, occurring in a maximum of four-samples and ranging between 10 and 80 ppb.
SummaryAflatoxin producing strains of Aspergillus flayus Link (IMI 280819) and A . oryzae (Ahlb.) Cohn (IMI 280831) were among the eleven spoilage moulds isolated from five types of poultry feeds. The recorded pH and moisture content values of the various feeds are conducive to mould deterioration. All the four principal aflatoxins (B,, B,, G I , G2) were detected in the analysed feeds though at toxicologically 'safe' levels for most farm animals. Significant quantities of aflatoxin B, were produced by the two fungal isolates in all the five classes of poultry feeds with A.flauus yielding the larger amounts. Optimum aflatoxin B, production and mycelial growth in chick mash infusion medium were recorded for both species at 30 and 35 "C, respectively and similarly on the 8th and 6th day respectively when cultures were incubated at 30 "C.
Both the moisture levels and the incidence of mould contamination recorded for shelled water melon seed samples (22) obtained from 9 markets were generally higher as those recorded for the unshelled seed samples. 16 fungi, mostly toxigenic, were isolated from the surface-disinfected mouldy seeds. Of these isolates, 7, 3 and 2 species belonged to Aspergillus, Penicillum and Fusarium genera, respectively, while Botryodiplodia, Rhizopus, Sclerotium and Syncephalastrum had one representative each. Production of aflatoxins (B1, B2) by 5 toxigenic strains of Aspergillus flavus and of ochratoxin A by 4 toxigenic strains of A. ochraceus in melon seed at varying water activity (aw) and temperature levels were investigated. Of the aw levels (0.65, 0.70, 0.80, 0.90 and 0.98) provided, toxins were detected only at and above 0.80 with the peak production recorded at either 0.90 or 0.98 aw level. Whereas aflatoxins were produced and detected under all the test temperatures (15, 20, 25, 30, 35, and 40 degrees C), the elaboration of ochratoxin A was detected only as from 25 to 40 degrees C. Optimum temperature for toxin production by all the strains of the two fungi used was 30 degrees C.
A total of 14 moulds were isolated from 84 samples of cured fish obtained from several processing centres and retail shops in Lagos, Ogun and Oyo States, Nigeria. Aspergillus niger, A. flavus and A. chevalieri were the most prevalent. With the exception of Basipetospora sp., slight inhibition of mycelial growth and/or sporulation was recorded when isolates were cultured in basal medium containing 5% sodium chloride. The extent of inhibition increased with increasing salt concentrations, and at 25% level all the species had their growth completely inhibited. When fish substrates inoculated with test fungi were kept inside 65% relative humidity (RH) chambers for 21 days, no detectable utilization of the substrates was recorded for any of the fungal species. Whereas only A. chevalieri and A. restrictus utilized the substrates when placed inside 70% RH chambers, all the test moulds recorded detectable utilization (though at varying extents) of same at 80% and 90% RH levels. The latter RH was the most conductive and under it A. niger, Penicillium sp. and the two isolated Scopulariopsis sp. brought about the greatest loss in weight of the substrates.
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