Analysis of the contrast between natural occurrence of toxigenic Aspergilli of the Flavi section and aflatoxin B1 in cassava.

Aflatoxin B1 (AFB1) is a carcinogenic mycotoxin produced by Aspergilli of the section Flavi that may contaminate food, in the field or during storage. Cassava represents an important staple food in sub-Saharan Africa. The analysis of aflatoxigenic fungi in 36 cassava samples obtained from producers in Benin indicated that 40% were contaminated by Aspergilli of the section Flavi. Upon morphological and molecular characterization of the 20 isolates, 16 belonged to Aspergillus flavus, 2 to Aspergillus parvisclerotigenus and 2 to Aspergillus novoparasiticus. This is the first time that this latter species is isolated from food. Although most of these isolates were toxigenic on synthetic media, no AFB1 contamination was observed in these cassava samples. In order to determine the action of cassava on AFB1 synthesis, a highly toxigenic strain of A. flavus, was inoculated onto fresh cassava and despite a rapid development, no AFB1 was produced. The anti-aflatoxin property was observed with cassava from different geographical origins and on other aflatoxigenic strains of the section Flavi, but it was lost after heating, sun drying and freezing. Our data suggest that fresh cassava is safe regarding AFB1 contamination, however, processing may alter its ability to block toxinogenesis leading to secondary contamination.

Production and stability of patulin, ochratoxin A, citrinin, and cyclopiazonic acid on dry cured ham.

Toxinogenic fungal species can be isolated from dry cured meat products, raising the problem of the direct contamination of these foods by mycotoxins known to be carcinogenic or potent carcinogens. Because the contamination of a food by mycotoxins can be considered a balance between production and degradation, the stability of mycotoxins on dry cured meat was also investigated. This study focused on patulin, ochratoxin A, citrinin, and cyclopiazonic acid that can be produced by fungal species previously isolated from dry cured meat products sold on the French market. We demonstrated that neither patulin nor ochratoxin A was produced on dry meat by toxigenic strains, whereas relatively high amounts of citrinin and cyclopiazonic acid were found after a 16-day incubation period at 20 degrees C (87 and 50 mg/kg, respectively). After direct contamination, the initial content of patulin rapidly decreased to become undetectable after only 6 h of incubation at 20 degrees C. For both citrinin and ochratoxin A, the kinetics of decrease at 20 degrees C was less rapid, and the two toxins presented half-lives of 6 and 120 h, respectively. By contrast, more than 80% of the initial contamination in cyclopiazonic acid was still found on ham after a 192-h incubation period. Toxin stability was not affected by storage at 4 degrees C. These results suggest that growth of toxigenic strains of Penicillium has to be avoided on dry meat products.

Citrinin production and stability in cheese.

Citrinin is a nephrotoxic fungal metabolite that has been demonstrated to be mutagenic in hepatocytes. It can be produced by several fungal species that belong mainly to the genus Penicillium and has been isolated from many feeds and human foods. Cheese is a very sensitive product because it can be naturally contaminated by citrinin-producing molds. The purpose of this study was to determine whether citrinin can be produced in cheeses and whether it is stable in these products. Both toxigenic strains of Penicillium citrinum and Penicillium expansum used were able to produce citrinin in cheese at 20 degrees C, but not at 4 degrees C. Up to 600 mg of citrinin per kg of cheese was obtained after 10 days of incubation. Interestingly, fresh goat cheese appeared to be a more favorable substrate for toxigenesis than did yeast extract-sucrose medium. Although contamination was mainly superficial, 33% of the toxin remained in cheese after trimming. Moreover, citrinin appeared to be very stable in some of the tested cheeses (goat cheese, Saint Marcellin, Soignon). For all cheeses tested, more than 50% of the initial content of citrinin was still present after 8 days of storage. Taken together, these results suggest that the contamination of cheeses by wild strains of Penicillium must be avoided.