Aspergillus section Flavi and aflatoxins in Brazilian cassava (Manihot esculenta Crantz) and products

Aflatoxins are carcinogenic compounds produced by some species of Aspergillus, especially those belonging to Aspergillus section Flavi. Their occurrence in food may start in the field, in the post-harvest, or during storage due to inadequate handling and storage. Because cassava is a staple food for a high percentage of the Brazilian population, we evaluated the presence of aflatoxin-producing species in cassava tubers, cassava products (cassava flour, cassava starch, sour starch, and tapioca flour), and in soil samples collected from cassava fields. In addition, the levels of aflatoxin contamination in cassava products were quantified. A total of 101 samples were analyzed, and 45 strains of Aspergillus section Flavi were isolated. Among the identified species, Aspergillus flavus, Aspergillus arachidicola, Aspergillus novoparasiticus, and Aspergillus parasiticus were found. The majority of strains (73.3%) tested for their aflatoxin-producing ability in synthetic media was positive. Despite that, cassava and cassava products were essentially free of aflatoxins, and only one sample of cassava flour contained traces of AFB₁ (0.35 μg/kg).

Incidence of toxigenic fungi and ochratoxin A in dried fruits sold in Brazil

A total of 117 dried fruit samples (black sultanas, white sultanas, dates, dried plums, dried figs and apricots) from different origins were analysed both for toxigenic fungi and for the presence of ochratoxin A. Amongst the fungi found, Aspergillus niger was predominant, with 406 isolates, of which 15% were ochratoxin A producers. They were followed by A. ochraceus, with 15 isolates and 87% ochratoxigenics, and A. carbonarius, with only five isolates of which 60% were ochratoxin A producers. The average infection rates for A. niger in black sultanas, plums, figs, dates and white sultanas were 22.0, 8.0, 4.0, 1.5 and 0.5%, respectively. The apricot samples were not contaminated by any fungi or ochratoxin A. Black sultana and dried figs contained the highest contamination with ochratoxin A, with 33 and 26.3% of the samples containing more than 5 microg kg(-1) respectively, while all the white sultanas, dates and plums had no sample that exceeded this limit.

The source of ochratoxin A in Brazilian coffee and its formation in relation to processing methods

A total of 408 Brazilian coffee samples was examined during the 1999 and 2000 coffee harvest seasons for the presence of ochratoxin A (OA) and fungi with the potential to produce it. Samples came from four regions: Alta Paulista (western area of São Paulo State), Sorocabana (southwest São Paulo State), Alta Mogiana (northeast São Paulo State) and Cerrado Mineiro (western area of Minas Gerais State). Cherries and beans were examined at different stages: immature, mature and overripe cherries from trees, overripe cherries from the ground and beans during drying and storage on the farm. For mycological studies, the cherries and beans were surface disinfected with chlorine, plated on Dichloran 18% Glycerol Agar at 25 degrees C for 5-7 days and analysed for the presence of Aspergillus ochraceus and closely related species, A. carbonarius and A. niger. More than 800 isolates of fungi belonging to these species were identified and studied for the ability to produce OA using the agar plug technique and thin layer chromatography (TLC). A. niger was the species found most commonly (63% of isolates of these three species), but only 3% of them produced OA. A. ochraceus also occurred commonly (31% of isolates), and 75% of those studied were capable of OA production, a much higher percentage than reported elsewhere. A. carbonarius was found (6% of isolates) only in Alta Paulista, the hottest region studied, and only from beans in the drying yard or in storage. However, 77% of the A. carbonarius isolates were capable of producing OA. Average infection rates for cherries taken from trees were very low, but were higher in fruit taken from the ground, from the drying yard and from storage, indicating infection by toxigenic species after harvest. The average OA content in 135 samples of mature cherries from trees, overripe from trees, overripe from the ground, drying yard and storage was 0.1, <0.2, 1.6, 2.1 and 3.3 microg/kg, respectively. Although individual OA levels varied widely, only 9 of the 135 samples analysed exceeded 5 microg/kg OA, with one sample of poor quality dried coffee in excess of 100 microg/kg OA. The causes of high contamination were investigated on the farms concerned and several critical points were found, relating both to local climatic conditions and the drying processes used.

Comparison of culture media, simplate, and petrifilm for enumeration of yeasts and molds in food

The efficacy of three culture media, dichloran rose bengal chloramphenicol (DRBC), dichloran 18% glycerol agar (DG18), and potato dextrose agar (PDA) supplemented with two antibiotics, were compared with the Simplate and Petrifilm techniques for mold and yeast enumeration. The following foods were analyzed: corn meal, wheat flour, cassava flour, bread crumbs, whole meal, sliced bread, ground peanuts, mozzarella cheese, grated parmesan cheese, cheese rolls, orange juice, pineapple pulp, pineapple cake, and mushroom in conserve. Correlation coefficients of DRBC versus PDA and DG18 for recovering total mold and yeast counts from the composite of 14 foods indicated that the three media were generally equivalent. Correlation coefficients for Petrifilm versus culture media were acceptable, although not as good as between culture media. Correlation coefficients of Simplate versus DRBC, DG18, PDA, and Petrifilm for recovering total yeasts and molds from a composite of 11 foods demonstrated that there was no equivalence between the counts obtained by Simplate and other culture media and Petrifilm, with significant differences observed for the most foods analyzed.