Modelling the effect of temperature and water activity of Aspergillus flavus isolates from corn.

The aim of this study was to model the effects of temperature (10-40 °C) and a(w) (0.80-0.98), in two media (Czapek yeast agar: CYA; corn extract medium: CEM) on the growth rates and growth boundaries (growth-no growth interface) of three strains of A. flavus isolated from corn in Argentina. Both kinetic and probability models were applied to colony growth data. The growth rates obtained in CYA were significantly (p<0.05) greater than those obtained in CEM medium. No significant differences (p<0.05) were observed among the three isolates. The growth rate data showed a good fit to the Rosso cardinal models combined with the gamma-concept with R(2)=0.98-0.99 and RMSE=0.60-0.78, depending on media and isolates. The probability model allowed prediction of safe storage (p of growth <0.01) for one month for moist maize (e.g. 0.90 a(w)) provided temperature is under 15 °C, or for dry maize (e.g. 0.80 a(w)) provided temperature is under 27 °C. Storage at <0.77 a(w) would be safe regardless of the storage temperature. Probability models allow evaluation of the risk of fungal contamination in the process of storage, so the results obtained in this study may be useful for application in systems of food safety management.

A survey on distribution and toxigenicity of Aspergillus section Flavi in poultry feeds.

Thirty-five samples of poultry feeds and corresponding raw materials (maize, soybean and meat meal) from a processing plant were analyzed to evaluate the distribution and toxigenicity of Aspergillus section Flavi isolates. Mycological analysis of the samples indicated the presence of five fungal genera (Aspergillus, Penicillium, Fusarium, Cladosporium, and Eurotium). Aspergillus flavus was the predominant species being present in 48.5% of the analyzed samples. Ninety-one isolates belonging to Aspergillus section Flavi were isolated; ninety were identified as A. flavus and only one as A. parasiticus. Fifty-seven isolates were capable of producing sclerotia, 41 were identified as L-type strains and 16 as type S. Fifty-seven percent of the isolates produced AFB1 levels ranging from 0.05 µg/kg to 27.7 µg/kg whereas 86.8% produced CPA from 1.5 µg/kg to 137.8 µg/kg. L-strains produced from 0.05 to 14.8 µg/kg of aflatoxin and type S produced levels from 0.05 to 1.65 µg/kg. No significant differences in CPA production among S- and L-strains were observed. Sclerotial isolates produced AFB1 levels ranging between 0.05 and 27.7 µg/kg and CPA levels from 3.8 to 47.3 µg/kg. More than half of the A. flavus isolates were able to produce AFB and CPA simultaneously. Twenty percent of the 35 samples were contaminated with aflatoxin B1 whereas 34.3% were contaminated with CPA. The high rate of CPA producing isolates represents a potential risk of contamination with this toxin in poultry feeds.

Food-grade antioxidants and antimicrobials to control growth and ochratoxin a production by Aspergillus section Nigri on peanut kernels.

Each year, a significant portion of the peanuts produced cannot be marketed because of fungal disease at the postharvest stage and mycotoxin contamination. Antioxidants could be used as an alternative to fungicides to control ochratoxigenic fungi in peanuts during storage. This study was carried out to determine the effect of the antioxidant butylated hydroxyanisole (BHA) and the antimicrobial propyl paraben (PP) on the lag phase before growth, growth rate, and ochratoxin A (OTA) production by Aspergillus section Nigri strains in peanut kernels under different conditions of water activity (aw) and temperature. At 20 mM/g BHA, 18 degrees C, and 0.93 aw, complete inhibition of growth occurred. For PP, there was no growth at 20 mM/g, 18 degrees C, and 0.93, 0.95, and 0.98 aw. BHA at 20 mM/g inhibited OTA production in peanuts by Aspergillus carbonarius and Aspergillus niger aggregate strains at 0.93 aw and 18 degrees C. PP at 20 mM/g completely inhibited OTA production at 18 degrees C. The results of this work suggest that PP is more appropriate than BHA for controlling growth and OTA production by Aspergillus section Nigri species in peanut kernels.

Production of citreoviridin by Penicillium citreonigrum strains associated with rice consumption and beriberi cases in the Maranhão State, Brazil.

The aim of this study was to determine the levels of Penicillium citreonigrum and citreoviridin present in rice samples from Maranhão State, Brazil, where an outbreak of beriberi was reported and 32 deaths occurred (7% of the notified cases died in 2006). The ability of P. citreonigrum to produce citreoviridin was assessed, and a total of 420 samples of 21 different kinds of rice were collected. Mycobiota isolation and identification, the ability of citreoviridin strains to produce toxin, and the natural occurrence of citreoviridin were established. Rice samples were found to have high fungal counts and showed increasing levels from 2004 to 2007 harvest years. The most frequent genus was Aspergillus followed by Penicillium and Cladosporium. Ten out of eleven strains of P. citreonigrum were able to produce citreoviridin. Three rice samples had levels of citreoviridin ranging from 12 to 96.7 ng g(-1), and two bran samples had levels of 128 and 254 ng g(-1). These samples contaminated with P. citreonigrum and citreoviridin were involved in the beriberi cases from Maranhão State. Monitoring rice for mycotoxins in areas where this substrate is the basic food is crucial to prevent outbreaks like the one reported in this study, to improve management practice, and to diminish exposure risk of humans to these harmful toxins.

Ecophysiological factor effect on growth rate, lag phase and ochratoxin A production by Aspergillus niger aggregate strains on irradiated peanut seeds.

The aims of this study were to evaluate the effects of water activity, temperature, incubation time and their interactions on lag phase, growth rate and ochratoxin A (OTA) production by strains belonging to the Aspergillus niger aggregate on irradiated peanut seeds. In the temperature and water activity range assayed, the optimal conditions of growth for RCP42 and RCP176 strains on irradiated peanut seeds were 0.995 a(w) and 30 degrees C being the growth rates of 12.4 and 14.6 mm/day, respectively. The maximum OTA production occurred at 0.973 a(w) and 25 degrees C for both strains assayed; whereas the minimum OTA production was obtained at 0.951 a(w) and 15 degrees C, at 14 and 21 days of incubation for RCP42 and RCP176 strains, respectively. The amount of OTA accumulated during 21 days assayed by both strains varied from 6.5 to 460 microg/g and from 10 to 210 microg/g with mean levels of 119.2 and 97.5 microg/g for RCP42 and RCP176 strains, respectively. The variance analysis (ANOVA) revealed that OTA concentration produced by RCP42 strain was significantly (p<0.0001) greater than that produced by RCP176 strain. If the strains with which the experiments were carried out were representative of the Aspergillus niger aggregate toxigenic species and the water activity in peanut seeds stored at 0.910 or lower was maintained, OTA production would be reduced during at least 21 days at variable temperatures.

Fungi and selected mycotoxins from pre- and postfermented corn silage.

AIM: To determine fungal genera, Aspergillus and Fusarium species and aflatoxin B(1) (AFB(1)), zearalenone (ZEA), deoxynivalenol (DON), fumonisin B(1) (FB(1)) contamination from pre- and postfermented corn silage produced in the most important region of Argentina where silage practice is developed. METHODS AND RESULTS: Sampling of corn silos was performed manually through silos in transects at three levels: upper, middle and low sections. AFB(1) and FB(1) were quantified by high-performance liquid chromatography, zearalenone by enzyme-linked immunosorbent assay and DON by gas chromatography. Over 90% of the samples showed counts higher than 1 x 10(4) CFU g(-1). Aspergillus flavus and Fusarium verticillioides were the prevalent species. Some tested samples were contaminated with AFB(1), ZEA, DON and FB(1). CONCLUSIONS: This study demonstrates the presence of fungi and AFB(1), ZEA, DON and FB(1) contamination in corn silage in Argentina. SIGNIFICANCE AND IMPACT OF THE STUDY: This manuscript makes a contribution to the knowledge of mycotoxins in Argentinean silage in particular because the environmental conditions in this country differ from those of most reports. The comparison of pre- and postfermentation silage is also outstanding. Therefore, information on fungi and mycotoxins present in silage--an increasingly popular commodity--is useful to estimate potential risk for animal and human health.

Ochratoxin A production in relation to ecophysiological factors by Aspergillus section Nigri strains isolated from different substrates in Argentina.

Contamination of foodstuff with mycotoxins such as ochratoxins is a major matter of concern for human and animal health. In Aspergillus species, ochratoxin synthesis depends on several environmental factors. The aims of this work were to evaluate the effect of water activity (0.995-0.85), temperature (15, 25 and 30 degrees C), incubation time (7, 14 and 21 days) and their interactions on OTA production on peanut, maize kernels, dried grapes and coffee beans meal extract agar medium by eight strains of Aspergillus section Nigri isolated from human food in Argentina. The optimum temperature for OTA production was 25 or 30 degrees C depending on the strains assayed, in most cases the highest OTA levels were achieved after 7 days of incubation, whereas this situation occurred at 15 degrees C after 14 days of incubation for only one strain. The maximum OTA level was obtained at earlier growth states when incubation temperature increased. In general, OTA concentration increased as water activity (a(W)) increased with no significant production at 0.85-0.91 a(W) under all temperature levels tested. Production occurred over a range of temperatures (15-30 degrees C) with optimum production at 30 degrees C depending on a(W) assayed. The knowledge of Aspergillus section Nigri ecophysiology is critical in the development and prediction of the risk models of raw material and final product contamination by these species under fluctuating and interacting environmental parameters.

Surveillance of toxigenic fungi and ochratoxin A in feedstuffs from Córdoba Province, Argentina.

The aim of this work was to evaluate the incidence of potential ochratoxigenic mycoflora and ochratoxin A (OA) in poultry, pig and rabbit feeds. Eighty poultry, pig and rabbit feed samples were taken at random from factories located from Córdoba province, Argentina, over a period of 8 months. Isolation and quantitative enumeration of fungal propagules were done on DRBC and DG18 media. The predominant species were A. candidus, A. flavus, A. terreus, A. parasiticus, P. implicatum, P. minioluteum, P. crustosum and P. citrionigrum. The distribution of section Nigri species varied according to the feedstuffs analysed. The frequency of A. niger var. niger was noticeably high in poultry feed samples on DRBC medium. The Nigri section species was present at moderate mean colony counts (CFU/g) from three feeds. Mycotoxin analysis of these samples showed that OA was detected in 15%, 10% and 12% of pig, poultry and rabbit feed samples, respectively. The mean levels detected ranged between 15 and 25 ng/g from three feeds. The presence of ochratoxigenic species of Nigri section and OA in feeds indicates the risk of potential exposure of poultry, pigs and rabbits through the ingestion of feeds.

Survey of mycoflora and ochratoxin A in dried vine fruits from Argentina markets.

AIMS: The aims of this work were to identify the mycoflora and to evaluate the natural occurrence of OA in dried vine fruits. Likewise, the capacity to produce OA by Aspergillus section Nigri was studied. MATERIALS AND METHODS: Fifty samples of dried vine fruits were obtained from Mendoza and San Juan provinces. The surface disinfection method was used for mycoflora determination using the medium dichloran 18% glycerol agar (DG18) and dichloran Rose Bengal chloramphenicol agar (DRBC). RESULTS: Statistical analysis demonstrated that the species A. niger var. niger and Aspergillus niger var. awamori were isolated in higher frequency from black dried vine fruits from DRBC and DG18 media (P < 0.01). OA was found in 74% of the dried vine fruits samples. Sixty-two strains (28%) of Aspergillus section Nigri, were OA producers. In the species A. carbonarius the highest percentages of ochratoxigenic strains were detected (82.6%). CONCLUSIONS: The presence of ochratoxigenic strains of Nigri section in dried vine fruits suggests that they may be an important source of OA in this substrate. Dried vine fruits can also be an important source of OA people who consume large amounts. SIGNIFICANCE AND IMPACT OF THE STUDY: The dried vine fruits contamination with Aspergillus section Nigri and OA was significant.