Mycobiota and mycotoxin contamination of maize flours and popcorn kernels for human consumption commercialized in Spain.

Mycobiota and co-occurrence of aflatoxins, citrinin, ochratoxin A and zearalenone in 30 samples of maize flours and 30 of popcorn kernels purchased in Spain for human consumption were determined. The mycotoxin-producing ability of Aspergillus, Fusarium and Penicillium spp. was also studied. Total fungal counts of maize flours ranged from <10 to 8.4 × 10(4) CFU/g and predominant mycobiota belonged to Aspergillus spp. and Penicillium spp. In popcorn kernels samples the most frequent species were Aspergillus spp., Mucorales, Fusarium spp. and Penicillium spp. Aflatoxins were produced by Aspergillus flavus and Aspergillus parasiticus, citrinin by Penicillium citrinum and Penicillium verrucosum, ochratoxin A by Aspergillus niger and patulin by Aspergillus clavatus and Penicillium griseofulvum. Identification of all the mycotoxin-producing strains as well as some Aspergillus spp. difficult to identify using phenotypic characters only was also performed by molecular methods. Aflatoxins were detected in 14 maize flours and 2 popcorn kernels samples, while ochratoxin A was detected in 4 maize flours and 10 popcorn samples. Co-occurrence of aflatoxins and ochratoxin A was found in the 4 ochratoxin-positive maize flour samples. Citrinin and zearalenone were not detected. This is the first report of aflatoxins and ochratoxin A contamination in maize flours and popcorn kernels commercialized in Spain.

Effect of water activity, temperature and incubation time on growth and ochratoxin A production by Aspergillus niger and Aspergillus carbonarius on maize kernels.

The aim of this study was to determine the effects of water activity (a(w)) (0.92-0.98), temperature (5-45 °C) and incubation time (5-60 days) on growth and ochratoxin A (OTA) production by Aspergillus niger and Aspergillus carbonarius on maize kernels using a simple method. Colony diameters of both strains at 0.92 a(w) were significantly lower than those at 0.96 and 0.98 a(w) levels. The optimum growth temperature range for A. niger was 25-40 °C and for A. carbonarius 20-35 °C. A. niger produced OTA from 15 to 40 °C, and the highest OTA level was recorded at 15 °C. The concentration of OTA produced at 0.92 a(w) was significantly lower than those at 0.96 and 0.98 a(w). A. carbonarius produced OTA from 15 to 35 °C and the maximum concentration was achieved at 15 °C, although not differing statistically from the concentration detected at 20 °C. At 0.98 a(w) the OTA concentration was significantly higher than at 0.96 and 0.92 a(w). Our results show that maize supports both growth and OTA production by A. niger and A. carbonarius. The studied strains were able to produce OTA in maize kernels from the fifth day of incubation over a wide range of temperatures and water availabilities. Although the limit of quantification of our method was higher than that required for the analysis of OTA in food commodities, it has proved to be a useful and rapid way to detect OTA production by fungi inoculated onto natural substrates, in a similar way as for pure culture. Both species could be a source of OTA in this cereal in temperate and tropical zones of the world.

Temperature and incubation time effects on growth and ochratoxin A production by Aspergillus sclerotioniger and Aspergillus lacticoffeatus on culture media.

AIMS: As there is no knowledge of the influence of abiotic factors on the two new ochratoxin A (OTA)-producing species Aspergillus sclerotioniger and Aspergillus lacticoffeatus, the aim of this study was to evaluate the effect of temperature and incubation time on growth and OTA production by these species on culture media. METHODS AND RESULTS: The study was carried out on yeast extract sucrose agar (YES) and Czapek yeast extract agar (CYA) incubated at ten different temperatures from 5 to 50°C (at 5°C intervals). Growth assessment and OTA production were determined after 5, 10, 15, 20 and 30 days of incubation at each temperature. Aspergillus sclerotioniger grew from 10 to 35°C; OTA was detected from 10 to 35°C and the highest concentration was achieved at 15°C in CYA. Aspergillus lacticoffeatus grew from 10 to 45°C; OTA was detected from 15 to 45°C, and the maximum concentration was produced after 5 days at 25°C in YES. CONCLUSIONS: The studied species can produce OTA over a wide range of temperatures and significant amounts can be produced in only 5 days. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report on the influence of ecophysiological factors on these two ochratoxigenic species. The pattern of effects of temperature on growth and OTA production by A. sclerotioniger and A. lacticoffeatus was similar to those reported for the closely related species Aspergillus carbonarius and Aspergillus niger, respectively. The two new OTA-producing species have both been isolated from coffee beans, and the closely related ochratoxigenic species of section Nigri, A. carbonarius and A. niger are important sources of OTA in this substrate.

Comparison of two selective culture media for the detection of Fusarium infection in conventional and transgenic maize kernels.

AIMS: To assess differences between two recommended selective culture media, Nash and Snyder medium (NS) and malachite green agar 2.5 (MGA 2.5), for the detection of Fusarium infection in conventional and transgenic maize kernels. METHODS AND RESULTS: In total, 10 800 kernels from commercial varieties grown in Spain were analysed using these Fusarium selective culture media. Fusarium verticillioides was predominant in both selective culture media. Mean percentages of Fusarium infected kernels were significantly lower in transgenic maize kernels than in conventional maize kernels. There were no significant differences in percentage of Fusarium infection between the two selective culture media used, although the total mean value on MGA 2.5 (18.8%) was slightly lower than on NS (19.1%). CONCLUSIONS: MGA 2.5 performed as a potent selective medium for the detection of Fusarium infection in maize kernels using the direct plating technique. SIGNIFICANCE AND IMPACT OF THE STUDY: NS with pentachloronitrobenzene (PCNB) as fungal inhibitor is one of the most widely employed selective culture medium for Fusarium spp. However, PCNB has been reported to be carcinogenic. MGA 2.5 can be used as an alternative to NS in the detection of Fusarium infection in grain samples using the direct plating technique.