Publicação
Characterization of the mycoflora and the occurrence of mycotoxins in Portuguese maize
| Resumo: | The reduction of yield, quality, and nutritional value of grain cereals by filamentous fungi and subsequent contamination with mycotoxins is of great concern around the world. Mycotoxins are known to cause serious health problems in animals and some mycotoxins such as aflatoxins, fumonisins and ochratoxins, in particular, have also been associated with human health problems. Aflatoxins, fumonisins and ochratoxin A produced by several Aspergillus species are prominent among the mycotoxins associated to maize economic losses (Zea mays L.). However, the presence of a given fungus does not mean that the mycotoxin(s) associated with that fungus is (are) also present. There are many factors, especially environmental conditions and agricultural practices, involved in the production of mycotoxins. The aim of this thesis was to contribute to the risk assessment of post-harvested contamination of maize kernels with aflatoxins (AFs), cyclopiazonic acid (CPA), fumonisins B1 and B2 (FB1 and FB2, respectively) and ochratoxin A (OTA) in three Portuguese regions (Beira Litoral, Ribatejo e Alto Alentejo). To this end, studies were made, first to determine maize Aspergillus mycoflora and assess the mycotoxigenic potential of the isolated strains, and secondly to determine the incidence of AFs, CPA, OTA and FB in milled maize. Ninety five maize samples were collected between November 2008 and April 2009 in maize association of producer’s facilities in three different agroclimatic regions of Portugal. These samples were taken at reception, after drying and after storage, and moisture content was measured immediately after sampling. Strains of Aspergillus were isolated and identified through phenotypic characterization and mycotoxin production. Molecular work was also done in eight isolates that could not be fully identified, up to species level, and a new species belonging to Aspergillus section Flavi was described and named as Aspergillus mottae Around ninety one percent of the maize samples were contaminated with strains of Aspergillus. These were subsequently grouped into five sections: Flavi (423 isolates) followed by Nigri (270 isolates), Wentii (214 isolates), Circumdati (15 isolates) and Candidus (2 isolates). The fungal frequency of the isolations obtained from the samples belonging to the three steps of the maize storage chain differs. The highest frequency occurs after drying, being the lowest frequency at reception followed by storage. What concerns Aspergillus species isolations at each region, the regions with Mediterranean climates had a higher percentage of Aspergillus section Nigri isolates in comparison with the region with transitional between Atlantic and Mediterranean climate. Maize samples were analyzed by HPLC for mycotoxin contamination. Mycotoxins were detected in 83% of the samples, with prevalence for FB1. Hence, 83% percent of the samples were positive for FB1, 46% were positive for FB2 and only 5% were positive for AFs. None of the samples were positive for OTA and CPA. In conclusion, the two Producer’s Society and the Agricultural Cooperative showed to have good practices, minimizing the occurrence of mycotoxins. Even though Aspergillus section Flavi, especially of A. flavus, and Aspergillus section Nigri isolates were present in high numbers in the maize kernels, very few samples were contaminated with aflatoxins (5%), and none were positive for either CPA and OTA. The presence of fumonisins (FB1 and FB2) in the majority of the samples (83 and 46%, respectively) suggests that there was pre-harvest contamination with Fusarium species. There is no evidence that the presence of FB2 is due to the presence of Aspergillus niger aggregate isolates. |
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| Autores principais: | Soares, Célia Maria Gonçalves |
| Assunto: | Maize Mycotoxigenic Fungi Aflatoxins Cyclopiazonic acid Fumonisins Ochratoxin A Aspergillus section Flavi Aspergillus section Nigri Milho Fungos micotoxigénicos Aflatoxinas Ácido ciclopiazónico Fumonisinas Ocratoxina A Aspergillus secção Flavi Aspergillus secção Nigri |
| Ano: | 2012 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | The reduction of yield, quality, and nutritional value of grain cereals by filamentous fungi and subsequent contamination with mycotoxins is of great concern around the world. Mycotoxins are known to cause serious health problems in animals and some mycotoxins such as aflatoxins, fumonisins and ochratoxins, in particular, have also been associated with human health problems. Aflatoxins, fumonisins and ochratoxin A produced by several Aspergillus species are prominent among the mycotoxins associated to maize economic losses (Zea mays L.). However, the presence of a given fungus does not mean that the mycotoxin(s) associated with that fungus is (are) also present. There are many factors, especially environmental conditions and agricultural practices, involved in the production of mycotoxins. The aim of this thesis was to contribute to the risk assessment of post-harvested contamination of maize kernels with aflatoxins (AFs), cyclopiazonic acid (CPA), fumonisins B1 and B2 (FB1 and FB2, respectively) and ochratoxin A (OTA) in three Portuguese regions (Beira Litoral, Ribatejo e Alto Alentejo). To this end, studies were made, first to determine maize Aspergillus mycoflora and assess the mycotoxigenic potential of the isolated strains, and secondly to determine the incidence of AFs, CPA, OTA and FB in milled maize. Ninety five maize samples were collected between November 2008 and April 2009 in maize association of producer’s facilities in three different agroclimatic regions of Portugal. These samples were taken at reception, after drying and after storage, and moisture content was measured immediately after sampling. Strains of Aspergillus were isolated and identified through phenotypic characterization and mycotoxin production. Molecular work was also done in eight isolates that could not be fully identified, up to species level, and a new species belonging to Aspergillus section Flavi was described and named as Aspergillus mottae Around ninety one percent of the maize samples were contaminated with strains of Aspergillus. These were subsequently grouped into five sections: Flavi (423 isolates) followed by Nigri (270 isolates), Wentii (214 isolates), Circumdati (15 isolates) and Candidus (2 isolates). The fungal frequency of the isolations obtained from the samples belonging to the three steps of the maize storage chain differs. The highest frequency occurs after drying, being the lowest frequency at reception followed by storage. What concerns Aspergillus species isolations at each region, the regions with Mediterranean climates had a higher percentage of Aspergillus section Nigri isolates in comparison with the region with transitional between Atlantic and Mediterranean climate. Maize samples were analyzed by HPLC for mycotoxin contamination. Mycotoxins were detected in 83% of the samples, with prevalence for FB1. Hence, 83% percent of the samples were positive for FB1, 46% were positive for FB2 and only 5% were positive for AFs. None of the samples were positive for OTA and CPA. In conclusion, the two Producer’s Society and the Agricultural Cooperative showed to have good practices, minimizing the occurrence of mycotoxins. Even though Aspergillus section Flavi, especially of A. flavus, and Aspergillus section Nigri isolates were present in high numbers in the maize kernels, very few samples were contaminated with aflatoxins (5%), and none were positive for either CPA and OTA. The presence of fumonisins (FB1 and FB2) in the majority of the samples (83 and 46%, respectively) suggests that there was pre-harvest contamination with Fusarium species. There is no evidence that the presence of FB2 is due to the presence of Aspergillus niger aggregate isolates. |
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