RESUMO
Maize (Zea mays L.) is an important crop in Argentina. Aspergillus section Flavi can infect this crop at the pre-harvest stage, and the harvested grains can be contaminated with aflatoxins (AFs). During the production of bioethanol from maize, AF levels can increase up to three times in the final co-products, known as, dry and wet distiller's grain with solubles (DDGS and WDGS), intended for animal feed. Fungal enzymes like laccases can be a useful tool for reducing AF contamination in the co-products obtained from this process. The aim of the present study was to evaluate the ability of laccase enzymes included in enzymatic extracts (EE) produced by different species in the Basidiomycota phylum to reduce AF (AFB1 and AFB2) accumulation under the conditions of in vitro assays. Four laccase activities (5, 10, 15, and 20 U/mL) exerted by nine isolates were evaluated in the absence and presence of vanillic acid (VA), serving as a laccase redox mediator for the degradation of total AFs. The enzymatic stability in maize steep liquor (MSL) was confirmed after a 60 h incubation period. The most effective EE in terms of reducing AF content in the buffer was selected for an additional assay carried out under the same conditions using maize steep liquor obtained after the saccharification stage during the bioethanol production process. The highest degradation percentages were observed at 20 U/mL of laccase enzymatic activity and 1 mM of VA, corresponding to 26% for AFB1 and 26.6% for AFB2. The present study provides valuable data for the development of an efficient tool based on fungal laccases for preventing AF accumulation in the co-products of bioethanol produced from maize used for animal feed.
Assuntos
Aflatoxinas , Basidiomycota , Animais , Zea mays , Descontaminação , Lacase , Ácido VanílicoRESUMO
Maize (Zea mays L.) is an important crop in Argentina. Aspergillus flavus may infect this crop at growing stage and the harvested kernels can be contaminated with aflatoxins (AFs), whose levels may increase during storage. In Argentina, silo bags, a hermetic type of storage system, are widely used. Biocontrol based on competitive exclusion by atoxigenic A. flavus strains is a useful tool for AFs management at pre-harvest stage. The aim of the present study was to evaluate the effect of pre-harvest biocontrol treatments on aflatoxin B1 (AFB1) accumulation in maize stored in silo bags during 3 and 6 months. Three bioformulations based on A. flavus AFCHG2 and ARG5/30 strains were applied during field trials as single and mixed inocula. Harvested kernels were stored in non-hermetic and hermetic silo bags. At initial time (t0), 3 and 6 months (t3 and t6) the following parameters were evaluated: percentage of damaged kernels, moisture content, water activity, Aspergillus section Flavi incidence, relative humidity, O2 and CO2 levels into the silo bags, and AFB1 levels. The biocontrol strains included in the 3 bioformulations were able to infect maize kernels during the field trial and displaced native toxigenic isolates. At t0 control plots showed 10.9 ± 0.4 µg/kg of AFB1 while no AFs were detected in all the treatments. Along the storage assay AFB1 levels varied from not detected (<1 µg/kg) to 20.1 ± 0.8 µg/kg. Hermetic bags were better than non-hermetic bags in preventing AFB1 accumulation. Both single and mixed inocula were effective to control AFB1 accumulation in maize kernels during 3 and 6 months. AFB1 was not detected in kernels from the treatment at field stage with AFCHG2 + ARG5/30 after 6 months of storage into hermetic bags. The application of the biocontrol agents at field stage is an appropriate tool to reduce AFB1 accumulation under storage in hermetic silo bags. This is the first report on biocontrol strategy based on native atoxigenic strains applied at pre-harvest stage to reduce AFB1 accumulation during storage in Argentina.
Assuntos
Aflatoxinas , Aflatoxina B1 , Argentina , Aspergillus flavus , Zea maysRESUMO
Mycotoxins are secondary metabolites produced by fungal species that mainly belong to Aspergillus, Fusarium, Penicillium and Alternaria, which can grow in a variety of crops including cereals, oilseeds and fruits. Consequently, their prevalence in foods and by-products not only affects human and animal health but also causes important losses in both domestic and international markets. This review provides data about toxigenic fungal species and mycotoxin occurrence in different crops commonly grown in Argentina. This information will be relevant to establish adequate management strategies to reduce the impact of mycotoxins on human food and animal feed chains and to implement future legislation on the maximum permitted levels of these fungal metabolites.
Assuntos
Fusarium , Micotoxinas , Animais , Argentina , Contaminação de Alimentos/análise , Fungos , HumanosRESUMO
Aspergillus flavus is an opportunistic pathogen and may produce aflatoxins in maize, one of the most important crops in Argentina. A promising strategy to reduce aflatoxin accumulation is the biological control based on competitive exclusion. In order to select potential biocontrol agents among isolates from the maize growing region in Argentina, a total of 512 A. flavus strains were isolated from maize kernels and soil samples. Thirty-six per cent of the isolates from maize kernels did not produce detectable levels of aflatoxins, while 73% of the isolates from soil were characterized as non-aflatoxin producers. Forty percent and 49% of the isolates from maize kernels and soil samples, respectively, were not producers of cyclopiazonic acid (CPA). Sclerotia morphology was evaluated using Czapek Dox media. Eighty-six per cent of the isolates from maize kernels and 85% of the isolates from soil samples were L sclerotia morphotype (average diameterâ¯>â¯400⯵m). The remaining isolates did not produce sclerotia. All isolates had MAT 1-1 idiomorph. The competitive ability of 9 non aflatoxigenic strains, 4 CPA(+) and 5 CPA(-), was evaluated in co-inoculations of maize kernels with an aflatoxigenic strain. All evaluated strains significantly (pâ¯<â¯0.05) reduced aflatoxin contamination in maize kernels. The aflatoxin B1 (AFB1) reduction ranged from 6 to 60%. The strain A. flavus ARG5/30 isolated from maize kernels would be a good candidate as a potential biocontrol agent to be used in maize, since it was characterized as neither aflatoxin nor CPA producer, morphotype L, MAT 1-1 idiomorph, and reduced AFB1 content in maize kernels by 59%. This study showed the competitive ability of potential aflatoxin biocontrol agents to be evaluated under field trials in a maize agro-ecosystem in Argentina.
Assuntos
Antibiose/fisiologia , Aspergillus flavus/isolamento & purificação , Aspergillus flavus/metabolismo , Agentes de Controle Biológico/metabolismo , Zea mays/microbiologia , Aflatoxina B1/biossíntese , Argentina , Aspergillus flavus/classificação , Aspergillus flavus/patogenicidade , Produtos Agrícolas/microbiologia , Ecossistema , Indóis/metabolismo , Microbiologia do SoloRESUMO
Biological control is one of the most promising strategies for preventing aflatoxin contamination in peanuts at field stage. A population of 46 native Aspergillus flavus nonaflatoxin producers were analysed based on phenotypic, physiological and genetic characteristics. Thirty-three isolates were characterized as L strain morphotype, 3 isolates as S strain morphotype, and 10 isolates did not produce sclerotia. Only 11 of 46 non-aflatoxigenic isolates did not produce cyclopiazonic acid. The vegetative compatibility group (VCG) diversity index for the population was 0.37. For field trials we selected the non-aflatoxigenic A. flavus AR27, AR100G and AFCHG2 strains. The efficacy of single and mixed inocula as potential biocontrol agents in Northern Argentina was evaluated through a 2-year study (2014-2015). During the 2014 peanut growing season, most of the treatments reduced the incidence of aflatoxigenic strains in both soil and peanut kernel samples, and no aflatoxin was detected in kernels. During the 2015 growing season, there was a reduction of aflatoxigenic strains in kernel samples from the plots treated with the potential biocontrol agents. Reductions of aflatoxin contamination between 78.36% and 89.55% were observed in treated plots in comparison with the un-inoculated control plots. This study provides the first data on aflatoxin biocontrol based on competitive exclusion in the peanut growing region of Northern Argentina, and proposes bioproducts with potential use as biocontrol agents.