RESUMO
BACKGROUND: Corn grains are commonly contaminated with mycotoxins and fungi. The purpose of this study was to evaluate the reduction of aflatoxins B1 , B2 , G1 , and G2 and the inhibition of Aspergillus niger in corn grains using ultrasound, ultraviolet (UV) radiation, electrolyzed water, and sodium bicarbonate. The determination of aflatoxins was performed by high-performance liquid chromatography with fluorescence detection and postcolumn derivatization, and analysis of A. niger was performed by evaluating mycelial growth in potato dextrose agar. The best treatment for reducing aflatoxins and inhibiting mycelial growth was evaluated in corn contaminated with A. niger. RESULTS: The results show a significant reduction in aflatoxins in the following order: sodium bicarbonate > ultrasound > UV > electrolyzed water for aflatoxins B1 , B2 , and G2 . For aflatoxin G1 , the order of reduction was sodium bicarbonate > ultrasound > electrolyzed water > UV, with maximum values between 70.50% and 87.03% reached with sodium bicarbonate; for the other treatments, the reduction was between 51.51% and 65.44%. Regarding the fungus, the order of inhibition in the control of mycelial growth was sodium bicarbonate > ultrasound > electrolyzed water > UV in corn grains, and inhibition of mycelial growth was obtained at a sodium bicarbonate concentration of 3.0 g L-1 . CONCLUSION: Sodium bicarbonate, electrolyzed water, ultrasound, and UV radiation inhibited the growth of A. niger on potato dextrose agar and reduced the contents of aflatoxins B1 , B2 , G1 , and G2 in vitro. Sodium bicarbonate showed an ability to inhibit mycelial growth in corn grains. © 2020 Society of Chemical Industry.
Assuntos
Aflatoxinas/química , Aspergillus niger/metabolismo , Conservação de Alimentos/métodos , Zea mays/química , Zea mays/microbiologia , Aflatoxinas/metabolismo , Aspergillus niger/efeitos dos fármacos , Aspergillus niger/efeitos da radiação , Conservação de Alimentos/instrumentação , Sementes/química , Sementes/microbiologia , Bicarbonato de Sódio/farmacologia , Ultrassom , Raios UltravioletaRESUMO
The enhanced thermal tolerance and survival responses of Escherichia coli O157:H7 in acid and acidified foods is a major safety concern for the production of low-pH products, including beverages. Little is known about this phenomenon when using UV light treatments. This study was conducted to evaluate the effects of strain (E. coli O157:H7 strains C7927, ATCC 35150, ATCC 43895, and ATCC 43889 and E. coli ATCC 25922) and physiological state (control-unadapted, acid adapted, and acid shocked) on the UV tolerance of E. coli in apple juice treated under conditions stipulated in current U.S. Food and Drug Administration regulations. A greater than 5-log reduction of E. coli was obtained under all tested conditions. A significant effect of strain (P < 0.05) was observed, but the physiological state did not influence pathogen inactivation (P ≥ 0.05). The UV sensitivity of three spoilage microorganisms (Aspergillus niger, Penicillium commune, and Alicyclobacillus acidoterrestris) was also determined at UV doses of 0 to 98 mJ/cm(2). Alicyclobacillus was the most UV sensitive, followed by Penicillium and Aspergillus. Because of the nonsignificant differences in UV sensitivity of E. coli in different physiological states, the use of an unadapted inoculum would be adequate to conduct challenge studies with the commercial UV unit used in this study at a UV dose of 14 mJ/cm(2). The high UV tolerance of spoilage microorganisms supports the need to use a hurdle approach (e.g., coupling of refrigeration, preservatives, and/or other technologies) to extend the shelf life of UV-treated beverages.
Assuntos
Alicyclobacillus/efeitos da radiação , Aspergillus niger/efeitos da radiação , Bebidas/microbiologia , Escherichia coli O157/efeitos da radiação , Malus/microbiologia , Penicillium/efeitos da radiação , Ácidos/metabolismo , Alicyclobacillus/crescimento & desenvolvimento , Aspergillus niger/crescimento & desenvolvimento , Bebidas/economia , Escherichia coli O157/metabolismo , Escherichia coli O157/fisiologia , Contaminação de Alimentos/análise , Irradiação de Alimentos , Malus/química , Penicillium/crescimento & desenvolvimento , Raios Ultravioleta , Estados UnidosRESUMO
The use of Aspergillus niger (A. niger) fungal spores as challenge organism for UV reactor validation studies is attractive due to their high UV-resistance and non-pathogenic nature. However A. niger spores UV dose-response was dependent upon sporulation conditions and did not follow the Bunsen-Roscoe Principle of time-dose reciprocity. Exposure to 8 h of natural sunlight for 10 consecutive days increased UV resistance when compared to spores grown solely in dark conditions. Application of 250 mJ cm(-2) at high irradiance (0.11 mW cm(-2)) resulted in a 2-log inactivation; however, at low irradiance (0.022 mW cm(-2)) a 1-log inactivation was achieved. In addition, surface electron microscopy (SEM) images revealed morphological changes between the control and UV exposed spores in contrast to other well accepted UV calibrated test organisms, which show no morphological difference with UV exposure.
Assuntos
Aspergillus niger/crescimento & desenvolvimento , Aspergillus niger/efeitos da radiação , Desinfecção/métodos , Esporos Fúngicos/crescimento & desenvolvimento , Esporos Fúngicos/efeitos da radiação , Raios Ultravioleta , Relação Dose-Resposta à Radiação , Esporos Fúngicos/ultraestruturaRESUMO
Plant cell wall is mainly composed by cellulose, hemicellulose and lignin. The heterogeneous structure and composition of the hemicellulose are key impediments to its depolymerization and subsequent use in fermentation processes. Thus, this study aimed to perform a screening of thermophilic and thermotolerant filamentous fungi collected from different regions of the São Paulo state, and analyze the production of β-xylosidase and arabinanase at different temperatures. These enzymes are important to cell wall degradation and synthesis of end products as xylose and arabinose, respectively, which are significant sugars to fermentation and ethanol production. A total of 12 fungal species were analyzed and 9 of them grew at 45 ºC, suggesting a thermophilic or thermotolerant character. Additionally Aspergillus thermomutatus anamorph of Neosartorya and A. parasiticus grew at 50 ºC. Aspergillus niger and Aspergillus thermomutatus were the filamentous fungi with the most expressive production of β-xylosidase and arabinanase, respectively. In general for most of the tested microorganisms, β-xylosidase and arabinanase activities from mycelial extract (intracellular form) were higher in cultures grown at high temperatures (35-40 ºC), while the correspondent extracellular activities were favorably secreted from cultures at 30 ºC. This study contributes to catalogue isolated fungi of the state of São Paulo, and these findings could be promising sources for thermophilic and thermotolerant microorganisms, which are industrially important due to their enzymes.
Assuntos
Aspergillus niger/enzimologia , Aspergillus niger/isolamento & purificação , Glicosídeo Hidrolases/análise , Neosartorya/enzimologia , Neosartorya/isolamento & purificação , Xilosidases/análise , Aspergillus niger/crescimento & desenvolvimento , Aspergillus niger/efeitos da radiação , Brasil , Programas de Rastreamento , Neosartorya/crescimento & desenvolvimento , Neosartorya/efeitos da radiação , TemperaturaRESUMO
Plant cell wall is mainly composed by cellulose, hemicellulose and lignin. The heterogeneous structure and composition of the hemicellulose are key impediments to its depolymerization and subsequent use in fermentation processes. Thus, this study aimed to perform a screening of thermophilic and thermotolerant filamentous fungi collected from different regions of the São Paulo state, and analyze the production of β-xylosidase and arabinanase at different temperatures. These enzymes are important to cell wall degradation and synthesis of end products as xylose and arabinose, respectively, which are significant sugars to fermentation and ethanol production. A total of 12 fungal species were analyzed and 9 of them grew at 45 ºC, suggesting a thermophilic or thermotolerant character. Additionally Aspergillus thermomutatus anamorph of Neosartorya and A. parasiticus grew at 50 ºC. Aspergillus niger and Aspergillus thermomutatus were the filamentous fungi with the most expressive production of β-xylosidase and arabinanase, respectively. In general for most of the tested microorganisms, β-xylosidase and arabinanase activities from mycelial extract (intracellular form) were higher in cultures grown at high temperatures (35-40 ºC), while the correspondent extracellular activities were favorably secreted from cultures at 30 ºC. This study contributes to catalogue isolated fungi of the state of São Paulo, and these findings could be promising sources for thermophilic and thermotolerant microorganisms, which are industrially important due to their enzymes.
Assuntos
Aspergillus niger/enzimologia , Aspergillus niger/isolamento & purificação , Glicosídeo Hidrolases/análise , Neosartorya/enzimologia , Neosartorya/isolamento & purificação , Xilosidases/análise , Aspergillus niger/crescimento & desenvolvimento , Aspergillus niger/efeitos da radiação , Brasil , Programas de Rastreamento , Neosartorya/crescimento & desenvolvimento , Neosartorya/efeitos da radiação , TemperaturaRESUMO
Plant cell wall is mainly composed by cellulose, hemicellulose and lignin. The heterogeneous structure and composition of the hemicellulose are key impediments to its depolymerization and subsequent use in fermentation processes. Thus, this study aimed to perform a screening of thermophilic and thermotolerant filamentous fungi collected from different regions of the São Paulo state, and analyze the production of ß-xylosidase and arabinanase at different temperatures. These enzymes are important to cell wall degradation and synthesis of end products as xylose and arabinose, respectively, which are significant sugars to fermentation and ethanol production. A total of 12 fungal species were analyzed and 9 of them grew at 45 °C, suggesting a thermophilic or thermotolerant character. Additionally Aspergillus thermomutatus anamorph of Neosartorya and A. parasiticus grew at 50 °C. Aspergillus niger and Aspergillus thermomutatus were the filamentous fungi with the most expressive production of ß-xylosidase and arabinanase, respectively. In general for most of the tested microorganisms, ß-xylosidase and arabinanase activities from mycelial extract (intracellular form) were higher in cultures grown at high temperatures (35-40 °C), while the correspondent extracellular activities were favorably secreted from cultures at 30 °C. This study contributes to catalogue isolated fungi of the state of São Paulo, and these findings could be promising sources for thermophilic and thermotolerant microorganisms, which are industrially important due to their enzymes.
Assuntos
Aspergillus niger/enzimologia , Aspergillus niger/isolamento & purificação , Glicosídeo Hidrolases/análise , Neosartorya/enzimologia , Neosartorya/isolamento & purificação , Xilosidases/análise , Aspergillus niger/crescimento & desenvolvimento , Aspergillus niger/efeitos da radiação , Brasil , Programas de Rastreamento , Neosartorya/crescimento & desenvolvimento , Neosartorya/efeitos da radiação , TemperaturaRESUMO
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.
Assuntos
Arachis/microbiologia , Aspergillus niger/metabolismo , Contaminação de Alimentos/análise , Irradiação de Alimentos , Ocratoxinas/biossíntese , Análise de Variância , Arachis/efeitos da radiação , Aspergillus niger/crescimento & desenvolvimento , Aspergillus niger/efeitos da radiação , Clima , Qualidade de Produtos para o Consumidor , Cinética , Fatores de Risco , Temperatura , Fatores de Tempo , Água/metabolismoRESUMO
Ochratoxin A (OTA) is one of the most important mycotoxins of worldwide concern for human health. The aims of this study were to evaluate the effects of water activity, temperature, incubation time and their interactions on growth, lag phase and OTA production by two strains belonging to A. niger aggregate in irradiated corn grains. This study shows that OTA production on corn grains occurs within a more restricted range of water activity and temperature than fungal growth. This point is important in order to maintain the appropriate conditions in stored corn that prevent toxigenic fungal growth and thus OTA production. Irradiated corn grains were re-hydrated to 0.910-0.995 of a(W) with sterile distillate water. The temperatures assayed were 15, 25 and 30 degrees C. Growth assessment was made every day during the incubation period (21 days) to calculate the growth rate, lag phase and the OTA production at 7, 14 and 21 days. Both strains showed optimum growth at 30 degrees C at 0.951 a(W). Ochratoxin A production occurred over a range of temperatures (15-30 degrees C) with optimum production at 25 degrees C depending on a(W) assayed. Maximum OTA production was obtained for both strains at 0.973 a(W). The results obtained suggest that the storage of corn grains at water activities lower than 0.951 and 15 degrees C should prevent these fungal species growth and OTA production during 21 days approximately.
Assuntos
Aspergillus niger/crescimento & desenvolvimento , Irradiação de Alimentos , Conservação de Alimentos/métodos , Ocratoxinas/biossíntese , Zea mays/microbiologia , Aspergillus niger/metabolismo , Aspergillus niger/efeitos da radiação , Contagem de Colônia Microbiana , Qualidade de Produtos para o Consumidor , Contaminação de Alimentos/análise , Contaminação de Alimentos/prevenção & controle , Humanos , Cinética , Temperatura , Fatores de Tempo , Água/metabolismo , Zea mays/efeitos da radiaçãoRESUMO
Mutant strains from Aspergillus niger UAM-GS1 were produced by UV radiation to increase their hemicellulolytic and cellulolytic activity production. The mutant strains showing more enzymatic activity were those labelled GS1-S059 and GS1-S067. These strains also showed the largest relationship between diameter of hydrolysis zone and colony diameter. The mutant GS1-S067 showed a colony radial extension rate and a biomass growth rate g biomass/(cm² h), 1.17 times higher than that achieved by strain UAM-GS1. The high invasive capacity makes this mutant strain a promising alternative for its use in solid substrate fermentation (SSF). The morphological properties of the two mutant strains were evaluated by using scanning electron microscopy. The diameter of the sporangium of the mutant strains GS1-S059 and GS1-S067 was significantly larger (P < 0.05) than that found for the parental strain. The hypha length and diameter of the mutant strains significantly changed (P < 0.05) compared to the parental strain. A Pearson correlation analysis on hypha length, sporangium diameter, and cellulase and xylanase activities indicated that there was a strong relationship among these variables in relation to mannanase activity. Mutant strains GS1-S059 and GS1-S067 significantly increased their level of mannanase, xylanase and cellulase production, compared to the parental strain, improving their potential industrial applications.
Assuntos
Aspergillus niger/enzimologia , Aspergillus niger/genética , beta-Manosidase/biossíntese , Aspergillus niger/crescimento & desenvolvimento , Aspergillus niger/efeitos da radiação , Aspergillus niger/ultraestrutura , Celulase/biossíntese , /biossíntese , Microscopia Eletrônica de Varredura , Mutação , Raios Ultravioleta , beta-Manosidase/metabolismoRESUMO
Spores of Bacillus subtilis, conidia of Aspergillus niger, versicolor and ochraceus and cells of Deinococcus radiodurans have been exposed in the dark at two locations (at about 23 degrees S and 24 degrees S) in the Atacama Desert for up to 15 months. B. subtilis spores (survival approximately 15%) and A. niger conidia (survival approximately 30%) outlived the other species. The survival of the conidia and spores species was only slightly poorer than that of the corresponding laboratory controls. However, the Deinococcus radiodurans cells did not survive the desert exposure, because they are readily inactivated at relative humidities between 40 and 80% which typically occur during desert nights. Cellular monolayers of the dry spores and conidia have in addition been exposed to the full sun light for up to several hours. The solar fluences causing 63% loss in viability (F37-values) have been determined. These F37-values are compared with those determined at other global locations such as Punta Arenas (53 degrees S), Key Largo (25 degrees N) or Mainz (50 degrees N) during the same season. The solar UVB radiation kills even the most resistant microorganisms within a few hours due to DNA damages. The data are also discussed with respect to possible similarities between the climatic conditions of the recent Atacama Desert and the deserts of early Mars.