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AIMS: The aims of this article were to select fungal species with high tolerance and high growth rate in mediums supplemented with limonene and citrus essential oils (CEOs), and to test the bioconversion capability of the chosen isolates for the bioproduction of aroma compounds. METHODS AND RESULTS: Based on the use of predictive mycology, 21 of 29 isolates were selected after assaying R-(+)-limonene and CEO tolerance (10 g l-1 ). With a dendrogram divisive coefficient of 0·937, the subcluster two with isolates Aspergillus niger LBM 055, Penicillium sp. LBM 150, Penicillium sp. LBM 151 and Penicillium sp. LBM 154 gathered the highest tolerance and mycelia growth speed. Ultrastructural analysis indicated that culture media containing limonene had no visible toxic activity that could promote morphological changes in the fungal cell wall. The biomass of A. niger LBM055 was distinctive in liquid media supplemented with R-(+)-limonene (0·57 ± 0·07 g) and it was selected to prove bioconversion capacity, under static and agitated conditions, and converted up to 98% of limonene, yielding a wide variety of products that were quantified by GC-FID. It was obtained at molecular weights less than limonene (64-100%), between limonene and α-terpineol (12-72%) and greater than α-terpineol (2-48%). CONCLUSIONS: Aspergillus niger LBM 055, Penicillium sp. LBM 150, Penicillium sp. LBM 151 and Penicillium sp. LBM 154 showed to the highest tolerance and growth rate in mediums supplemented with R-(+)-limonene and orange and lemon essential oils. Particularly, A. niger LBM055, showed limonene bioconversion capability and produced different molecular weights compounds such us α-terpineol. SIGNIFICANCE AND IMPACT OF THE STUDY: Different bioproducts can be obtained by changing operative condition with the same fungus, and this bioprocess aspect is a significant approach to be adopted on industrial scale leading to the creation of new natural flavours and fragrance compositions.

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Fungal spoilage in fruit juices is a currently relevant issue considering that recent reports have found unacceptable fungal levels even after traditional pasteurization processes. Ohmic heating demonstrated to be a good alternative process to conventional pasteurization, as it can promote higher heating rates and additional cell damage in some scenarios (nonthermal effects). However, the application of ohmic processing for fungi inactivation has not been properly investigated. The objective of this study was to analyze the inactivation of Aspergillus fumigatus, a highly distributed fungi species, in apple juice by ohmic and conventional heating at 75, 80, 85, 90 and 94 °C. Predictive primary and secondary models were fitted and the Weibull-Mafart models were the most accurate to describe the experimental behavior considering the statistical indices applied. Statistical differences between both thermal processes were found in the three lower analyzed temperatures (75, 80 and 85 °C), which is possibly related to nonthermal effects. When ohmic heating was applied, processing time was up to 23% shorter. The resulted model was successfully validated in two distinct temperatures (83 and 92 °C) and could be applied to obtain adequate processing times for apple juice pasteurization. This study contributes to deepen the knowledge concerning the use of ohmic heating for fungi inactivation.

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This study aimed to model the aflatoxin B1 (AFB1) production by A. flavus in wheat grains during malting for craft beer. A total of sixty-four different combinations of grains steeping degree (ST; 41, 43, 45 and 47%), temperature (13, 15, 17 and 19 °C) and time of germination (48, 72, 96 and 120 h), comprising the range of malting conditions that allow the production of quality malt, were assayed. AFB1 was produced in a range of 15.78 ± 3.54 µg/kg (41% ST, 13 °C for 48 h) to 284.66 ± 44.34 µg/kg (47% ST, 19 °C for 120 h). The regression model showing an acceptable fit to the experimental data (adjusted R2 0.84) for AFB1 as a function of grains steeping degree, temperature and time of germination. Results showed that AFB1 levels in wheat malt increase with increase of the temperature or time of germination. Within the range of tested malting conditions, no significant effects were observed for steeping degree on AFB1 levels in wheat malt. The generated model is useful to estimate the AFB1 levels in wheat malt. Findings highlight overall that if wheat grains are contaminated with A. flavus, AFB1 might be produced in malt in levels above the limits set by regulatory agencies, regardless the steeping conditions used.

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Yeasts are able to reduce the levels of ochratoxin A in fermentative processes; and, through their enzymatic complex, these micro-organisms are also capable of forming modified mycotoxins. These mycotoxins are often underreported, and may increase health risks after ingestion of contaminated food. In this sense, this study aims to evaluate whether the presence of ochratoxin A influences yeast growth kinetic parameters and to elucidate the formation of modified ochratoxin by Saccharomyces cerevisiae strains during fermentation. Three S. cerevisiae strains (12 M, 01 PP, 41 PP) were exposed to OTA at the concentrations of 10, 20 and 30 µg/L. The Baranyi model was fitted to the growth data (Log CFU/mL), and the identification of modified ochratoxins was performed through High Resolution Mass Spectrometry. The presence of ochratoxin A did not influence the growth of S. cerevisiae strains. Four pathways were proposed for the metabolization of OTA: dechlorination, hydrolysis, hydroxylation, and conjugation. Among the elected targets, the following were identified: ochratoxin α, ochratoxin ß, ochratoxin α methyl ester, ochratoxin B methyl ester, ethylamide ochratoxin A, ochratoxin C, hydroxy-ochratoxin A, hydroxy-ochratoxin A methyl ester, and ochratoxin A cellobiose ester. These derivatives formed from yeast metabolism may contribute to the occurrence of underreporting levels of total mycotoxin in fermented products.

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The aim of the present study was to assess the ability of different white-rot fungi to tolerate polychlorinated biphenyls (PCBs) using predictive mycology, by relating fungal growth inhibition to ligninolityc enzyme secretion. Fungal strains were grown in the presence of PCBs in solid media and their radial growth values were modelled through the Dantigny-logistic like function in order to estimate the time required by the fungal colonies to attain half their maximum diameter. The principal component analysis (PCA) revealed an inverse correlation between strain tolerance to PCBs and the laccase secretion over time, being laccase production closely associated with fungal growth capacity. Finally, a PCA was run to regroup and split between resistant and sensitive fungi. Simultaneously, a function associated with a model predicting the tolerance to PCBs was developed. Some of the assayed isolates showed a promising capacity to be applied in PCB bioremediation. Abbreviations: Polychlorinated biphenyls (PCBs), white-rot fungi (WRF).

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AIMS: The aim of this work was to use mathematical kinetic modelling to assess the combined effects of aW, pH, O2 availability and temperature on the growth rate and time to growth of Aspergillus fumigatus strains isolated from corn silage. METHODS AND RESULTS: A full factorial design was used in which two factors were assayed: pH and aW . The aW levels assayed were 0·80, 0·85, 0·90, 0·92, 0·94, 0·96, 0·98 and 0·99. The levels of pH assayed were 3·5, 4, 4·5, 5, 6, 7, 7·5 and 8. The assay was performed at normal oxygen tension at 25 and 37°C, and at reduced oxygen tension at 25°C. Two strains of A. fumigatus isolated from corn silage were used. Kinetic models were built to predict growth of the strain under the assayed conditions. The cardinal models gave a good quality fit for radial growth rate data. The results indicate that the environmental conditions which take place during silage production, while limiting the growth of most micro-organisms, would not be able to control A. fumigatus. Moreover, pH levels in silage, far from limiting its growth, are also close to its optimum. Carbon dioxide at 5% in the environment did not significantly affect its growth. CONCLUSIONS: A need for a further and controlled acidification of the silage exists, as no growth of A. fumigatus was observed at pH 3·5, as long as the organoleptic characteristics of the silage are not much compromised. SIGNIFICANCE AND IMPACT OF THE STUDY: Aspergillus fumigatus is one of the major opportunistic pathogens able to cause illness such as allergic bronchopulmonary aspergillosis, aspergilloma and invasive aspergillosis to rural workers. Exposure of animals to A. fumigatus spores can result in infections, particularly in those organs exposed to external invasion, such as the airways, mammary gland and uterus at birth.

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The aim of this study was to establish primary and secondary models to describe the growth kinetics of Byssochlamys fulva on solidified apple juice at different temperatures. B. fulva was inoculated on solidified apple juice at 10, 15, 20, 25 and 30 °C. Linear-with-breakpoint, Baranyi and Roberts, and Huang primary models (without upper asymptote) were fitted to the data, and they showed good ability to describe the growth kinetics. B. fulva showed longer adaptation time on apple juice than on culture medium, but growth rates were similar as reported in the literature. The dependence of µmax and λ parameters on temperature was described with Square Root and Arrhenius-Davey secondary models, respectively. These models were important to establish process/storage conditions and apple juice shelf life.