Water activity and temperature effects on mycotoxin production by Alternaria alternata on a synthetic tomato medium

Alternaria spp. have been reported to be the most frequent fungal species invading tomatoes. Certain species, in particular the most common one, A. alternata, are capable of producing several mycotoxins in infected plants and in agricultural commodities. Alternariol (AOH), alternariol monomethyl ether (AME), and tenuazonic acid (TA) are some of the main Alternaria mycotoxins that can be found as contaminants of food. The objective of this study was to determine the effect of water activity (aw, 0.904, 0.922, 0.954, and 0.982) and temperature (6, 15, 21 and 35°C) on mycotoxin production on a synthetic tomato medium of a cocktail inoculum of five strains of A. alternata isolated from tomato fruits affected by Blackmould. The optimum AOH production occurred at 0.954 aw after 28days of incubation at 21°C. A temperature of 21°C was the most favourable for AOH synthesis at all aw levels. The maximum concentration of AME was determined at 0.954 aw and 35°C. The optimum conditions for TA accumulation were 0.982 aw and 21°C. At the 0.904 aw no growth or germination was registered at 6°C and 15°C over the whole incubation period. At 21°C and 35°C growth occurred slowly but none of the toxins were detected at this aw level. In general, high aw levels were favourable for mycotoxin production. None of the other toxins was detected at quantifiable levels at 6°C after the whole incubation period. A storage temperature of 6°C or below could be considered as safe for tomato fruits and high moisture tomato products (aw>0.95), in relation with Alternaria toxins. The results obtained here could be extrapolated to evaluate the risk of spoilage in tomato fruits and tomato products caused by this pathogen.Fil: Pose, Graciela Noemi. Universidad Nacional de Quilmes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Patriarca, Andrea Rosana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Orgánica; ArgentinaFil: Kyanko, V.. Universidad Nacional de Quilmes; ArgentinaFil: Pardo, Alejandro Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Fernández Pinto, Virginia Elena. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Orgánica; Argentin

β-Glucan content and hydration properties of filamentous fungi

The aim of this work was to isolate and identify filamentous fungi from several sources to study the dietary fiber and β-glucan content. The fungal hydration properties such as water absorption and water holding capacities were also evaluated. Total dietary fiber of isolates exhibited a noticeable variability from 16 to 53% and the highest values were obtained for the genera Paecilomyces and Penicillium, a fact consistent with a higher content of β-glucans (24 and 17%, respectively), higher than previously reported for Basidiomycetes and yeast. We observed a large decrease (75%) in the water holding capacity when the mycelia were dried. Isolates of filamentous fungi with greater water holding capacity also exhibited greater absorption capacity. Paecilomyces variotii and Penicillium nalgiovense had the best hydration properties. Our results contribute to the search for new unconventional ingredients providing a high protein and β-glucans content. The addition of these dried mycelia could change the hydration properties in the food system.Fil: Kyanko, M. V.. Universidad Nacional de Quilmes; ArgentinaFil: Canel, Romina Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ludemann, Vanesa. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Pose, Graciela Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Wagner, Jorge Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Effect of water activity and temperature on growth of Alternaria alternata on a synthetic tomato medium

Alternaria alternata is a toxigenic fungus, predominantly responsible for Blackmould of ripe tomato fruits, a disease frequently causing substantial losses of tomatoes, especially those used for canning. The objective of this study was to determine the effect of water activity (aw, 0.904, 0.922, 0.954, 0.982) and temperature (6, 15, 21 and 35 °C) on germination and radial growth rate on a synthetic tomato medium of a cocktail inoculum of five strains of A. alternata isolated from tomato fruits affected by Blackmould. The shortest germination time (1.5 days) was observed at 0.982 aw, both at 21 °C and 35 °C. The germination time increased with a reduction on aw. The fastest growth rate was registered at 0.982 aw and 21 °C (8.31 mm/day). Growth rates were higher when aw increased. No growth or germination was observed at the lowest aw level evaluated (0.904) after 100 days of incubation at 6 °C and 15 °C. A temperature of 6 °C caused a significant reduction in growth rates, even at the optimum aw level. The knowledge on the ecophysiology of the fungus in this substrate is necessary to elaborate future strategies to prevent its development and evaluate the consumer health risk.Fil: Pose, Graciela Noemi. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Micología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Patriarca, Andrea Rosana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Micología y Botánica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Micología y Botánica; ArgentinaFil: Kyanko, María V.. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Micología Molecular; ArgentinaFil: Pardo, Alejandro Guillermo. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Micología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Fernández Pinto, Virginia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Micología y Botánica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Micología y Botánica; Argentin