Effect of gamma radiation on morphology and toxigenic capacity of Aspergillus strains.

RIBEIRO J.M.M.,; FRAGA M., .; MAGNOLI C.,; FERNANDEZ J.M.G.,; DALCERO A.M.,; ROSA C.A.R

Nantes, Aperdpa Francia

Congreso; 10th Congress of the European Society of Veterinary and Comparative Nutrition, Congress Proceedings.; 2006

The ability of ionizing radiation to kill microorganisms has been investigated since the late 19th century. The industrial application of ionizing energy for preservation of foods for man and animals has been reviewed by several workers. The mycotoxin contamination in grain is difficult to predict because it depends on complex interactions of factors such as temperature, moisture, endogenous fungal species and storage history and time. The enhancement of production of mycotoxins resulting from gamma irradiation has been raised. The aims of this work were evaluate the effect of various doses of gamma irradiation on the growth characteristics and the mycotoxins production by A. parasiticus, A. ochraceus and A. niger on Czapek yeast extract agar. The strains used were: A. niger 0437, A. nigeri Pc 0437, A. ochraceus NRRL 3174, A. parasiticus 0335, A. parasiticus 0336, A. parasiticus S 0336. Erlenmeyer flasks (500 ml) containing 150 g sterile corn (aW 0.90) were inoculated with 106 spores ml-1 of each fungal strain and incubated during 3 days at 28°C. Then, they were irradiated with 0, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 and 5.0 kGy in air with a 137Cs irradiation unit (Centro do Exército – CTEx. Guaratiba, Río de Janeiro, Brasil). Macroscopic and microscopic aspects of Aspergillus strains after irradiation were evaluated in extract malt agar (MEA), Czapek yeast extract agar (CYA) incubated at 28 and 37ºC during 7 days, following the keys proposed by Klich (2002). Their ability to produce aflatoxins was evaluated in extract malt agar according to the methodology proposed Geisen (1996), the extraction of toxins was made with chloroform and detection by TLC and confirmed by HPLC method. There were many changes in the morphological characteristics between control and irradiated strains and such as: color, texture and reverse of colonies, pigment production, color, size and aspect of conidia. The strain A. parasiticus 0336 control produced 8.5 mg/g of mycelium, these strains and A. parasiticus S 0336 irradiated with 2.5 kGy produced higher levels of toxin, 23 and 17mg/g, respectively. These results suggest that the irradiation methodology used to diminish or eliminate the microbial infection on foods and feeds could modify the genetic characteristics of toxigenics fungi and could increase the mycotoxins production.