[Comparison of the effects of heat and radiation on Aspergillus parasiticus]

The inactivation effect and fungus toxin production of Aspergillus parasiticus NRRL 2999 were studied by means of ionizing radiations. The dose-survival curve reveals two different responses to radiation: the first one, showing a relatively high sensitivity, corresponds to mycelia; the second one, more resistant, to non-germinated conidiospores with a D10 value of 0.77 kGy. To carry on further experiments, 1.5 kGy was chosen as radiation treatment dose, which is twice the D10 value for the most resistant form. The mould was cultivated on rice, under ideal temperature and humidity conditions, so as to assure toxin production. Samples of different ages were irradiated, and 20 hour old mycelium turned out to be the most susceptible to radiation damage. Therefore 20 hours after inoculation, the following experiments were performed: a) irradiation; b) heating; c) heating followed by irradiation. Aflatoxin production was measured along 11 days of incubation, by dilution to extinction on thin layer chromatography. Results obtained show that heated or irradiated samples have decreased aflatoxin levels compared to controls, and the combined treatment reduce them below the detection limit of our analytical method, and also below the maximum levels advised by the international organizations on health (FAO/OMS, 1966: less than 30 ppb).