Mycelial discs of the fungus Aspergillus ochraceus NRRL 3174 were exposed to gamma irradiation and then incubated on synthetic medium (SM). Growth rate, mycelial dry weight and ochratoxin production were measured. A delay in mycelial growth of 24 and 48h over the control occurred following irradiation of mycelial discs with 150 and 200 krad, respectively. No growth occurred from discs exposed to 300 krad. An increase in ochratoxin production occurred on the SM from cultures developing from discs of mycelium which had been irradiated with 50, 100, 150 and 200 krad. The amount of toxin produced was 3500, 4100, 3200 and 3000 ng per plate, respectively, as compared with 2800 ng per plate produced by the control. Exposure of mycelial discs to a temperature of 40°C for 15 and 30 min prior to treatment with 200 krad resulted in complete inhibition in mycelial growth. No growth inhibition or notable change in ochratoxin production was recorded when the mycelial discs were exposed to 25, 50 or 100 krad after the heat treatments. Pure ochratoxin was found to be stable even at 7.5 mrad, and no reduction in its fluorescence intensity under u. v. light was recorded following that dose.

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The effect of gamma irradiation of whole-corn grains on mold development during storage and on nutritional value for broiler chicks was determined in two experiments. Moisture content (MC) of the grains was either ca. 13.5 (natural) or ca. 16% (moistened); irradiation was applied at dosages of 7 and 10 kUogray (kGy) with follow-up of fungal development during the next 80 and 96 days. Feeding tests were initiated after 120 and 173 days of storage in Experiments 1 and 2, respectively.Mold development was observed already after 11 days in moistened grains. Irradiation, particularly of grains with low MC, delayed, but did not prevent fungal development. Fat content of moistened grains at the end of the storage period was not changed in Experiment 1, but it decreased markedly in Experiment 2. Irradiation did not affect this variable.The moistened corn did not adversely affect chick performance in Experiment 1, whereas in Experiment 2 it significantly (P<0S) increased feed intake and weight gain and depressed feed efficiency. Irradiation did not affect either of the variables of chick performance.It was concluded that gamma irradiation at the dosages applied was effective in preventing moldiness of low MC corn grains for ca. 60 days. However, moldiness per se did not necessarily disqualify the grains for use in poultry nutrition. Before use, such grains should be analyzed for the presence of mycotoxins, and their fat content determined to ensure their safety and economical value. (

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Tryptic soy broth/agar, brain heart infusion agar and Columbia broth/agar, all widely used in the bacteriological laboratory, were radiation‐sterilized at a dose of 10–15 kGy. The media were tested for the growth of 12 different micro‐organisms, including fastidious pathogens such as Streptococcus pyogenes, Strep, pneumonias, Haemophilus influenzas and Neisseria meningitidis. Solid and fluid media supplemented with catalase before irradiation performed well in comparison with heat‐sterilized media.