Effect of culture medium, temperature and incubation time on growth and ochratoxin A production by Aspergillus tubingensis and A. niger isolated from Moroccan vineyards

Abstract

The effects of culture media (YES, CYA, SNM), temperature (10, 15, 20, 25, 30 and 37°C), incubation time (5, 10, 15 and 20 days) and their interactions on radial growth and OTA production by six A. tubingensis and two A. niger were studied. Growth rate increased as temperature increased, regardless of the culture media and isolates. Total inhibition of fungal growth of all strains on the three culture media was observed at 10°C. Mean growth rates calcu-lated for A. niger (2 isolates) and A. tubingensis (6 isolates) revealed that optimal temperatures for growth were observed at 30-37°C on CYA and YES media with maximal growth rates of 5.7 and 5.4 mm/day for A. niger and A. tubingensis cultivated in YES medium, respectively. Growth on SNM medium is generally slow, regardless the temperature and strain used. For both spe-cies, maximum means growth rates were determined at 37°C (3.7-3.8 mm/day). For OTA production, an incubation period of 5 days is sufficient to de-tect the OTA. Levels of this toxin are dependent on temperature, incubation time and strain. In the A. tubingensis specie, maximum of 0.710 μg/g of OTA was obtained after 10 days of incubation at 25°C on SNM medium while for A. niger, the maximum (0.36 μg/g) was obtained on CYA medium. The opti-mum conditions for OTA production are 25 °C/10 days. Analysis of variance showed that the effects of single factors (culture medium, temperature, in-cubation time and strain) and their interactions on growth and OTA produc-tion were highly significant (P=0.000).