Ochratoxin A production by a mixed inoculum of Aspergillus carbonarius at different conditions of water activity and temperature

Growth rate, lag phase and OTA production of a mixed inoculum of four Aspergillus carbonarius strains were compared to the behaviour of the single strains at 30 °C on Czapek Yeast Extract Agar. Significant differences between radial growth rates and lag phases of the different isolates were observed; however, no significant differences between growth rates of each strain and the mixed inoculum were detected. When the four strains were inoculated simultaneously, the lag phase was the same than the higher value obtained for individual strains, suggesting mycelial interactions between the A. carbonarius isolates. The four strains differed in maximum OTA yield, and the toxin accumulation by the mixed inoculum showed intermediate levels at each time point. The effects of water activity (0.83, 0.85, 0.87, 0.89, 0.90, 0.93 and 0.95) and temperature (15, 20, 25, 30, and 35 °C) on OTA production by the mixed inoculum were studied at 7, 14, 21 and 28 days of incubation. The limiting water activity for OTA production by the mixed inoculum was 0.87, showing xerotolerant behaviour of the strains isolated from dried vine fruits. Results obtained were similar to those reported for single A. carbonarius strains from European countries, Israel, Australia and South America. The similar trend in the response of the different isolates to the variation of environmental parameters may be of interest for the building of predictive models.