Impact of some environmental factors on growth and production of ochratoxin A of/by Aspergillus tubingensis, A. niger, and A. carbonarius isolated from Moroccan grapes.

The effects of temperature, water activity (aw), incubation time, and their combinations on radial growth and ochratoxin A (OTA) production of/by eight Aspergillus niger aggregate strains (six A. tubingensis and two A. niger) and four A. carbonarius isolated from Moroccan grapes were studied. Optimal conditions for the growth of most studied strains were shown to be at 25 degrees C and 0.95 aw. No growth was observed at 10 degrees C regardless of the water activity and isolates. The optimal temperature for OTA production was in the range of 25 degrees C-30 degrees C for A. carbonarius and 30 degrees C-37 degrees C for A. niger aggregate. The optimal aw for toxin production was 0.95-0.99 for A. carbonarius and 0.90-0.95 for A. niger aggregate. Mean OTA concentration produced by all the isolates of A. niger aggregate tested at all sampling times shows that maximum amount of OTA (0.24 microg/g) was produced at 37 degrees C and 0.90 aw. However, for A. carbonarius, mean maximum amounts of OTA (0.22 microg/g) were observed at 25 degrees C and 0.99 aw. Analysis of variance showed that the effects of all single factors (aw, isolate, temperature and incubation time) and their interactions on growth and OTA production were highly significant.