Aspergillus carbonarius growth and ochratoxin A production on irradiated dried grapes under different water activity and temperature conditions

Grapes have different destinations. The most important in the national and international market is wine production, but another is dehydration to produce raisins. Dried vine fruits are at greater risk of ochratoxin A (OTA) contamination than wine grapes because the ratio of Aspergillus carbonarius to Aspergillus niger aggregate increases during drying. The growth of these species, and consequently OTA production, can be influenced by different environmental factors, the two most important being water activity (a(w)) and temperature. The objective of the present work was to evaluate the lag phase, growth rate and OTA production by two A. carbonarius isolates on irradiated dried grapes at different a(w) (0.910, 0.928, 0.955, 0.973 and 0.995), temperatures (15, 25 and 30 degrees C) and incubation times (7, 14 and 21 days). Growth was observed at all aw and temperature ranges assayed. No significant differences between the growth rates reached at 25 degrees C and 30 degrees C by both isolates were observed. At the assayed conditions, OTA production occurred over the whole range of temperatures (15-30 degrees C), with the maximum at 25 and 30 degrees C depending on the aw. In general, OTA concentration increased as a(w) increased with no statistically significant differences at the tested incubation times. This work provides information that can be used by companies for the purpose of preventing A. carbonarius and OTA contamination during storage on this and other substrates (e.g. dried prunes, figs and apricots) destined for human consumption.