Effect of pH, water activity and temperature on the growth and accumulation of ochratoxin A produced by three strains of Aspergillus carbonarius isolated from Italian vineyards

Aspergillus carbonarius colonizes grapes and its derived products and produces ochratoxin A (OTA). In previous studies we screened 107 strains of A. carbonarius isolated from grapes for production of OTA, and we selected three high OTA-producing strains for this study (AC05, AC06, and AC07). The effect of different values of three conditions [temperature 15, 25, 30, 35°C; water activity (aw) 0.98, 0.95, 0.90, 0.88; and pH 4.0, 7.0, 9.0, 10.0] on A. carbonarius growth and OTA production was examined. A. carbonarius AC07 produced higher levels of OTA than AC06 and AC05 at all the variables tested. At 30°C the strains of A. carbonarius produced more OTA than at the other temperatures. A water activity of aw 0.98 produced the greatest mycelial growth and OTA accumulation for all three A. carbonarius strains. A pH of 4.0 produced the highest levels of OTA in all the strains. No growth was seen at aw 0.88 or at pH 10.0 in any strain, except AC07, which grew at pH 10.0. The optimal conditions for growth and production of OTA by A. carbonarius strains were 30°C, aw 0.98 and pH 4.0. When all the three factors (aw, pH, T) were combined, aw 0.98, pH 4.00 and 30ºC produced the highest levels of OTA in all the strains. Maximum amounts of OTA were found 7–9 days after inoculation in all the strains. Temperature, water activity, and pH had a great impact on OTA production by A. carbonarius and these factors should be taken into account when developing management practices for future research programmes.