Water activity and temperature effects on growth of Aspergillus niger, A. awamori and A. carbonarius isolated from different substrates in Argentina.

The objectives of this study were to determine the effect of water activity, temperature, and their interactions on a) mycelial growth rate and b) the lag phase prior to grow of seven isolates of Aspergillus section Nigri isolated from peanuts, maize kernels, dried grapes and coffee cherries from Argentina. Three Aspergillus niger, three A. awamori and one A. carbonarius isolates examined showed optimum a(W) level for growth at 0.97 with optimal temperature of 30 degrees C. for most of the isolates and 25 degrees C for only one (A. awamori RCP176). Minimal a(W) for growth was 0.85 at the highest temperature tested. Overall growth was reduced up to 50% at 0.93 a(W). Growth was also to a large extend inhibited at 0.85 a(W) for most isolates even after 21 days of incubation at temperatures lower than 30 degrees C. The analysis of variance of the effect of single (isolate, a(W) and temperature), two- and three-way interaction showed that all factors alone and all interactions were statistically significant (P<0.001) in relation to growth rates and lag phase for A. niger, A. awamori and A. carbonarius isolates. These data are relevant since these species are isolated in high frequency on numerous substrates for human and animal consumption in Argentina.