100A-10

Using a Box Behnken experimental design, the combined effect of water activity (0.990, 0.945, 0.900) and pH (5.5, 4.5, 3.5) reduction, and the simultaneous application of selected atmospheric compositions (3, 6, 9%O₂ with 15%CO₂ and N₂) on Aspergillus flavus and A. parasiticus growth response during 30 days incubation period at 25ºC were evaluated.

The a_w-adjusted agar was sterilized, cooled, and pH adjusted with citric acid. Triplicate plates of every combination of factors tested were centrally inoculated with a mold spore suspension and incubated for one month over NaCl solutions of the same a_w in incubation chambers with the corresponding modified atmospheric composition. The inoculated systems were microscopically observed every day and the colony diameter was recorded.

An atmosphere with 9% O₂ had little effect on mold growth, similar colony diameters were obtained in this system and in the control (air). In general, a reduction in O₂ levels retarded mycelial growth. Both molds were inhibited when combining a_w 0.90, at pH 3.5, and 3% O₂. An analysis of variance demonstrated that the individual and combined effects of the evaluated factors have a significant (p<0.05) effect on mold colony diameter, radial growth rate and on lag phase. Polynomial equations were generated to describe and predict mold growth resposes, demonstrating the significant effect of independent variables as well as selected interactions. In general, A. flavus was more sensible to changes on the atmosphere composition than A. parasiticus.

Combination of stress factors including atmosphere modification can effectively control mold growth. Synergistic interactions may be used to avoid fungal spoilage in selected food products.