Modelling of the individual and combined effects of water activity and temperature on the radial growth of Aspergillus flavus and A. parasiticus on corn

A full factorial design of five temperatures (16, 22, 25, 30 and 37 °C) and seven aw values between 0.801 and 0.982 was used to investigate the growth of the two major aflatoxin producing Aspergillus isolates on corn. The colony growth rates (g, mm d−1) and lag phases (λ, d) were estimated by fitting a flexible primary growth model. Subsequently, secondary models relating g or λ to aw or temperature or aw and temperature combined, were developed and validated by using independently collected data. The Gibson and linear Arrhenius–Davey model describing the individual effects of aw or temperature on g or λ proved an adequate predictor of either growth parameter. Based on the validation criteria, a quadratic polynomial function proved to be more suitable than a Gaussian function or extended Davey model for describing the combined effect of aw and temperature on g or λ. Both isolates studied had optimum growth temperatures of approximately 30 °C. No growth was observed for both isolates at aw 0.801, growth only occurring at 25 and 30 °C at aw 0.822. Significant interaction between aw and temperature on g and λ was observed for both isolates. The developed models can be applied in the preservation of corn and the development of models that incorporate other factors important to mould growth on corn.