Influence of water activity on Penicillium citrinum growth and kinetics of citrinin accumulation in wheat.

The influence of water activity (aw) on both Penicillium citrinum growth and citrinin accumulation in wheat was studied. Wheat conditioned at different levels of aw and inoculated with a citrinin producer strain was incubated at 30 degrees C for 2 months. Fungal growth was assessed by microscopic examination. P. citrinum grew down to aw 0.775. Citrinin was not detected in the substrate at aw 0.800 and lower. As aw increased the toxin was detected earlier and the maximum accumulation increased markedly (65 microg/kg at aw 0.810, 460 microg/kg at aw 0.825 and 22 mg/kg at aw 0.885). Citrinin concentration declines rapidly after reaching the maximum at each aw level.