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

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