Influence of water activity on deoxynivalenol accumulation in wheat

The influence of water activity (a_w) on deoxynivalenol accumulation in wheat at 25°C was studied. Gnotobiotic grains were conditioned at different a_w levels, inoculated with a toxigenic Fusarium graminearum strain, and incubated for ten weeks. The highest accumulation of deoxynivalenol (1130 ug/kg) was detected at a_w 0.980. At a_w 0.945 and 0.925 the maximum quantities of toxin accumulated were 113 ug/kg and 93 ug/kg respectively. Deoxynivalenol was not detected in the substrate at a_w 0.900. Results suggest that intermediate a_w levels (0.97 – 0.92) are particularly critical at post harvest time because those are conditions under which deoxynivalenol production is most likely to be initiated naturally.