Amaranth grain as substrate for aflatoxin and zearalenone production at different water activity levels

The influence of water activity ( a w) on the kinetics of aflatoxin and zearalenone production in amaranth grains at 25°C was studied. Minimum a w for aflatoxin production in this substrate was 0.825. Accumulation of the four aflatoxins (B 1, B 2, G 1 and G 2) was similar at a w 0.825 (maximum 81.2 μg/kg after 42 days) and 0.868 (maximum 109.6 μg/kg after 49 days). Maximum accumulation of total aflatoxins at a w 0.902 (260.4 μg/kg) was detected after 21 days, with an appreciable increment in the concentration of aflatoxins B 1 and G 1. These quantities were lower than those reported for aflatoxin production on other cereals and legumes, indicating that amaranth is not a good substrate for aflatoxin production. Zearalenone was not detected at a w 0.902. Maximum accumulation of zearalenone was 1.5 μg/g after 35 days at a w 0.925 and 11.1 μg/g after 49 days at a w 0.950.