Flax seed has become an increasingly popular food ingredient because of its nutrient richness as well as potential health benefits. Flax seeds are often ground before consumption, and flax seed cakes are used as animal feed. Aflatoxin production may occur subsequently when the ground seeds are stored in an environment that supports fungal growth. The objectives of this study were to determine the growth of two toxigenic fungi, Aspergillus flavus and A. parasiticus, and to quantify the concentrations of four major aflatoxins (AFB1, AFG1, AGB2, and AFG2) produced by the two fungi on ground flax seeds with water activities (aws) of 0.82, 0.86, 0.90, 0.94, and 0.98, incubated for 30 days at 20, 27, and 35°C. Results of the study showed that A. flavus was able to grow on ground seeds with aw from 0.86 to 0.98 at all three temperatures, and the most rapid growth occurred at aws 0.90 and 0.94 at 27°C. In comparison, A. parasiticus grew on seeds with aw from 0.86 to 0.98 at 27 and 35°C as well as on seeds with aw from 0.86 to 0.90 at 20°C, and the most favorable growth condition was aw from 0.90 to 0.94 at 35°C. A. flavus produced aflatoxins on seeds with aw from 0.90 to 0.94 at 27°C as well as on seeds with aw from 0.86 to 0.98 at 35°C, and the maximum total aflatoxin (298 μg/kg), AFB1 (247 μg/kg), and AFG1 (51 μg/kg) were found on seeds with aw 0.90 at 35°C. In comparison, A. parasiticus produced aflatoxins under a wider range of conditions, which included aw 0.86 at 27 and 35°C, aw 0.90 at 20 and 27°C, aw 0.94 at 27°C, and aw 0.98 at 35°C. The maximum total aflatoxin (364 μg/kg) and maximum AFB1 (324 μg/kg) along with 34 μg/kg AFG1 and 6 μg/kg AFB2 were produced by A. parasiticus on seeds with aw 0.98 incubated at 35°C for 30 days. Linear regression models also indicated that high incubation temperature (35°C) was optimal for overall fungal growth and for formation of high levels of aflatoxin by both fungi. Future studies should also address aflatoxin contamination in flax seed oil.
Ground flax seed supported production of AFB1, AFB2, AFG1, and AFG2.
Neither A. flavus nor A. parasiticus grew on ground flax seeds with aw 0.82.
High levels of aflatoxin were produced by A. flavus under rapid growth conditions.
Under slow growth conditions, A. parasiticus produced high levels of aflatoxins.