Growth and Aflatoxin B1, B2, G1, and G2Production by Aspergillus flavusand Aspergillus parasiticuson Ground Flax Seeds (Linum usitatissimum)

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 flavusand 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. flavuswas able to grow on ground seeds with awfrom 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. parasiticusgrew on seeds with awfrom 0.86 to 0.98 at 27 and 35°C as well as on seeds with awfrom 0.86 to 0.90 at 20°C, and the most favorable growth condition was awfrom 0.90 to 0.94 at 35°C. A. flavusproduced aflatoxins on seeds with awfrom 0.90 to 0.94 at 27°C as well as on seeds with awfrom 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 aw0.90 at 35°C. In comparison, A. parasiticusproduced aflatoxins under a wider range of conditions, which included aw0.86 at 27 and 35°C, aw0.90 at 20 and 27°C, aw0.94 at 27°C, and aw0.98 at 35°C. The maximum total aflatoxin (364 μg/kg) and maximum AFB1(324 μg/kg) along with 34 μg/kg AFG1and 6 μg/kg AFB2were produced by A. parasiticuson seeds with aw0.98 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.