ABSTRACTWhite potatoes did not support the growth ofA. parasiticusNRRL 2999 unless they were heated to above 60° C. The mold grew well on autoclaved potatoes and produced, on an average, 8 μg/g total aflatoxins (mainly B1and G1) at 27°C and 95–97 relative humidity in 20 days. When soluble potato starch was substituted for sucrose in yeast extract‐sucrose (YES) medium, the maximum growth ofA. purasiticuswas 80 of that observed in YES medium, but total aflatoxin production was only 0.5–1.0 of the production in YES medium. Chlorogenic acid and solanine, at levels normally found in the white potato, did not show appreciable fungitoxic activity towardsA. parasiticusin vitro. Caffeic acid partially inhibited the growth ofA. parasiticusand the production of aflatoxins at 0.01M concentration in YES medium. A compound with high inhibitory activity towardsA. parasiticuswas isolated from the potatoes. The compound is extractable with ethyl acetate. From its behavior on TLC systems, its ultraviolet spectrum and its reactions with chromagenic spray reagents, it is inferred that the compound is phenolic in nature. It appears to be a hydroxy‐cinnamic acid derivative structurally similar to caffeic acid but lacking the ortho‐dihydroxy structure of
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