Penitrem and thomitrem formation by Penicillium crustosum.

The levels of penitrems A, B, C, D, E, F, roquefortine C and thomitrem A and E recovered from extracts of 36 Norwegian, 2 American and one each of Japanese, German, South African, Danish and Fijian isolates of Penicillum crustosum Thom were quantitatively determined using high performance liquid chromatography-mass spectrometry (HPLC-MS). Forty-two of the 44 isolates of penitrem-producing isolates grown on rice, afforded levels of thomitrem A and E comparable to that of penitrem A. Thomitrems A and E were also found, but at lower levels, when cultures were grown on barley. No thomitrems were found when the isolates were grown on liquid media. The effects of time and temperature on mycotoxin formation were studied on rice over a 4 week period at 10, 15 and 25 degrees C, respectively. No mycotoxins could be detected after 1 week at 10 degrees C, but after 2 weeks at 10 degrees C levels were similar to those produced at 15 and 25 degrees C. Higher levels of thomitrems A and E were detected when media were maintained at lower pH. The possibility that thomitrems A and E might be derived by acid promoted conversion of penitrems A and E was explored in stability trials performed at pH 2, 3, 4, 5 and 7 in the presence and absence of media. Thomitrems were formed at pH 2, 3 and 4 but not at pH 5 and 7.