Fumonisin production in rice cultures of Fusarium verticillioides under different incubation conditions using an optimized analytical method

Fumonisin B 1 (FB 1) and fumonisin B 2 (FB 2) are the main members of a family of mycotoxins produced by various fungal species belonging to the Gibberella fujikuroi complex. The present work shows the results of a comparative study of various clean-up and derivatization procedures for analysis of fumonisins in rice cultures. Fumonisins were extracted from rice with acetonitrile/water (50/50, v/v). For clean-up, three solid-phase extraction procedures were assayed (C 18 cartridge, SAX cartridge, and a combination of both). Two reagents ( o-phthaldialdehyde and 4-fluoro-7-nitro-benzofurazan) were studied comparatively for formation of fluorescent derivatives. The separation was carried out by LC using a fluorescence detector. The best procedure for analysis of fumonisins in rice involved clean-up with C 18 cartridge and derivatization with o-phthaldialdehyde. The limit of detection was 0.010 mg kg −1 for both toxins. In the 10–500 mg kg −1 spiking level range, the recovery rates for FB 1 and FB 2 in rice varied from 94.6% to 103.6% and from 96.3% to 101.9%, respectively. The optimized analytical method for determination of fumonisins in rice was applied to the study of FB 1 and FB 2 production by four isolates of the G. fujikuroi species complex in rice cultures carried out at different temperatures and water activities to establish the influence of strain and environmental conditions on fumonisin production in this cereal. In general, fumonisin production was the highest at 20 °C and lowest at 37 °C. Four of the five assayed water activity ( a w) values (0.97, 0.98, 0.99, and 1.0) did not affect significantly fumonisin accumulation but fumonisins were not detected in cultures when a w was 0.96.