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Abstract
Fumonisin B$\sb1$ (FB$\sb1$) contaminates corn-based foods worldwide, suggesting that this mycotoxin survives many food processing procedures. Aqueous solutions of FB$\sb1$ at pH 4, 7 and 10 were heated to 100-235$\sp\circ$C and processed for 60 min. High performance liquid chromatography indicated that FB$\sb1$ was relatively heat stable and decomposed into at least three major hydrolysis products. The rate and extent of FB$\sb1$ decomposition was dependent upon the pH and increased with increasing processing temperature. Overall, FB$\sb1$ was least stable at pH 4, followed by pH 10 and 7, respectively.
Components of a food matrix may interact with FB$\sb1$ during processing. Thermal processing of aqueous FB$\sb1$ solutions containing glucose at 100-125$\sp\circ$C resulted in an apparent decrease in FB$\sb1$ content related to a nonoxidative, Maillard-type browning reaction, rather than actual decomposition. Bioassays using brine shrimp indicated that the toxicity of FB$\sb1$ solutions was reduced following processing with glucose.
Twenty-five domestic U.S. and four imported commercial beer brands were analyzed for contamination with FB$\sb1$ and FB$\sb2$. Of a total of fifty-eight beers sampled, 72% were positive for FB$\sb1$ and 29% were positive for FB$\sb2$, with a limit of quantitation for each toxin of 0.3 ng/ml. The total fumonisin content of positive samples ranged from 0.3 to 12.7 ng/ml and may represent typical background levels in beer.
To attest that toxicity is lost upon modification of FB$\sb1$, biological activity must be evaluated. Chicken embryos, brine shrimp (Artemia salina) and Madin-Darby canine kidney (MDCK) cells were utilized in short term toxicity bioassays to assess their sensitivity to FB$\sb1$. An MTT assay indicated that FB$\sb1$ was not highly cytotoxic to MDCK cells with a calculated IC50 of 253 $\pm$ 7 $\mu$M FB$\sb1$. The injection of aqueous FB$\sb1$ solutions into the air space of fertile chicken eggs, resulted in an LD50 of 52 $\mu$g FB$\sb1$/egg, or 1.3 $\mu$M FB$\sb1$. An optimized brine shrimp bioassay using 96-well plates and a 48 h mortality endpoint resulted in an LC50 of 1.7 $\mu$M FB$\sb1$, or 1.2 $\mu$g FB$\sb1$/ml. The brine shrimp bioassay has potential for screening for FB$\sb1$ contamination in food samples.
