Destruction of Aflatoxin B₁ with Sodium Bisulfite: Isolation of the Major Product Aflatoxin B₁S

The reaction between aflatoxin B₁ and sodium bisulfite yielded almost quantitatively a light yellow, highly fluorescent water-soluble product, aflatoxin B₁S. Reverse-phase (C₁₈) high pressure liquid chromatography (with and without the paired-ion technique), and normal- and reverse-phase thin layer chromatography revealed the ionic product at greater than 98% yield. The product's intense fluorescence, identical in color to that of aflatoxins B₁ and B₂, supported the conclusion that the lactone of aflatoxin B₁ was not opened by bisulfite and that the reaction took place at some other location on the aflatoxin B₁ molecule. The UV spectrum of aflatoxin B₁S exhibited identical absorbance maxima to aflatoxin B₁ and these maxima exhibited no bathochromic shift in alkaline solution. Aflatoxin B₁S exhibited change to bright yellow fluorescence under 365 nm UV light after being sprayed with 20% sulfuric acid in methanol. The IR spectrum of aflatoxin B₁S indicated the vinylene group of the furofuran ring system of aflatoxin B₁ was missing from aflatoxin B₁S, whereas the coumarin-cyclopentenone ring system present in aflatoxin B₁ was intact in aflatoxin B₁S. Furthermore, the IR spectrum suggested the presence of a sulfonate moiety in B₁S. Proton NMR spectra of aflatoxin B₁S also indicated that the cyclopentenone region was intact and that the furofuran had undergone reaction with bisulfite. Integration of the NMR spectrum of aflatoxin B₁S revealed 12.75 to 13.25 protons, consistent with a bisulfite addition across the double bond of aflatoxin B₁ to form aflatoxin B₁S. Aflatoxins B₂ and G₂ were not susceptible to the action of bisulfite, again supporting the conclusion that bisulfite acts at the unsaturation in the furofuran ring system of aflatoxin B₁. There was no evidence that aflatoxin B₂ was produced in the degradation of aflatoxin B₁ by bisulfite under these conditions. The fact that previously reported chemical modifications of this furofuran ring system resulted in reduced toxicity support the potential utility of bisulfite as a means of detoxification of aflatoxin-contaminated commodities.