Destruction of aflatoxin B1 with sodium bisulfite: Isolation of the major product aflatoxin B1S

Abstract

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 furoran ring system resulted in reduced toxicity supports the potential utility of bisulfite as a means of detoxification of aflatoxin-contaminated commodities.