Protein-binding of Ochratoxin A and Its Extractability from Proteinous Food

Abstract

The binding potential of ochratoxin A (Oct. A), a carcinogenic mycotoxin, to protein was investigated by using bovine serum albumin (BSA) and proteinous food. An interaction between Oct. A and BSA was suggested in the aqueous system, where fluorescence with high intensity was observed. This was also confirmed by thin-layer chromatography on a microporous cellulose acetate membrane. Measurements of the extractability of Oct. A with chloroform showed that the binding ability was high in the range of pH 4.0 to 6.0. The major binding type was presumed to be ionic, based on a comparison with the extractability of ochratoxin A methyl ester. The binding parameters determined by an equilibrium dialysis method were n=2.38±0.17 for the number of binding sites and K=7.67±0.39 (×105/M) for the affinity constant in phosphate buffer at pH 7.4. The binding was weakened with increasing ionic strength of the solution and with increasing content of methanol. On the basic of these results, the first extraction procedure for Oct. A by the A. O. A. C. method, which gave a low extractability of 29% for Katsuobushi, dried bonito meat rich in protein, was modified to obtain a high recovery. The addition of 2M sodium chloride and further acidification by addition of 4 volumes of 0.5M phosphoric acid resulted in an increase of the extractability to 85%.