Kinetic and mechanistic investigations on reductions of aflatoxins by lactic acid

The kinetics of reduction of AFB1 to AFB2 and AFG1 to AFG2 by lactic acid has been investigated in dilute aqueous acidic solutions (pH 3.35–4.50) as a function of the concentrations of lactic acid, AFB1, AFG1 and hydrogen ion at 37 °C. The rate of the reaction was found to be first order with respect to the concentrations of lactic acid and aflatoxins and independent on hydrogen ion concentration. The experimental results are interpreted in terms of mechanisms involving an initial formation of transient oxonium intermediate, which tends to polarize the olefinic (C=C) carbon, which in turn causes the hydride abstraction from α-carbon atom of lactic acid in rate determining step. The proposed mechanisms involve an overall transfer of two protons and two electrons from lactic acid to AFB1 and AFG1 to give the corresponding reduced less toxic products AFB2 and AFG2 and the oxidised product pyruvic acid.