chapter  16
18 Pages

Bioassay-Directed Isolation and Identifi cation of Antiafl atoxigenic Constituents of Walnuts

WithRussell J. Molyneux, Noreen Mahoney, Jong H. Kim, Bruce C. Campbell

Aatoxins are polyketide metabolites most commonly produced by certain strains of the fungi Aspergillus flavus and A. parasiticus, which can infect a number of major agricultural crops, including corn, peanuts, cotton, and tree nuts. The most common of these metabolites are aatoxins B1 (1) and B2 (2), and G1 (3) and G2 (4), with aatoxins B2 and G2 being the 8,9-dihydro derivatives of (1) and (3), respectively (Figure 16.1). The B and G groups differ in the presence of cyclopentanone and δ-lactone moieties, respectively. In general, A. flavus produces the B group aatoxins

whereas A. parasiticus produces both B and G groups. Although not all strains of A. flavus and A. parasiticus are capable of producing aatoxins (i.e., are “aatoxigenic”) the contamination of human and animal food crops by these compounds is of great concern because they are classied as carcinogens, particularly in humans infected with hepatitis.1,2 On occasion these compounds can be acutely toxic, as illustrated by a recent episode in rural Kenya where contaminated maize led to 317 cases of poisoning and 125 deaths.3