ANTI-AFLATOXIN MUTAGENIC FACTORS IN CORN

Extracts, isolated through sequential fractionation and partition proc edures described previously (Martinet et al. 1994) from aflatoxin-free corn and aflatoxin-contaminated corn with and without ammonia treatme nt, were investigated for mutagenic potential using the Ames test (TA 100 tester strain). 2-Aminofluorene (2-AF) and pure aflatoxin B-1 (AFB (1)) were used as positive controls. Although TA100 showed mutagenic r esponse to pure AFB(1) at a dose of ca 10 ng/plate, all isolates teste d from ammonia-treated aflatoxin-contaminated corn containing 7500 ng AFB(1)/g did not exhibit positive results in the Ames test. Additional ly, isolates from non-ammonia-treated aflatoxin-contaminated corn fail ed to give positive mutagenic potentials. These results indicate that differences between the mutagenic potentials of pure aflatoxins and of aflatoxins in naturally-contaminated corn exist. CH2Cl2 extracts (the fractions containing aflatoxins) obtained from aflatoxin-contaminated corn with and without ammonia treatment were applied to preparative t hin layer chromatography (TLC) in an effort to separate aflatoxins and /or ammonia/aflatoxin reaction products from the 'unknown interfering materials' existing in the corn matrix. Each of the fractions separate d by TLC was tested by the Ames test with S9 activation and none of th em gave a mutagenic response to TA100. CH2Cl2 extracts in dimethylsulp hoxide (DMSO) obtained from non-ammonia-treated aflatoxin-free corn we re spiked with pure AFB(1) and tested by TA100 with S9 activation. Aga in, no positive responses were observed. These findings provide furthe r evidence of 'unknown interfering materials' in corn which may bind w ith aflatoxin and/or can be extracted by CH2Cl2 together with aflatoxi n, and, therefore, block the mutagenic activity of aflatoxin in the Am es test. Those materials were not separated from the aflatoxins by the TLC technique used in the present study. Possible reasons and further studies required to evaluate this phenomenon are discussed.