Anti-aflatoxin mutagenic factors in corn.

ABSTRACT

Extracts, isolated through sequential fractionation and partition procedures described previously (Martinez et al. 1994) from aflatoxin-free corn and aflatoxin-contaminated corn with and without ammonia treatment, were investigated for mutagenic potential using the Ames test (TA 100 tester strain). 2-Aminofluorene (2-AF) and pure aflatoxin B1 (AFB1) were used as positive controls. Although TA100 showed mutagenic response to pure AFB1 at a dose of ca 10 ng/plate, all isolates tested from ammonia-treated aflatoxin-contaminated corn containing 7500 ng AFB1/g did not exhibit positive results in the Ames test. Additionally, isolates from non-ammonia-treated aflatoxin-contaminated corn failed 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 thin 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 separated by TLC was tested by the Ames test with S9 activation and none of them gave a mutagenic response to TA100. CH2Cl2 extracts in dimethylsulphoxide (DMSO) obtained from non-ammonia-treated aflatoxin-free corn were spiked with pure AFB1 and tested by TA100 with S9 activation. Again, no positive responses were observed. These findings provide further evidence of "unknown interfering materials' in corn which may bind with aflatoxin and/or can be extracted by CH2Cl2 together with aflatoxin, and, therefore, block the mutagenic activity of aflatoxin in the Ames 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.