Antimutagenic activity of natural phenolic compounds present in the common bean (Phaseolus vulgaris) against aflatoxin B-1

Polyphenols with antimutagenic and anticarcinogenic properties are present in fruits, vegetables and legumes. In this study, the Salmonella typhimurium tester strains TA98 and TA100 were used in the microsuspension assay to examine the antimutagenic effect of phenolic compounds extracted from the common bean (Phaseolus vulgaris) against mutagenicity induced by aflatoxin B-1 (AFB(1)). A dose-response curve was constructed for AFB(1); from which a level of 40 ng AFB(1)/tube was selected for all antimutagenicity assays. The AFB(1) and phenolic extract (PE) were not toxic to the bacteria at concentrations tested. In the case of PE, results were similar to the number of spontaneous revertants for TA98 and TA100. The inhibitory effect of PE against AFB(1) mutagenicity was dose-dependent at the lower concentrations tested (2.5, 5, 10, 12.5, 15 and 25 mug-equivalent (+)-catechin/tube for TA98; 0.5, 1, 1.5, 2.5, 5, 10 and 25 mug-equivalent (+)-catechin/tube for TA100). Further, a two-stage incubation procedure was used to investigate the potential interaction between PE and AFB(1). The greatest inhibitory effect of the PE on AFB(1) mutagenicity occurred when PE and AFB(1) were incubated together. When the bacteria were first incubated with PE followed by a second incubation with AFB(1), lower inhibition was observed. Lower inhibition was also observed when the bacteria were first incubated with AFB(1) followed by a second incubation with PE. The results suggest that the mechanism of inhibition could involve the formation of a chemical complex between of PE and AFB(1).