Isolated Fiber Components and pH Alter Methylazoxymethanol Acetate Mutagenicity

Dietary fibers, 300 ug of pectin, lignin, hemicellulose, or cellulose, were preincubated with either 1500 uM, 1000 uM, 750 uM, or 500 uM of the mutagen methylzoxymethanol acetate (MAM acetate) at pH 5.4,2.1, and 6.6 simulating gastrointestinal conditions. A modification of the Ames assay was used with Salmonella typhimurium his G46 and no S-9 activation to determine any change in mutagenic activity of MAM acetate with and without the individual fiber components at each pH level. AtpH 5.4 MAM acetate was only weakly mutagenic, therefore it was difficult to assess the effect of the fiber components. MAM acetate displayed the highest level of mutagenicity at pH 2.1. At pH 2.1 the percent inhibition of MAM acetate induced revertants with pectin and hemicellulose was greater than 99%. Lignin caused 91% inhibition, but cellulose did not effectively inhibit mutagenicity. At pH 6.6 MAM acetate was mutagenic only with 1500 uM and 1000 uM concentrations. At pH 6.6 lignin and hemicellulose caused 99% inhibition, pectin 97%, and cellulose 38%. The results indicate that the effect of dietary fiber on mutagenicity is dependent on the specific fiber component tested, and support the theory that inhibition of mutagenicity is due to binding of the mutagen with the fiber component.