An in vitro study of wheat bran binding capacity for Hg, Cd, and Pb

Water-soluble dietary fiber (WSDF), water-insoluble dietary fiber (WIDF) from wheat bran, and the carboxymethylated product of WIDF (CIDF), all having low contents of protein, ash, and phytic acid, were evaluated for their scavenging capacity for three heavy metals, Hg, Cd, and Pb. The results showed that WIDF had higher BC(max) (maximum amount of bound heavy metal ions) and BC(min) values (minimum concentration of heavy metal ions below which the ions cannot be bound by dietary fibers) than WSDF at two pH conditions (pH 2.0 and 7.0). Carboxymethylation of WIDF improved its binding capacity for heavy metals (increase in BC(max) and decrease in BC(min)). The pH value significantly affected the binding capacity for heavy metals; BC(max) sharply increased and BC(min) sharply decreased for each heavy metal ion for all of the dietary fibers when the pH was raised from 2.0 to 7.0. The binding capacity of dietary fibers for heavy metals was slightly affected by amino acids, calcium, iron, and zinc but significantly affected by copper. Colon fermentation released part of the heavy metal ions from dietary fibers. From the results it can be concluded that dietary fibers from wheat bran can effectively bind all three tested metal ions to prevent the body from being affected by their toxicity.