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

Water-soluble dietary fiber (WSDF), water-insoluble dietary fiber (WIDF) fr om wheat bran, and the carboxymethylated product of WIDF (CIDF), all having low contents of protein, ash, and phytic acid, were evaluated for their sc avenging capacity far three heavy metals, Hg, Cd, and Pb. The results showe d that WIDF had higher BCmax (maximum amount of bound heavy metal ions) and BCmin, values (minimum concentration of heavy metal ions below which the i ons 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 h eavy metals (increase in BCmax and decrease in BCmin). The pH value signifi cantly affected the binding capacity for heavy metals; BC,, sharply increas ed and BCmin sharply decreased for each heavy metal ion for all of the diet ary fibers when the pH was raised fi om 2.0 to 7.0. The binding capacity of dietary fibers for heavy metals was slightly affected by amino acids, calc ium, iron, and zinc but significantly affected by copper. Colon fermentatio n released part of the heavy metal ions from dietary fibers. From the resul ts 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 b y their toxicity.