Components of fiber bind iron in vitro.

Interactions among fiber, inorganic iron, and substances known to chelate iron were examined in vitro. Cellulose, neutral and acid fractions of lignin, psyllium mucilage, and pectin were incubated with 59Fe SO4 at various pH's, in various concentrations, and in the presence or absence of known chelators of iron including ascorbate, citrate, cysteine, fructose, and EDTA. Insoluble components of fiber were tested in a precipitation-centrifugation system, soluble components were tested by equilibrium dialysis. Lignins and psyllium mucilage had the greatest capacity to bind ferrous iron under conditions that approximated those of the proximal intestine postprandially; cellulose and pectin were less potent. Dissociation constants of binding were similar for several components, suggesting the existence of comparable binding sites in different components of fiber. Citrate and EDTA inhibited the binding of iron markedly but other chelators were much less effective. These reactions among fiber, inorganic iron, and other constituents of food may influence the bioavailability of dietary iron and the simple systems described here offer a means of dissecting interactions that are complex in vivo.