BINDING OF ZINC TO APPLE FIBER, WHEAT BRAN, AND FIBER COMPONENTS

Zinc ion binding to commercial brans, fiber, and fiber components was studied by equilibrium dialysis. Maximum initial concentration of zinc bound by 50 mg of apple fiber (AF) and wheat bran (WB) at pH 7.2 was 220 mug. AF and WB binding capacities were significantly lower for soluble fractions than for unfractionated materials. The water-soluble fraction's binding capacity was 90% lower for AF than for WB. Hemicellulase and phytase slightly increased AF binding capacity but reduced WB capacity. Pectinase increased both AF and WB capacity slightly. Binding capacities of commercially available individual fiber components decreased in the order: lignin > polypectin > pectin > gum > cellulose. Zinc-binding capacities of various dietary fiber types differ, accounting for different zinc bioavailabilties of some foods.