In vitro mineral binding capacity of five fiber sources and their insoluble components for copper and zinc

Five fiber-rich food sources, wheat bran (WB), rice bran (RB), oat fiber (OF), apple fiber (AF), and tomato fiber (TF) and their isolated insoluble fiber fractions were evaluated in vitro for their binding capacity for zinc (Zn) and copper (Cu). Endogenous Zn concentrations of the fibers varied from 11.0 mu g/g for OF to 136.0 mu g/g for WB, whereas Cu concentrations ranged from 1.0 mu g/g for OF to 14.0 mu g/g for WB. In all the fibers, total Cu bound was significantly higher than Zn. Total Cu bound ranged from 3687 mu g/g for OF to 8019 mu g/g and 8073 mu g/g for WB and AF, whereas, bound Zn levels varied from 1213 mu g/g for OF to 7121 mu g/g and 7166 mu g/g for WB and RB, respectively. Significantly more Zn and Cu were bound by the fiber fractions than the whole fibers, probably due to the exposure of more binding sites on the polymers during the fractionation process. Generally, the fiber components of all five fibers showed Cu and Zn binding capacities decreasing in the order; hemicellulose A > lignocellulose > lignin > cellulose. A strong correlation was seen between the combined effects of protein, hemicellulose, and lignin contents of the fibers versus total Zn binding capacity and a lesser correlation with Cu.