Mineral binding capacity of dephytinized insoluble fiber from extruded wheat, oat and rice brans

Insoluble fiber fractions from raw and extruded oat, rice and wheat brans were isolated and phytate removed. In vitro mineral binding studies were performed utilizing copper (Cu2+), calcium (Ca2+) and zinc (Zn2+) ions, which were added individually to enzymatically treated (Prosky et al., 1985), acid washed insoluble fiber residues from oat, rice and wheat brans. The enzymatic digestion step with alpha-amylase, protease and amyloglucosidase served to remove protein and starch from the samples. Mineral binding studies were performed on the insoluble fiber residue. Mineral content was determined by flame atomic absorption spectroscopy. Raw brans served as controls. A twin-screw extruder Model DNDG-62/20D, manufactured by Bühlerag (CH-9240, Uzwil, Switzerland) was utilized. The objectives of the study were to determine the total Cu2+, Ca2+ and Zn2+ binding capacity of the dephytinized insoluble fiber from each bran; and to determine if extrusion screw speed affected the brans' insoluble fiber mineral binding capacity. Although dephytinized, the brans' insoluble fiber fraction bound Cu2+, Ca2+ and Zn2+ ions. Oat bran bound more Cu2+, Ca2+ and Zn2+ than wheat bran, which bound more than rice bran. Extrusion processing did not affect the brans' insoluble fiber binding capacity to bind Cu2+. However, it increased the binding capacity of Ca2+ and Zn2+ of the insoluble fiber fraction from rice and oat brans.