Mineral binding capacity of insoluble fiber from extruded cereal brans.

Abstract

Insoluble fiber fractions from raw and extruded oat, rice, and wheat brans were isolated, and phytate removed. Soluble and insoluble fiber contents were determined, and mineral binding studies conducted, in vitro. The objectives of this study were: (1) to determine if extrusion screw-speeds (50, 70, and 100 rotations per minute) affect the brans' IF content, (2) to determine if extrusion screw-speeds (50, 70, and 100 rotations per minute) affect the IF mineral binding capacity, (3) to determine the total binding capacity of the brans' IF fraction, for Cu²⁺, Ca²⁺, and Zn²⁺, after the removal of phytate, (4) to determine if extrusion processing affects the phytate content of the samples. Raw brans served as controls. A twin-screw extruder, model DNDG-62/20 D was used, where die temperatures, and pressure were: 156 to 169°C/36 to 44 bars, for oat bran; 123 to 130°C/6 bars, for rice bran; and 112 to 122°C/2 bars, for wheat bran. It was found that, extrusion screw-speed did not affect the insoluble fiber content of wheat bran, however, a decrease was observed in rice, and oat bran. High screw-speeds led to an increase in the IF content, of oat and rice bran, whereas wheat bran was not affected. Soluble fiber content increased in all brans, which was attributed to a redistribution of the insoluble fiber. Even after phytate removal, the insoluble fiber, from all brans, bound Cu²⁺, Ca²⁺, and Zn²⁺. Oat bran bound more Cu²⁺ than wheat bran, which, bound more than rice bran. The brans bound equivalent amounts of Ca²⁺ and Zn²⁺. Overall, extrusion processing did not affect the brans' insoluble binding fiber capacity, for Cu²⁺, but it seems to have affected the insoluble fiber binding capacity, from rice and oat bran, for Ca²⁺ and Zn²⁺. Extrusion did not affect the brans' phytate content.