Comparison of the effect of cell wall and hull fiber from canola and soybean on the bioavailability for rats of minerals, protein and lipid.

Hull or cell wall material, isolated from canola (Brassica napus cv. Regent) or soybean (Glycine max) or cellulose was added to a basal, semipurified diet at a level of 12% and fed to growing male Wistar rats. The apparent availability of Cu, Fe, Ca, P and protein were lower when the fiber-containing diets were fed compared to the control diet. The availability of Mg was lower when the canola hull (CH) and cellulose (CE) diets were fed, whereas Zn availability was lower when the canola cell wall (CCW) and CE diets were fed, compared to the control diet. Determination of the feed transit time, by using the unabsorbable marker Cr2O3, demonstrated that the CE and soybean cell wall (SCW) diets had the fastest transit rates, followed by the CH, soybean hull (SH), CCW and control diets. Determination of the in vitro binding of the various fibers to metal ions demonstrated that CH was the strongest chelator, whereas CE had the lowest binding affinity for any of the minerals tested. At the termination of the trial, intestinal segments were removed and the in vitro mucosal transport of Cu, Fe, Mn and Zn were compared. The CCW diet consistently demonstrated lower transport for the four minerals, especially in the ileal segment.