THE INTESTINAL TRUE ABSORPTION OF ZN-65 IN RATS IS ADVERSELY AFFECTEDBY DIETS CONTAINING A FABA BEAN (VICIA-FABA L) NONSTARCH POLYSACCHARIDE FRACTION

The effects on the absorption of Zn-65 by two varieties of raw faba be an (Vicia faba L., minor) or seed components that may interfere with m ineral metabolism in the gut, have been studied in growing rats. In be an diets all protein was supplied by the meals, and the fractions were tested by incorporating them in control diet at the same levels as th ey occur in the seeds. Absorption of Zn-65 was also measured in rats f ed dephytinized bean meal produced by including phytase in the diet. R ats were pair-fed diets supplemented with amino acids and minerals to target requirements and containing 40 mg Zn/kg diet, True absorption o f Zn was 50-70% lower in rats fed diets containing both cultivars of f aba bean meals than in those fed the control diet. Although soluble no nstarch polysaccharides caused a significant reduction in the absorpti on of Zn, this effect disappeared after the removal of phytate by demi neralization. In contrast, despite its negligible content of phytate, the insoluble nonstarch polysaccharides in the cell wall fraction of t he cotyledon accounted for most of the reduction in Zn absorption in r ats fed the faba bean diets. Addition of phytic acid to the control di et significantly reduced the absorption of Zn-65 but only from 44 to 3 6%. Moreover, the increase in the absorption of Zn was similarly small , from 21% to 29%, with the addition of phytase to the faba bean diet. These results suggest that, in addition to phytic acid, the insoluble nonstarch polysaccharides present in the cell walls of the cotyledon in Vicia faba seeds are mainly responsible for the lower Zn availabili ty in rats fed faba bean diets.