INHIBITORY EFFECT OF A SOYBEAN-PROTEIN RELATED MOIETY ON IRON-ABSORPTION IN HUMANS

The inhibitory effect of soybean protein isolates on nonheme-iron abso rption was studied in 34 human subjects. Iron absorption was measured by using an extrinsic radioiron label in liquid-formula meals containi ng hydrolyzed corn starch, corn oil, and either egg white or a series of soybean-protein derivatives. The unmodified soybean-protein isolate markedly inhibited iron absorption. Percentage absorption was 19-fold higher when an extensively enzyme-hydrolyzed preparation with very li ttle phytate was used as the protein source. Both the glycinin (11S) a nd conglycinin (7S) fractions of soybean protein were inhibitory to ir on absorption. Dephytinization removed the inhibitory effect of the gl ycinin but not of the conglycinin fraction. We conclude that there are two major inhibitors of iron absorption in soybean-protein isolates, phytic acid and a protein-related moiety contained in the conglycinin (7S) fraction.