Biological availability to the rat of intrinsic and extrinsic iron with soybean protein isolates.

Evaluations were conducted to assess the biological availability of iron in three food grade isolated soybean proteins and to evanuate the influence of these proteins on iron added to the diet from a source of known high biological availability. Ferrous sulfate was used as the standard iron source in all experiments. The biological availability was measured by a 14-day hemoglobin repletion after a 4 week depletion period using multiple dose response and comparing the test samples and standard iron source by the slope ratio assay procedure. The relative iron bioavailability for three isolated soybean proteins was A = 60%; B = 64% and C = 59% with a mean value of 61%. Autoclaving isolated soybean protein B at 108.4 degrees improved iron bioavailability over the unheated samples while isolated soybean protein A was unaffected by this treatment. Iron added to the diets containing isolated soybean protein had bioavailabilities similar to that of iron present in the soybean which supports the common dietary iron pool hypothesis. The high iron content (0.18 mg/g protein) coupled with the bioavailability data make the isolated soybean proteins a good dietary iron source.