The effect of dry heat on the bioavailability of iron in soy flour

Bioavailability of iron in soy flour was investigated by the Hemoglobin Regeneration Efficiency (HRE) procedure in 50 three‐month‐old Sprague‐Dawley rats. Rats weighing 250 ±7 g and with a mean hemoglobin level of 12.9 g/dl were randomly assigned to one of five treatment groups: baseline (BL), unheated soy flour (UH), soy flour heated at 225°F for either 10 min (H10), 30 min (H30), or 120 min (H120). The animals were fed diets (46 ppm iron) containing the soy flour for 21 days. HREs of UH, H10, H30, H120 diets were 17.6, 16.8, 17.7 and 16.8%, respectively. Apparent iron absorption from the UH, H10, H30 and H120 diets was 94.7, 94.3, 93.9 and 94.3%, respectively. Serum iron was significantly lower (p<.001) and total iron binding capacity was significantly higher (p<.001) in rats fed the H120 diet. Iron concentrations in the liver, spleen, heart and kidney were significantly lower in rats fed H30 or H120 diets. These results suggest that prolonged heating of soy flour may reduce iron bioavailability and result in depletion of iron stores.