Heat treatment on heme iron and iron-containing proteins in meat: Iron absorption in humans from diets containing cooked meat fractions

The present study was undertaken to characterize the effect of heat on iron compounds and iron-containing proteins of rabbit meat. We also studied human iron absorption from beef meat precipitates and investigated changes in the cysteine content in beef and rabbit meat caused by cooking processes. Supernatant and precipitate fractions were obtained by an extraction procedure that included homogenization and repeated centrifugations. A 50% decrease of soluble iron was produced by cooking the meat. Cooking also reduced the heme iron content of the meat by 62%. Chromatographic separation of soluble meat extracts showed changes in ferritin, hemoglobin, and myoglobin elution profiles in cooked meat compared with raw meat. Determinations of the cysteine content in raw or cooked meat samples showed a statistically significant reduction (P < 0.0001) in the cysteine content in cooked samples compared with raw counterparts. Iron absorption studies in humans Seeding the subjects with a typical beef-containing diet, which contained 60% of meat iron as heme iron, showed a 13.5% absorption from heme iron and a 6.3% from nonheme iron. The subjects fed with a diet containing beef precipitate in which only 30% of meat iron was heme iron showed a 7.6% absorption from heme iron and 7.5% from nonheme iron. These results show that although there are important changes in iron-containing proteins, heme iron, cysteine content, and iron absorption by cooking procedures, the factor present in meat responsible for enhancing nonheme iron absorption is not affected by heat and is still present in insoluble meat precipitates.