Effects of heat treatments and freezing on content of different forms of iron in meats

Abstract

Dietary iron is existed in two forms, heme and nonheme iron. Absorption of heme is higher than that of nonheme iron. Solubility of iron is another factor that affects iron absorption because the iron that can be absorbed must be in a soluble form. Consequently, the alterations of heme and soluble iron contents may affect iron bioavailability. Meat, liver and heart of cow, pig and chicken are analyzed for iron contents by UV-Visible spectrophotometry and atomic absorption spectrophotometry. Average heme iron contents of meat, liver and heart are 10.83, 33.01 and 22.62 ug/g wet weight, respectively and soluble iron contents of meat, liver and heart are 2.45, 9.34 and 3.21 ug/g wet weight, respectively. Effects of boiling, drying and freezing on iron forms of meat are also studies. Boiling meat for 15, 30 and 60 minutes causes 12%, 19% and 25% reductions of heme iron content, respectively; on the other hand, increasing of soluble iron content, namely 34%, 54%, 81% is detected, respectively. A 32% decrease of heme iron content and an 186% increase of soluble iron content are obtained after sample is dried at 50-60℃ for 8 hours. Freezing at -20℃ for 4 weeks does not affect heme iron content of meat significantly. Soluble iron contents of different kinds of meat are differently affected. In general, the soluble iron content is insignificantly changed by freezing for four weeks, but it is found that the soluble iron contents of beef round, pork liver, pork heart and chicken liver are increased. Changes of heme and soluble iron contents from various heat treatments or freezing may probable alter bioavailability of meat iron. Therefore, in order to conserve nutritive value of meat, prolong cooking should be avoided for the sake of minimizing heme destruction. Freezing is suggested as a better method than drying for preservation of meat.