59D-2 |
Chelation and reduction of nonheme iron by sulfhydryl groups in chicken muscle protein digests |
D. A. VATTEM, Food Science, University of Massachusetts, Amherst, MA 01003 and R. R. Mahoney. It is well established that muscle proteins enhance the uptake of nonheme iron-an effect known as the “meat factor”.The mechanism is not yet clear but several studies indicate that peptides resulting from digestion chelate and reduce the iron so as to enhance its solubility in the intestinal tract. This interaction of peptides with iron must depend upon specific amino acid residues which have not been clearly identified. Since muscle proteins are rich in sulfhydryl residues, our objective was to investigate their role in chelation and reduction of ferric iron. Chicken breast muscle was extracted with dilute salt solution to separate the soluble and insoluble protein fractions. After heating the fractions were digested with pepsin and pancreatin. Iron chelation was measured by adding ferric iron at pH 2 to the digests, raising the pH to 6 and determining soluble iron.Sulfhydryls in the digests were modified with N-ethlymaleimide(NEM), p-chloromercuribenzoate(pCMB) and by oxidation with oxygen gas(OX). Binding and reduction of iron led to a decrease in free sulfhydryl groups of 75% and 72 % for the soluble and insoluble fractions, respectively. Modification of the sulfhydryls led to a loss of about 90% of the original content in both fractions, for all three methods. For the soluble fraction this was accompanied by a reduction in iron binding of 78%for NEM, 77% for pCMB and 83% for OX.For the insoluble fraction the reduction in iron binding was 70% for NEM, 59% for pCMB and 69% for OX.The change in ferrous iron was proportional to the change in total iron bound. The results show that sulfhydryl groups are involved in chelation and reduction of iron and are modified as a consequence.Quantitatively, the results indicate that in chicken muscle proteins sulfhydryls are the single most important residue involved in iron chelation but that other residues may play a small role.
Session 59D, Food Chemistry: Proteins and Physicochemical Properties
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