Solubilization of iron by digests of chicken muscle protein
The solubilization of ferric iron by in vitro digests of chicken muscle proteins was studied. Non-muscle proteins (ovalbumin and casein) were similarly evaluated. The dilute salt insoluble proteins (DSIP) solubilized twice as much iron as the dilute salt soluble proteins. Most of the iron solubilized was ferrous. Only 1% of the total iron solubilized was dialyzable. Maximum iron solubilization was obtained after digestion with pepsin (3 hours) and pancreatin (0.5 hour). Ovalbumin and casein solubilized significantly (p $<$ 0.05) more iron than the DSIP. These proteins may not however enhance iron uptake in vivo.
Ultrafiltration of iron-protein digests indicated that most of the iron was bound to proteins or peptides whose molecular weight (MW) was greater than 10000. However, when large (MW $>$ 10000) and small (MW $<$ 10000) peptides were separated by ultrafiltration, their total iron solubilizing capacity was similar. Ultrafiltration could be used to isolate the iron binding peptides of the DSIP fraction.
Iron solubilization by DSIP was accompanied by loss of some histidyl and sulfhydryl residues. Chemical modification of each of these residues led to a decrease of about 30% in iron solubilization. Similar effects were observed with free histidine and cysteine but not with glutathione. Interaction of iron with these residues could not account for all the iron solubilized by the DSIP. It was therefore likely that residues or interactions other than these were involved in iron solubilization by the DSIP peptides.
It was concluded that the DSIP digest solubilizes iron and enhances iron bioavailability by both complexation and reduction of dietary ferric iron to the more soluble ferrous form partly through its histidyl and sulfhydryl residues.
0486: Analytical chemistry