Effect of Iron Sources and Ascorbic Acid on the Chemical Profile of Iron in a Soy Protein Isolate

Abstract

The chemical changes in the iron profile of a commercial soy protein isolate resulting from ascorbic acid and iron fortification were examined. An in vitro method was devised to simulate gastrointestinal pH and an "enhancing factor" developed as a potential in vitro indicator of iron bioavailability. Ascorbic acid supplementation of soy protein produced substantial increases in soluble iron at pH 4 and 6. The solubilizing effect of ascorbic acid on iron was concentration and pH-dependent and contingent upon the exogenous iron source present. The exogenous iron entered a different chemical pool than the endogenous iron, thus raising questions about the concept of a nonheme pool at high levels of exogenous iron.

Characterization of Solution Properties of Four Iron Sources in Model Systems by Solubility Studies and IR/VIS Reflectance Spectrophotometry

“…This resulted in a protective effect on the iron in the AA treated model systems from most time-dependent fluctuations in iron insolubilization due to hydrolysis. This solubilizing effect of ascorbic acid has been previously noted by Clydesdale (1979, 1980) and Clydesdale (1982Clydesdale ( , 1983.…”

“…This occurred despite the face that these solutions ranged in pH from 4.5 to 7.5. Ascorbic acid may solubilize ferric iron both by complexation an&or by reduction to Fe2+ (Clydesdale, 1982(Clydesdale, , 1983. The reduction of Fe3+ to Fe2+ is well-known chemically and has previously been identified in food by Hodson (1970) and Rizk and Clydesdale (1984).…”

“…Some chelating agents may bind iron and prevent hydrolysis or minimize its effects (Chaberek and Martell, 1959). Much attention has been given to ascorbic acid (AA) due to the remarkable increase in iron absorption noted when it is consumed with iron-containing meals (Forth and Rummel, 1975;Hallberg, 1981;Clydesdale, 1982Clydesdale, , 1983.…”

Effect of Acid Pretreatment on the Stability of Citric and Malic Acid Complexes With Various Iron Sources in a Wheat Flake Cereal

“…Analyses. All samples were analyzed in duplicate for total iron, elemental iron, total nonelemental, total soluble, insoluble nonelemental, soluble complexed, total ionic, ferrous and ferric iron by a procedure adapted from Lee and Clydesdale (1979) as described by Rizk and Clydesdale (1983). It should be noted that while the term "ionic iron" is used throughout the paper, "bathophenanthroline reactive iron " is implied, since some complexed iron may be preferentially bound by the bathophenanthroline prior to extraction by CHC13, as discussed by Clydesdale and Nadeau (1984).…”

Effect of Acid Pretreatment on the Stability of Ascorbic Acid Complexes with Various Iron Sources in a Wheat Flake Cereal

“…All samples were analyzed in duplicate for total iron, elemental iron, total nonelemental, total soluble, insoluble nonelemental, soluble complexed, total ionic and ferrous and ferric iron according to a modification of the method of Lee and Clydesdale (1979) as described by Rizk and Clydesdale (1983). It should be noted that ionic iron is actually bathophenanthroline reactive iron and may include some soluble complexed iron for the reasons discussed previously by Clydesdale and Nadeau (I 984).…”