Effect of pH and Ascorbic Acid on Iron Valence in Model Systems and in Foods

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Abstract
The effect of pH and ascorbic acid on the ionization and valence state of iron was investigated. Elemental iron, ferrous sulfate, ferric ortho phosphate, and sodium ferric EDTA were added, with and without ascorbate, 10 phthalate buffers of pH 2.7, 4.2, and 6.2. Total ionic, ferrous and ferric iron were analyzed by the bathophenanthroline method. A 4‐wk study showed the greatest amount of ionization and conversion to the ferrous valence occurring at pH 2.7, the least at pH 6.2. Ascorbic acid aided ionization at all pH values and favored the ferrous valence state at pH 2.7. Actual percent ionization and conversion to the ferrous valence in foods were compared to predictions derived from the model systems. The chemical changes of iron added to cranberry juice, tomato juice, and a chemically leavened biscuit dough followed the same trends observed in the phthalate buffers. Though not quantitatively, pH can be used to predict trends of chemical changes in iron added to foods.