Interaction of iron(III) with taste enhancers: Potential of Fe(III) salts with inosine monophosphate or guanosine monophosphate for food fortification

Iron interactions in iron-fortified savory concentrates lead to undesirable discoloration, even when poorly-water soluble iron salts such as ferric pyrophosphate (Fe₄PP₃) are used. This is the first study to comprehensively investigate the interaction of Fe(III) with three common taste enhancers: glutamate (Glu), inosine monophosphate (IMP), and guanosine monophosphate (GMP). The stability of the complexes of Fe(III) with IMP or GMP is higher compared to that with Glu. Neutrality of IMP or GMP species with Fe(III) at pH 3–8 resulted in precipitation. This property was exploited to synthesize Fe(III) salts of IMP or GMP (i.e. Fe₂IMP₃ and Fe₂GMP₃) by aqueous chemical precipitation. Iron dissolution from Fe₂IMP₃ and Fe₂GMP₃ was up to twenty-fold higher at gastric pH (1–3), indicative of better bio-accessibility, and up to fifteen-fold lower at food pH (3–7), indicative of decreased reactivity in food, compared to Fe₄PP₃. Consequently, Fe₂IMP₃ and Fe₂GMP₃, compared to Fe₄PP₃, led to less discoloration in combination with the poorly soluble phenolics that are commonly present in savory concentrates. We conclude that Fe(III) salts of IMP or GMP can potentially serve as iron fortificants due to their increased solubility at gastric pH (1–3), decreased iron dissolution at food pH (3–7), and decreased reactivity at food pH.