Dissolution behaviour of ferric pyrophosphate and its mixtures with soluble pyrophosphates: Potential strategy for increasing iron bioavailability

• Excess of pyrophosphate ions strongly increases the solubility of ferric pyrophosphate at pH 5–8.5.
• The increase in solubility is attributed to formation of soluble complexes between Fe (III) and pyrophosphate ions.
• The ~10 fold increase in the concentration of ionic iron at pH 7–8.5, which is close to the one of the small intestine, is expected to be beneficial for enhancing iron bioavailability.

Ferric pyrophosphate (FePP) is a widely used iron source in food fortification and in nutritional supplements, due to its white colour, that is very uncommon for insoluble Fe salts. Although its dissolution is an important determinant of Fe adsorption in human body, the solubility characteristics of FePP are complex and not well understood. This report is a study on the solubility of FePP as a function of pH and excess of pyrophosphate ions. FePP powder is sparingly soluble in the pH range of 3–6 but slightly soluble at pH < 2 and pH > 8. In the presence of pyrophosphate ions the solubility of FePP strongly increases at pH 5–8.5 due to formation a soluble complex between Fe(III) and pyrophosphate ions, which leads to an 8–10-fold increase in the total ionic iron concentration. This finding is beneficial for enhancing iron bioavailability, which important for the design of fortified food, beverages, and nutraceutical products.