“Despite the broad studies of iron bioaccessibility and absorption to develop food supplements and fortificants, there is not enough information regarding the quantitative solubility of ferric pyrophosphate powder (FePP) as a function of pH and also in the presence of other ions,” the researchers wrote in their study published in Food Chemistry.
They observed the equilibrium solubility of FePP under different pH conditions similar to the human gastro-intestinal tract, as well as the effects of excess pyrophosphate ions on solubility at different pH values.
Prepping the solution
For this study, funded by Senter Novem and the Food Nutrition Delta Program, the scientists used FePP with an average size of 2.5 μm, according to supplier specification, from Dr. Paul Lohmann GmbH.
Other mixture ingredients, tetrasodium pyrophosphate, iron (III) chloride, acetic acid, sodium acetate, ammonium acetate, and Ferene S were purchased from Sigma-Aldrich.
The mixture for analysis is composed of 0.1 g FePP with 10 ml of deionised water, with differing amounts of tetrasodium pyrophosphate added in to stimulate different pH balances. Samples were kept at room temperature, and after one week, the pH of each sample was measured. Then, one ml of every sample was added to a centrifuge tube and the supernatant was collected to measure the dissolved iron concentration for 10 minutes.
Two methods of evaluation were used: Ultraviolet-visible spectroscopy (UV-vis) and inductively couples plasma atomic emission spectroscopy (ICP).
They found that iron had the highes solubility at a low pH. But between pH 7 and 8, the solubility increases again to 5 mM, “providing an opportunity for targeted release at the pH of the small intestine,” the researchers said.
“This is valuable information because it provides the framework for iron fortification and iron-functionalized edible composites passing through the gastrointestinal tract,” they added. “This low solubility will be a rate limiting step in determining the bioavailability of iron from FePP.”
Future studies, and future uses
Researchers observed that pyrophosphate ions participate in the ion transfer processes. These ions, as chelating agents, would release iron from transferrin and form a ferric pyrophosphate complex, and that pyrophosphate alone has the ability to mediate iron exchange from transferring to ferritin.
“The ability of iron to form a soluble complex in physiologically relevant pH for iron absorption, in combination with possible role of pyrophosphate in iron transfer, provides a very exciting opportunity to optimising iron absorption,” they wrote.
They argued that “the increased solubility of FePP at pH values close to the ones encountered in the small intestine is expected to enhance iron bioavailability exactly at the point of iron absorption.”
The findings still need to be tested out in in vivo studies, they added, and the results can also guide further research using in vitro cell experiments and clinical studies on iron bioavailability.