Iron fortification of foods: Multi-mineral pyrophosphate-based salts

Abstract

Iron deficiency is one of the most prevalent nutritional problems in the world. However, iron is a challenging mineral to add to food products. Iron-containing compounds can react with the (phyto)chemicals present in foods and as a result cause severe changes in the organoleptic properties, for instance off-flavor and off-color. To date, iron fortification of foods has proven to be an efficient and cost-effective approach to overcome iron deficiency. Iron-containing compounds that are applied as iron fortificants are divided into three main categories; water-soluble, poorly watersoluble (but soluble in dilute acid), and water-insoluble (and poorly soluble in dilute acid). Although water-soluble compounds have the advantage of high iron bioavailability, the other categories are more in the center of attention because of their minimum influence on the organoleptic properties of the foods which is a consequence of their limited solubilities. Among the poorly water-soluble or water-insoluble iron compounds, ferric pyrophosphate (Fe(III)PP) has attracted a great deal of attention. Fe(III)PP is a white solid that prevents addition of unwanted colors to foods. It has been shown that Fe(III)PP is very poorly soluble in the food relevant pH (3-7) which is the reason for the limited reactivity of this salt with the fortified food vehicle. Furthermore, Fe(III)PP has low solubility at low pH and enhanced dissolution at high pH which is advantageous for ensuring the sufficient iron bio-accessibility. However, it has previously been shown that addition of iron in the form of Fe(III)PP cannot fully prevent the discoloration of the phenolic-rich foods. Therefore, improving the function of Fe(III)PP as an iron fortificant (i.e., decreasing the iron-mediated reactivity while ensuring the iron bio-accessibility) still remains of interest. In this work, we seek the strategies by which we can design iron-containing compounds with minimum solubility in the food-relevant pH (3-7), and high and/or fast dissolution in gastric and intestinal pH (1-3 and 6-8, respectively). Interestingly, mother nature can help us find the answer. Inspired by naturally-occurring minerals such as anapaite (i.e., a mixed calcium–iron phosphate mineral), we intend to embed iron in the matrix of a second (divalent) metal (or mineral) salt, which is less chemically reactive, aiming for: (i) decreasing the iron-mediated reactivity to preserve the organoleptic properties of the food vehicle, and (ii) increasing iron dissolution from the designed multi-mineral salt in the gastric conditions to ensure bio-accessibility of iron (and the other mineral). Another benefit of using these multi-mineral salts is the possibility of simultaneous delivery of at least two minerals by the fortified food vehicle. In Part I of this thesis, we explore the possibilities of improving the function of Fe(III)PP as an iron-fortificant by mixing Ca along Fe in one salt matrix. Part II of the present thesis is dedicated to iron (II)-containing pyrophosphate salts that are potential iron fortificants. In this part we explore the possibility of applying ferrous pyrophosphate (Fe(II)PP) in food fortification. Finally, in Part III of this thesis, we challenge the notion that cooperative binding only happens in complicated biological systems like hemoglobin.