Design and characterization of Ca-Fe(III) pyrophosphate salts with tunable pH-dependent solubility for dual-fortification of foods

Food-fortification using poorly water-soluble mineral-containing compounds is a common approach to deliver iron. However, it comes with the challenge of ensuring iron bio-accessibility and limiting iron-phenolic interactions that can change organoleptic properties. Mixed Ca-Fe(III) pyrophosphate salts with the general formula Ca₂(_1-x)Fe_4x(P₂O₇)_(1+2x) were designed as a system for simultaneous delivery of iron and calcium. The salts were synthesized via a co-precipitation method and characterized by TEM-EDX, XRD, and FT-IR. All mixed salts with 0.14 ≤ x ≤ 0.35 yielded homogenous amorphous particles. The iron dissolution from these mixed salts showed a fourfold increase at gastric pH compared to Fe(III) pyrophosphate. In the food-relevant pH range, the salts with x ≤ 0.15 showed up to an eight-fold decrease in iron solubility. Despite this, reactivity of the mixed salts in tea was similar to that of FePP. Our results indicate that these mixed salts are potential dual-fortificants with tunable iron content and solubility.