Iron/zinc Alginates as Vehicles for Food Fortification with Enhanced Stability in Polyphenol-Rich Foods

Food fortification with iron (Fe) and zinc (Zn) can effectively reduce deficiencies of these important micronutrients, but the reactivity of bioavailable Fe compounds in foods remains a challenge. Here, this problem was tackled by binding water-soluble Fe³⁺ and Zn²⁺ sources to alginate by ionotropic gelation, resulting in the formation of mixed Fe/Zn alginate beads. The dry beads were 0.8–1.4 mm in diameter and had Fe and Zn contents of up to 143 mg/g. Fourier transform infrared (FTIR) spectroscopy confirmed the successful binding of Fe³⁺ and Zn²⁺ with the carboxylic acid groups of alginate with preferential binding of Fe³⁺ over Zn²⁺. When added to difficult-to-fortify polyphenol-rich foods, the Fe alginate beads caused smaller color changes than water-soluble Fe sources, confirming that binding Fe³⁺ to alginate reduced its reactivity and improved its stability. Adding increasing amounts of Zn into the beads further improved color stability as evidenced by the lower ΔE values. The in vitro Fe solubility was 75–90% within 120 min at pH 1.0, independent of the Zn content, suggesting that the Fe from these structures is released in the stomach and available for absorption in the intestine. Their improved stability may make these Fe/Zn alginates attractive dual fortificants for difficult-to-fortify foods.