Soy protein isolate (SPI)-hemin complex nanoparticles as a novel water-soluble iron-fortifier: Fabrication, formation mechanism and in vitro bioavailability

Hemin is recognized as a superior biological iron-fortifier in the prevention and treatment of iron deficiency anemia. Nevertheless, free hemin could have low bioavailability due to its insolubility in intestinal fluid after passing through the digestive tract, so hemin as a direct fortifier is not as effective as it should be. In this study, a novel hemin-delivery system with good water-solubility was developed by fabricating soy protein isolate (SPI)-hemin complex nanoparticles through pH-driven method, and the formation mechanism and bioavailability were also investigated. Hemin could bind to SPI and form nanoparticles with a diameter ranging from 100 to 300 nm in the process of pH dropping from 12.0 to 7.0, and thereby significantly improve the water-solubility of hemin. It was proved that the nanoparticles were produced mainly through hydrophobic interaction between SPI and hemin, and driven by entropy. The results from in vitro simulated gastrointestinal digestion experiments indicated that bioavailability of hemin was also significantly improved (P < 0.05), and the value in SPI-hemin nanoparticles reached nearly 80% at the concentrations of 1.0% (w/v) SPI and 0.25% (w/v) hemin. SPI-hemin nanoparticles could be an innovation for improving the solubility and bioavailability of hemin and an easily acceptable candidate for the design of novel iron-fortified foods.