Preparation of highly-dispersed iron pyrophosphate nanoparticles via ultrasound-assistant carboxymethyl cellulose modification to enhance their liposome encapsulation and cell absorption.

Ferric pyrophosphate (FePP) is commonly used in fortified foods because of its subtle metallic odor/color. However, the insoluble nature of FePP restricts its intestinal absorption, thereby diminishing its efficacy. Liposomes can enhance the transmembrane absorption of encapsulated ingredients but encounter difficulties when encapsulating insoluble compounds. In this study, it was initially attempted to boost FePP solubility by reducing its particle size. Nevertheless, nanoscale FePP (N-FePP) exhibited a strong tendency to aggregate. To address this, an ultrasound-assisted carboxymethyl cellulose modification was innovatively proposed. This method effectively prevented N-FePP aggregation by increasing its charge density from -23 mV to -40 mV and decreasing surface tension of the N-FePP suspension from 71.1 mN/m to 43.8 mN/m. Consequently, the modified N-FePP (MN-FePP), with a particle size of 237 nm and excellent dispersion, was successfully obtained. The encapsulation efficiency of MN-FePP in liposomes (MN-FePP-Lip) was significantly enhanced compared to that of N-FePP (74.9 % vs. 27.8 %). Furthermore, in comparation with the unencapsulated MN-FePP, MN-FePP-Lip exhibited increased cellular absorption efficiency (intracellular iron concentrations of 171.54 μmol/L vs. 115.24 μmol/L) and total antioxidant levels (9.04 U/mg prot vs. 7.28 U/mg prot) in cells. Therefore, the MN-FePP-Lip developed in this study shows great potential as a novel iron fortifier.