W1/O/W2 double emulsions stabilized by natural diosgenin and ultrasound-treated pea protein nanoparticles: A plant-based system for iron fortification

This study developed and optimized a fully natural W1/O/W2 double emulsion system for oral iron delivery, using diosgenin, a natural triterpenoid saponin, to stabilize the inner water–oil (W1/O) interface and pea protein nanoparticles (PPNs) to stabilize the outer oil–water (O/W2) interface. The optimal primary emulsion, containing 9 % diosgenin in the oil phase and a W1:O ratio of 2:8, exhibited excellent centrifugal and storage stability. External aqueous phases (W2) were prepared from 2 %, 4 %, and 6 % pea protein dispersions, which underwent ultrasound treatment followed by centrifugation to produce corresponding PPNs suspensions designated as PPN-2 %, PPN-4 %, and PPN-6 %, respectively. The primary iron-containing W1/O emulsion was dispersed into these W2 phases at a W1/O: W2 ratio of 2:8, yielding stable W1/O/W2 emulsions with iron encapsulation efficiencies exceeding 99 %. In vitro simulated digestion revealed that the emulsions with PPN-6 % effectively minimized iron release in the gastric phase (<1 %) while promoting controlled release in the intestinal phase, thereby improving bioavailability and potentially reducing gastric irritation. Compared to synthetic PGPR-stabilized emulsions, the diosgenin-PPNs system demonstrated superior structural stability and digestive performance. This multilayered, food-grade emulsion system offers a promising, health-oriented alternative for iron fortification in functional foods.