Utilization of multilayer-technology to enhance encapsulation efficiency and osmotic gradient tolerance of iron-loaded W1/O/W2 emulsions: Saponin-chitosan coatings

Abstract

Multilayer technology was used to improve the performance of multiple emulsions. W1/O/W2 emulsions were fabricated using 2 wt% polyglycerol polyricinoleate (PGPR) as a hydrophobic surfactant and 2 wt% saponin as a hydrophilic surfactant. The anionic saponin-coated W1/O droplets in the multiple emulsions were coated with a layer of cationic chitosan using electrostatic deposition. The influence of chitosan concentration (0.05–0.4 wt%) on the formation and stabilization of the W1/O/W2 emulsions was evaluated by measuring the ζ-potential, microstructure, and mean droplet diameter. The W1/O droplets became saturated at 0.3 wt% chitosan, which resulted in emulsions containing relatively small cationic droplets (d ≈ 400 nm; ζ ≈ +30 mV) that were resistant to droplet aggregation. The double-layer W1/O/W2 emulsions were highly effective at retaining iron (ferrous sulfate) within their internal aqueous phase, with more than 87% remaining after storage for 28 days at 25 °C. They also remained stable when exposed to an osmotic stress gradient, which was created by having different glucose levels (3–30 wt%) in the external aqueous phases, but a constant level (30 wt%) in the internal aqueous phase. The size of the saponin-chitosan coated W1/O droplets was unchanged from 30 to 6 wt% glucose in the external aqueous phase, while the saponin-coated ones were only stable from 30 to 21 wt% glucose. The chitosan coatings also inhibited the release of iron from the W1/O/W2 emulsions under osmotic stress. Overall, our results suggest that double-layer W1/O/W2 emulsions may be effective iron delivery systems for food applications.