Fat crystal-stabilized water-in-oil emulsions as controlled release systems

- Pickering W/O emulsions essentially prevented salt release from water droplets.
- Salt release increased with concentration from network-stabilized W/O emulsions.
- Salt transport through oil likely occurred through hydration/dehydration mechanism.
- The melting of the Pickering shell greatly increase salt release kinetics.
- Melting of network crystals did not influence salt release significantly.

Fat crystal-stabilized water-in-oil emulsions were developed as a controlled release matrix for the delivery of salt. Glycerol monostearate (GMS), glycerol monooleate (GMO) and polyglycerol polyricinoleate (PGPR) were used as emulsifiers and hydrogenated canola oil (HCO) was added as a solid fat. Salt release towards an external aqueous phase was measured via conductivity as a function of temperature. Following 2 h of release at room temperature, the GMS emulsion had the highest encapsulation efficiency followed by the PGPR-HCO, PGPR-only and GMO-HCO emulsions, respectively. The GMS crystals formed Pickering shells around the water droplets that effectively prevented salt transport whereas in the GMO-HCO emulsion, the presence of partial interfacial HCO crystal coverage resulted in lower retention. All crystal-stabilized emulsions showed rapid release of their salt load upon melting of the surrounding solid fat, while little temperature effect was observed with the PGPR-based emulsions. However, these emulsions were sensitive to the presence of a salt concentration gradient whereas the fat crystal-stabilized emulsions showed little response. Overall, this study demonstrated that the spatial distribution of the stabilizing fat crystals (i.e., interfacial vs. continuous phase) as well as the emulsifier type were critical factors controlling salt release patterns.