Formulation and characterization of curcumin-loaded microemulsions: Evaluation of antioxidant stability and in vitro release

•The O/W and W/O/W microemulsion curcumin-loaded were synthesized.•The synthesized microemulsion is a spherical droplet with a particle size of 10–20 nm.•The encapsulation mechanism of curcumin in microemulsions was probed.•In vitro release indicated a sustained release of curcumin from microemulsion.•The solubility and antioxidant ability of curcumin were enhanced. In this study, oil-in-water (O/W) and water-in-oil-in-water (W/O/W) microemulsions (MEs) were synthesized as the carrier for curcumin delivery as a means to improve water solubility and antioxidative stability. MEs were characterized by measuring particle size, polydispersity index (PDI), transmission electron microscope, viscosity, and electrical conductivity. Furthermore, the position of curcumin in MEs was probed by proton nuclear magnetic resonance spectroscopy (1H NMR), and MEs antioxidant capacity and in vitro release of curcumin were investigated. Curcumin-loaded MEs were constituted of spherical droplets with a mean particle size of 10.0–20.0 nm and PDI of 0.2–0.3. 1H NMR confirmed that curcumin is embedded in the inner structure of MEs. Collectively, MEs synthesized in this study were shown to extremely improve solubility of curcumin. Furthermore, assessment of in vitro release and storage stability of the two experimentally-synthesized MEs showed that W/O/W ME had greater sustained release and antioxidant activity compared to O/W ME. No significant differences between storage at 4 °C and 25 °C were observed for the two evaluated ME. Our work illustrated that O/W and W/O/W MEs were well qualified for the delivery of curcumin.