Construction of Double Emulsions Stabilized by Cyclodextrin Ester/Lecithin for Co-delivery of Curcumin and Proanthocyanidins

To fabricate stable double emulsions for co-encapsulating functional compounds, octenyl succinic β-cyclodextrin ester (OS-β-CD) was synthesized via esterification of β-cyclodextrin with octenyl succinic anhydride, and its structure was characterized. W₁/O/W₂ double emulsions were prepared using OS-β-CD and lecithin (LEC) as emulsifiers. A comprehensive assessment was performed on the stability and rheological characteristics of double emulsions, followed by an investigation of their encapsulation efficiency and release behavior for curcumin and proanthocyanidins. Fourier transform infrared (FTIR) spectroscopy and ¹H NMR spectroscopy confirmed the successful synthesis of OS-β-CD, through the introduction of new functional groups. The modified OS-β-CD exhibited reduced particle size and increased absolute zeta potential. The W/O/W double emulsions prepared with OS-β-CD of the substitution degree 0.0076 at 1% (w/v) in W₂ phase, 0.5%(w/v) OS-β-CD in W₁ phase, 2% (w/v) LEC in oil phase, W₁:O volume ratio of 3:7, and W₁/O/W₂ ratio of 1:1 exhibited maximum apparent viscosity and storage modulus along with optimal emulsification stability. Confocal laser scanning microscopy analysis revealed that double emulsions have a well-defined two-membrane, three-phase compartmental structure. The double emulsion prepared under optimal conditions exhibited good thermal stability after the co-loading of proanthocyanidins and curcumin. Even after storage for five days at 37 °C, the emulsification index remained as high as 90%. This system effectively delivered curcumin and proanthocyanidins together. Compared to emulsions loaded with a single component, the W_pac/O_cur/W emulsion significantly improved the retention rate of proanthocyanidins to 56.65% at 37°C, indicating a synergistic stabilization effect between the two components. Meanwhile, the co-delivered double emulsion exhibited DPPH and ABTS radical scavenging rates of 90.02% and 87.69%, respectively, significantly higher than those of mixtures of free curcumin and proanthocyanidins. In vitro simulated gastrointestinal release results revealed that the W_pac/O_cur/W emulsion enhanced curcumin release by 11.34%, compared to the W/O_cur/W emulsion. The W_pac/O/W emulsion showed a low release rate of proanthocyanidins in simulated gastric fluid, but its final release rate in simulated intestinal fluid was similar to that of the W_pac/O_cur/W system. This study confirms the potential of cyclodextrin ester/lecithin-stabilized double emulsions for co-delivery of functional compounds, providing both theoretical foundations and technical support for related research.