A bilayer emulsion gel stabilized by succinylated whey protein isolate and chitosan for delivering curcumin: Characterization, stability, and digestive properties

This study developed a bilayer emulsion gel using complexes of succinylated whey protein isolate (SWPI) and chitosan (CS) (termed HCS), primarily characterizing its structure, stability, and digestion properties, with curcumin delivery as a model application. Molecular docking revealed succinylation increased SWPI-CS binding sites and affinity improvement. The HCS emulsions exhibited pH/ionic-dependent stability, achieving optimal performance at pH 4 and 160 mM NaCl. Fluorescence imaging validated a trilaminar interface (outer CS layer/inner SWPI layer/oil core). Subsequent experiments incorporating curcumin demonstrated oxidative protection (90 % curcumin retention at 24 h) and digestion resistance (37.5 % bioaccessibility). Rheology demonstrated gelation (G′ > G″) at φ  ≥ 0.4, with NaCl strengthening the network. In vitro digestion showed HCS-E gastric resistance (pepsin shielding by CS) and controlled intestinal release (2-fold slower FFA hydrolysis vs. single-layer emulsions). The bilayer design synergistically combines SWPI's emulsification with CS's steric hindrance, offering a platform for bioactive delivery.