Bi-layered oil encapsulates formed by polydopamine-supported in situ complex coacervation: Investigation of structure formation and sustained release performance

In polydopamine (PDA)-supported in situ complex coacervation, PDA is pre-coated onto emulsion droplets, and further applied as an interlayer to support the interfacial immobilization of coacervates biopolymers. In the current research, the stepwise immobilization of gelatin (GE) and gum Arabic (GA) onto PDA layer is monitored to in-depth investigate the mechanism of PDA layer as coating material and functional substrates. GE and GA were applied as adsorbates, with different forms of PDA (spherical shell, planar solid, and nanoparticles) as substrates. Real-time observations of the binding steps were performed using quartz crystal monitor with dissipation (QCM-D) and isothermal titration calorimetry (ITC). Meanwhile, using PDA-supported coacervates as encapsulating material, sustained release of essential oil volatiles was also evaluated, either dispersed in detergent solution or freeze dried in open air. The anti-oxidation performance was determined by measuring the absorbance of lipid hydroperoxide using UV spectrophotometer. The results revealed that PDA enabled synergistic immobilization of biopolymers through chemical bonding and adhesive force during the processing of in situ complex coacervation, thus enhanced protection of core compounds with two-stage releasing kinetics and prevented hyperoxidation. Also, PDA-based colloids and substrates also exhibit controllable conformation characteristic, provide a promising prospect as versatile intermediate functional biomaterials for encapsulation.