Encapsulation of quercetin in pullulan-coated zein nanoparticles

Quercetin (Que), a natural flavonoid with high antioxidant activity, exhibits limited application in aqueous systems due to its poor water solubility and instability. To address these limitations, this study developed and characterized zein-pullulan composite nanoparticles for the encapsulation and protection of Que. Zein nanoparticles (Z NPs) and Que-loaded zein nanoparticles (ZQ NPs) were first prepared via antisolvent-induced self-assembly, employing hydrophobic interactions and hydrogen bonding. Subsequently, pullulan (PUL), a hydrophilic and biodegradable polysaccharide, was deposited onto the surface of Z NPs and ZQ NPs through electrostatic interaction to form ZP NPs and ZQP NPs. The optimized ZQP NPs exhibited a core-shell structure with high encapsulation efficiency and spherical morphology. Surface coating with PUL significantly enhanced the hydrophilicity of the nanoparticles, as confirmed by water contact angle measurements, and also enhanced their thermal and storage stability. After 12 days of storage at 4 °C, ZQP NPs maintained the highest Que retention rate of 88.10 ± 0.16%. Additionally, both ZQ NPs and ZQP NPs showed strong antioxidant ability. These results demonstrate that zein-pullulan composite nanoparticles are a promising antioxidant delivery system, offering both protection and aqueous compatibility for hydrophobic bioactives, and suggesting great potential for incorporation into water-soluble antioxidant films.