Formation and characterization of hollow particles with zein-WPI hybrid shell for curcumin encapsulation

Hollow particles contain the inner aqueous compartment surrounding by a shell layer. Controllable construction of the shell layer may improve the potential use of hollow particles for encapsulating polyphenols. In this study, a novel method with alkaline-heat treatment was developed to fabricate the hollow particles with a hybrid shell of zein and whey protein isolate (WPI). Hollow particles were characterized in terms of soluble proteins, size distribution, ζ-potential, hollow structure and shell hydrophobicity. WPI at 0.25% (w/v) was enough to stabilize its zein complex hollow particles at neutral condition. The size of zein-WPI hollow particles was respectively 90 and 198 nm at pH 11 and 7, with a greater portion of proteins participated in the formation of hollow particles at pH 7 than 11. The formation mechanism of hollow particles was analyzed in terms of circular dichroism, infrared spectroscopy, dissociation test, gel electrophoresis, sulfhydryl contents and amino acid analysis. Hydrophobic interactions played a dominant role in stabilizing the shell structure of zein-WPI hollow particles, while Cys, Tyr and Lys participated in the covalent interaction between zein and WPI in hollow particles. Moreover, the shell hydrophobicity decreased by the presence of WPI, which provided a suitable microenvironment for the encapsulation of curcumin at pH 7. The findings of this study shed light on the design of protein-based hollow particles for the delivery of bioactive compounds.