Walnut protein–curcumin complexes: fabrication, structural characterization, antioxidant properties, and in vitro anticancer activity

In this study, walnut protein was employed as a novel carrier for the encapsulation of curcumin as a bioactive molecule using the solvent-free basic pH-shifting method. The encapsulation parameters (encapsulation efficiency and loading amount), the structural properties, reducing power, free radical (ABTS and DPPH) scavenging activity, and in vitro release behavior of samples were investigated. Moreover, the in vitro activities of curcumin-containing samples against proliferation of metastasis and non-metastasis human breast cancer cell lines (MDA-MB-231 and MCF-7, respectively) were evaluated. Fluorescence measurements revealed that the hydrophobic interactions were the main interactions among curcumin and walnut proteins. Fourier transform infrared analysis and circular dichroism spectroscopy also showed that the chemical structure of walnut proteins was not significantly affected through the complexation with curcumin. The results also showed that the encapsulation of curcumin by pH-driven method into walnut proteins, not only improved its water solubility and antioxidant activity besides sustained release behavior in simulated gastrointestinal condition of body, but also provided an effective sample which can inhibit the growth of breast cancer cell lines. The results indicate that the walnut protein could be used as a promising delivery system for water-insoluble bioactive compounds in the pharmaceutical and functional foods applications.