Heat-Induced Formation of Soy Protein Nanoparticles at Acidic pH for Encapsulation of Curcumin

In the present study, soy protein isolate (SPI) was subjected to static heat treatment (95℃ for 30 min) under specific pH conditions (pH 7.0 and 5.9) to form nanoparticles through self-assembly, designated as HSPI and HSPI (pH 5.9), respectively. The influence of homogenization and sonication was comparatively investigated on the encapsulation of curcumin as a hydrophobic active ingredient into protein nanoparticles. Results from fluorescence spectroscopy showed that hydrophobic interactions between SPI, HSPI and HSPI (pH 5.9) and curcumin caused fluorescence quenching of the protein and improved the water dispersibility of curcumin. Herein, heat treatment increased the protein surface hydrophobicity and particularly promoted the formation of particles with uniformed size distribution (PDI < 0.2) at pH 5.9, noticeably enhancing the protein-curcumin interactions. Homogenization and sonication promoted the encapsulation of curcumin into SPI, HSPI and HSPI (pH 5.9) upon driven by hydrophobic forces, and the effect of the latter was more pronounced. Moreover, when compared with SPI and HSPI, the core-shell structure of HSPI (pH 5.9) facilitated its co-assembly with curcumin during sonication, forming stable nanoparticles with uniformed size distribution, which significantly improved the water solubility and storage stability of curcumin. © 2020, China Food Publishing Company. All right reserved.