Fabrication of heat-treated soybean protein isolate-EGCG complex nanoparticle as a functional carrier for curcumin

In this study, soybean protein isolate (SPI) was first heat-treated to yield modified SPI (HSPI). Then SPI- and HSPI-epigallocatechin-3-gallate (EGCG) biopolymers (SPI-E and HSPI-E) were fabricated using an alkali covalent crosslinking method and their abilities to function as novel delivery carriers to load curcumin (Cur) were investigated. The particle size of loaded-Cur SPI-E and HSPI-E complex nanoparticles (SPI-E-C and HSPI-E-C) were all reduced and the zeta-potentials were all negative. FTIR and fluorescence spectra analysis indicated the presence of hydrogen bondings, hydrophobic interactions, and electrostatic interactions were the driving force for the formation of the carrier-Cur complex. Moreover, compared with SPI-E, HSPI-E had a high loading rate of Cur, improved bioaccessibility and scavenging capacity, smaller size, thinner sheet shape morphology, and stronger binding affinity. In its protective capacity as a delivery carrier, HSPI-E significantly improved the thermal stability, acid stability and controlled release characteristics of Cur, thereby overcoming the instability of a single protein carrier and possessing superior properties. These findings indicate that the HSPI-E polymer is a favorable carrier for delivering Cur and suit for development as a delivery polymer carrier to protect hydrophobic nutraceuticals and drugs with high-loading rate-performance and health-related functions without the use of crosslinkers.