Entrapment of curcumin in soy protein isolate using the pH-driven method: Nanoencapsulation and formation mechanism

The use of curcumin in the food industry is constrained by its poor aqueous dispersibility and instability. Previous studies have shown that stable curcumin nanoparticles can be prepared using a pH-driven method. In this study, the nanoencapsulation of curcumin by soybean protein isolate (SPI) was achieved using the pH-driven method. The effect of final pH on SPI and SPI-curcumin (SPI-Cur) nanocomposites was determined by analyzing the encapsulation efficiency and stability. SPI had a high encapsulation efficiency for curcumin and was stable, especially at pH 7 and 8. The formation mechanisms of SPI and SPI-Cur were further determined by molecular docking and multispectral analyses. The results showed that hydrogen bond acceptors (O−) of curcumin under alkaline media interacted with the donor groups (N–H) of amino acids to form hydrogen bonds. Throughout the process, hydrophobic interactions promoted the formation of the nanocomposites, and curcumin had a strong static fluorescence quenching effect on SPI. Furthermore, CD spectroscopy demonstrated that the pH-driven method altered the secondary structure of the SPI. This study provides evidence for the interaction mechanism between curcumin and SPI at different pH-driven stages and indicates SPI-Cur can be used as a delivery system of hydrophobic nutraceuticals.