One-step self-assembly of curcumin-loaded zein/sophorolipid nanoparticles: physicochemical stability, redispersibility, solubility and bioaccessibility

Curcumin, a polyphenolic compound isolated from turmeric, exhibits various biological activities. The application of this nutraceutical in foods, however, is limited due to its extreme hydrophobicity, inferior stability, and poor bioaccessibility. The purpose of this paper is to prepare alcohol-free curcumin-loaded zein/sophorolipid nanoparticles (Cur-Z/SNPs) by one-step self-assembly to overcome the abovementioned challenges of curcumin. In detail, Cur-Z/SNPs were formed by mixing curcumin, zein, and sophorolipid under neutral conditions without any organic reagents or high energy equipment. The encapsulation efficiency and loading capacity of Cur-Z/SNPs were 94.08% and 11.50%, respectively. The spherical shape of Cur-Z/SNPs was observed by using a transmission electron microscope. The self-assembly mechanism involved hydrogen bonding, hydrophobic and electrostatic interactions, and the crystalline nature of curcumin changed to amorphous during self-assembly. Cur-Z/SNPs enhanced the zein denaturation resistance. They exhibited complete redispersibility and improved the aqueous solubility by approximately 246 times compared with free curcumin. The fresh Cur-Z/SNPs exhibited physicochemical stability at pH 5.0-8.0, ionic strength within 250 mM, and storage at 25 °C and 4 °C for 30 days. Notably, Cur-Z/SNPs could achieve excellent storage stability at room temperature as compared to those at refrigeration. Furthermore, lyophilization had a positive effect on storage stability, did not change the pH stability, and slightly reduced the ionic strength stability. Besides, Cur-Z/SNPs increased the 1,1-diphenyl-2-picrylhydrazyl free radical (DPPH˙) scavenging capacity compared to free curcumin. The bioaccessibility of curcumin was increased by about 6 times by Cur-Z/SNPs. These findings provided new insight into the application of hydrophobic nutrients in alcohol-free functional foods.