Zein-quercetin covalent nanoparticles encapsulating oregano essential oil: Improved stability, antioxidant, and antibacterial properties

The zein-quercetin covalent complexes were prepared by alkali treatment (A-ZEIN-Q) and free radical grafting (R-ZEIN-Q) and subsequently followed by encapsulation of oregano essential oil (OEO), and alkali grafted zeinquercetin covalent nanoparticles (A-ZQNPs-OEO) and free radical grafted zein-quercetin covalent nanoparticles (R-ZQNPs-OEO) were synthesized respectively. Additionally, the particle size, zeta-potential, microstructure, encapsulation efficiency, release behaviour, surface hydrophobicity, stability, antioxidant activity, and antibacterial activity of these nanoparticles were characterized. The results of infrared spectroscopy showed that a covalent bond was formed between zein and quercetin, the particle size of the nanoparticles decreased, and the degree of densification was higher than that of zein nanoparticles. Unlike the aggregated zein nanoparticles, the zein-quercetin nanoparticles were dispersed more uniformly. In addition, the encapsulation efficiency of OEO in A-ZQNPs-OEO and R-ZQNPs-OEO increased significantly from 45.11 % to 73.42 % and 70.90 % to that of OEO in single zein nanoparticles, respectively. Among the four nanoparticles, A-ZQNPs-OEO shows the highest stability, while the OEO-encapsulated quercetin covalent nanoparticles show better-sustained release performance, lower surface hydrophobicity, and excellent antioxidant and antibacterial activities. Overall, the synthesized OEO encapsulated zein-quercetin covalent nanoparticles possess the ability to be applied in food preservation and other applications.