Fabrication of self-assembled zein nanoparticles via microfluidic chip and ultrasonic treatment

There are many health-promoting and disease-preventing bioactive compounds that are beneficial for human health, such as curcumin, lycopene, lutein, resveratrol, and apigenin. However, these bioactive compounds have some challenges to be used in the food and pharmaceutical industries because of their poor solubility, poor bioavailability, and chemical instability. These limitations can be overcome by encapsulating bioactive compounds into the nanoscale delivery systems (emulsions, liposomes, nanoemulsions, microgels, and nanoparticles). Among these nanoscale delivery systems, nanoparticles have received increasing attention in the food industry for applications like food packaging, sensor, and encapsulation. Zein is a group of prolamines extracted from corn, which is generally recognized as safe in the food industry, and it can form self-assembled nanoparticles in water or a low concentration of ethanol via anti-solvent precipitation. The traditional method to form the zein nanoparticles is dropping the zein ethanol solution into a bulk water phase with mechanical shearing, which creates the heterogeneous shear environment and uncontrolled for nanoparticle formation. In this study, two methods were used to fabricate zein nanoparticles: microfluidic chip and ultrasonic treatment. Microfluidic chips are novel platforms that are used to control the ultra-small volume of fluids going through channels with the dimensions of tens of micrometers. Ultrasound technology has been used in the food industry for many years for bio-compounds extraction, viscosity modification. The overall objective of this study is to assess the impact of process parameters on the properties of the zein nanoparticles formed via a microfluidic fabrication and ultrasonic treatment and to assess the encapsulation and activities of bioactive compounds, such as nisin and curcumin, in the zein nanoparticles. First, zein-OSA modified starch nanoparticles were fabricated via a T-junction configuration of the microfluidic chip. The dispersed phase was 1% or 2% zein in 70% (w/v) ethanol and the continuous phase was OSA-modified starch solution at various concentrations: 0%, 1%, 2.5%, 5%, 7.5%, and 10% (w/w). Compared with zein nanoparticles, the zein-OSA starch nanoparticle complexes were stable in various sodium chloride concentrations. Then, nisin was encapsulated into zein-OSA modified starch and the encapsulation efficiency and the anti-microbial activity of nisin in the zein nanoparticles against Listeria monocytogenes in Queso Fresco were measured. As the concentration of OSA modified starch increased, the encapsulation efficiency and anti-microbial activity of nisin increased. Zein nanoparticles were also formed via ultrasonic treatment with the different initial concentrations of ethanol in the continuous phase, the different ratios of the dispersed phase to continuous phase, and the different ultrasound amplitude. As the initial concentration of ethanol in the continuous phase increased, the particle size increased. PDI results revealed that as the concentration of ethanol in the continuous increased, the PDI decreased and then increased suggesting that there may be a critical ethanol concentration for zein seld-assembly. Finally, the curcumin was encapsulated into zein nanoparticles via ultrasonic treatment with different initial concentrations of ethanol in the continuous phase and ultrasound amplitude. The findings from this study showed that the presence of zein protected curcumin from degradation under heat and UV light environment, and encapsulation altered the physical state of curcumin from a crystallized state to an amorphous state which may improve the bioaccessibility of the curcumin