Fabrication of zein-modified starch nanoparticle complexes via microfluidic chip and encapsulation of nisin

A microfluidic chip is a micro-reactor that precisely manipulates and controls fluids. Zein is a group of prolamines extracted from corn that can form self-assembled nanoparticles in water or a low concentration of ethanol in a microfluidic chip. However, the zein nanoparticles have stability issues, especially in a neutral pH environment due to the proximity of the isoelectric point. This study was designed 1) to evaluate the effect of octenyl succinic anhydride (OSA) modified starch on the stability of zein nanoparticles formed using a microfluidic chip and 2) to apply the zein-OSA starch for encapsulation of nisin and evaluate its anti-microbial activity in a model food matrix. A T-junction configuration of the microfluidic chip was used to fabricate the zein nanoparticles using 1% or 2% zein solution and 0-10% (w/w) of OSA starch solution. The stability of the nanoparticles in various ionic strength environments was assessed. Encapsulation efficiency and anti-microbial activity of nisin in the zein nanoparticles against Listeria monocytogenes in a fresh cheese were measured. As the concentration of OSA starch increased from 0 to 10%, effective diameter increased from 117.8 ± 14.5 to 198.7 ± 13.9 nm without affecting polydispersity indexes and zeta-potential changed toward that of the modified starch indicating the zein surface coverage by the OSA starch. The zein-OSA starch nanoparticle complexes were more stable at various sodium chloride concentrations than the zein nanoparticles without OSA starch. The encapsulation efficiency of nisin was positively correlated with the OSA starch concentration. The anti-microbial activity of nisin in the fresh cheese also increased until 3-days of storage as the concentration of the OSA starch increased, which presented both a potential and challenge toward applications.