Formation mechanism and environmental stability of whey protein isolate-zein core-shell complex nanoparticles using the pH-shifting method

The alcohol-free pH-shifting method was applied to fabricate stable complex nanoparticles from hydrophilic whey protein isolate (WPI) and hydrophobic zein, which was aimed to develop a strategy to obtain desirable physicochemical stability. When the mass ratio of WPI and zein was elevated from 9:1 to 1:1, the size of WPI-zein complex nanoparticles was increased from 90 to 150 nm. The complex nanoparticle showed desirable storage stability (28 days) and physical stability, as well as excellent stability against various environmental stresses (heat, pH and ionic strength). The analysis of FTIR and the nanoparticle dissociation test revealed that hydrophobic effects and electrostatic attraction played an important role in the formation of WPI-zein complex nanoparticles. The transmission electron microscope (TEM) images evidenced the core-shell structure of WPI-zein complex nanoparticles with a regular spherical shape. The findings showed the feasibility of the simple pH-shifting method to fabricate the protein-based complex nanoparticles, which were expected to be further applied in the delivery of bioactive compounds.