Facile preparation of zein nanoparticles with tunable surface hydrophobicity and excellent colloidal stability

Herein, zein nanoparticles (ZNPs) were prepared by a general and simple method through the combination of pH pretreatment and antisolvent precipitation. The resultant ZNPs have been extensively characterized by scanning electron microscopy, dynamic light scattering, fluorescence spectroscopy, zeta potential and contact angle measurements. It is worth noting that pH treatment of zein molecules can tune the surface property of the as-prepared ZNPs. Molecular zein pretreated under alkaline conditions yielded smaller nanoparticles, whereas those pretreated under acidic conditions produced larger nanoparticles. After the pretreatment with an alkaline solution, the surface of resultant ZNPs tended to be more hydrophilic. Importantly, the ZNPs prepared from zein molecules that were pretreated at neutral or alkaline conditions had better colloidal stability and re-dispersibility (after freeze-drying). In addition, a highly stable Pickering emulsion was gained using the as-prepared ZNPs under neutral condition. This work offers a facile approach to the fabrication of ZNPs with a tunable surface hydrophobicity and excellent colloidal stability, which are beneficial for their application in encapsulation systems and other fields.