Kafirin nanoparticles-stabilized Pickering emulsions: Microstructure and rheological behavior

Abstract

Kafirin, the prolamin protein from sorghum, was fabricated into spherical nanoparticles and then introduced as a fully natural interfacial stabilizer for Pickering emulsions. Kafirin nanoparticles produced via anti-solvent precipitation method exhibited water over oil wetting preference. The resultant oil-in-water emulsions exhibited resistance against coalescence with internal oil phase fraction ranging from 58.8% to 78.6%. Emulsion droplet size distribution and rheological properties of emulsions stabilized by kafirin particles were influenced by the applied particle concentration, oil fraction and ionic strength in aqueous phase. Basic trends included: increasing particle concentration in aqueous phase led to increase in emulsified phase volume, decrease in oil droplet sizes and increase in storage moduli for the viscoelastic responses; As oil phase fraction increased, the emulsified phase volume fraction and droplet size increased, and the rheological properties shifted from fluid dominant to elastic dominant. The addition of salt in aqueous phase promoted the migration process and lifted the stiffness of gel-like emulsions. Cryo-scanning electron microscopy (cryo-SEM) and optical microscopy under fluorescence field evidenced the attachment of kafirin particles on oil-water interface. Overall, kafirin nanoparticles offer promising prospects in fulfilling the demands of “surfactant-free” emulsions with tunable characteristics.