Electrostatic deposition of polysaccharide onto soft protein colloidal particles: Enhanced rigidity and potential application as Pickering emulsifiers

Abstract

The feasibility of utilizing β-lactoglobulin nanoparticles (β-lgNPs) as effective Pickering emulsifiers for stable emulsions always meets doubts since they are liable to undergo structural modifications upon adsorption at oil/water interface. In this work, we fabricated β-lactoglobulin-based composite particles with desirable properties as Pickering stabilizers via electrostatic deposition. Through optimizing the propylene glycol alginate (PGA) concentration, uniform β-lg-PGA composite nanoparticles (β-lgPNPs) with mean particle size of 276.6 nm and three-phase contact angle of 89.8 ± 0.3° were obtained at a β-lg-to-PGA mass ratio of 2:1. β-lgPNPs could barely reduce interfacial tension but facilitate the formation of a thick adsorption layer with thickness approximately equal to the hydrodynamic radius of β-lgPNPs around the droplet, sterically hindering close approach of the droplets. Circular dichroism study revealed that the adsorbed PGA molecules could effectively obstructe the denaturation of β-lgNPs at oil/water interface. With the increasing oil fraction, a greater gel strength and viscosity could be observed as determined by diffusing wave spectroscopy. Confocal laser scanning microscopy results indicated that the interfacial structure of oil droplets contained both β-lgNPs and PGA network, which jointly contributed to the stability of the emulsion gels. Results of this study will advance our understanding of utilizing soft protein based particles as particulate emulsifiers for the design and development of Pickering emulsions.