Application of starch nanoparticles as a stabilizer for Pickering emulsions: Effect of environmental factors and approach for enhancing its storage stability

Abstract

To apply starch nanoparticles (SNPs) as a Pickering emulsion stabilizers, effect of environmental factors (pH and ionic strength) on the characteristics of SNPs was evaluated. The SNPs were characterized by zeta-potential measurement, dynamic light scattering, and transmission electron microscopy (TEM). As the pH value (from 4 to 10) of medium decreased or NaCl concentration (from 0 to 60 mM) of medium increased, the hydrodynamic mean diameter of SNPs was increased. The TEM results revealed that the larger hydrodynamic mean diameter of SNPs resulted from aggregation of SNPs. Higher SNPs content decrease the droplet size of the Pickering emulsion and, it is thought that SNPs content higher than 5% may be required to produce a stable emulsion with 10% oil content. Oiling-off on top of the emulsion clearly appeared at higher pH conditions. Stability of the emulsion was enhanced as pH decreased, and oiling-off was not observed during the storage at pH 3. Addition of chitosan (>0.4%) enhanced the stability of the emulsion without any oiling-off and creaming during the storage at pH 7. Confocal laser scanning microscopy revealed that chitosan may form a stable solid layer with SNPs surrounding the emulsion, which may enhance stability of the emulsion. The findings in this study suggested a useful information and approach for application of SNPs as Pickering emulsion stabilizers in various industries.