Protein Nanocage as a pH-Switchable Pickering Emulsifier

Encapsulation of active compounds in Pickering emulsions using bioderived protein-based stabilizers holds potential for the development of novel formulations in the fields of foods and cosmetics. We employ a dodecahedron hollow protein nanocage as a pH-switchable Pickering emulsifier. E2 protein nanocages are derived from pyruvate dehydrogenase multienzyme complex from Geobacillus stearothermophilus which adsorb at the oil/water interface at neutral and basic pH's and stabilize the Pickering emulsions, while in the acidic range, at pH ∼4, the emulsion separates into emulsion and serum phases due to flocculation. The observed process is reversible for at least five cycles. Optimal formulation of a Pickering emulsion composed of rosemary oil, an essential oil, and water has been achieved by ultrasonication and results in droplets of approximately 300 nm in diameter with an oil/water ratio of 0.11 (v/v) and 0.30-0.35% (wt %). Ionic stabilization is observed for concentrations up to 250 mM NaCl and pH values from 7 to 11. The emulsions are stable for at least 10 days when stored at different temperatures up to 50 °C. The resulting Pickering emulsions of different compositions also form a gel-like structure and show shear thinning behavior under shear stress at a higher oil/water ratio.