O/W Pickering emulsions stabilized by cocoa powder: Role of the emulsification process and of composition parameters

We fabricated oil-in-water emulsions stabilized by delipidated commercial cocoa powder. The emulsions were characterized in terms of droplets and particles size distribution and interfacial coverage by cocoa powder by developing methods to separate droplets from adsorbed and unadsorbed cocoa particles. Three different processes were compared for their ability to produce fine and stable emulsions: rotor/stator turbulent mixing, sonication and microfluidization. Among those techniques, microfluidization was the most performing one. In this case, micron-sized emulsions with narrow size distributions could be obtained with >90 wt% of the powder insoluble material anchored to the interfaces, and they were still stable after 90 days. It was demonstrated that the mixing process did not generate finer cocoa particles but provoked disentanglement of the large primary particles, providing them an open, expanded structure that facilitated emulsification. It was also shown that the finer insoluble fraction of the powder and the soluble fraction had no significant impact on emulsification and on kinetic stability. In the poor particles regime, the oil-water interfacial area varied linearly with the amount of adsorbed powder, suggesting that the final droplet size was controlled by the so-called limited coalescence process, as already observed in conventional Pickering emulsions stabilized by spherical solid particles.