Biomass-based particles for the formulation of Pickering type emulsions in food and topical applications

Pickering emulsions are emulsions that are stabilized by fine particles. They have been the focus of considerable research in the past decade due to their properties such as high stability with respect to coalescence and Ostwald ripening, as well as due to advances in nanotechnology that allows us to create and characterize nano-scale structures in new ways. This work reviews some of the recent work in the area of biomass-based particles for Pickering emulsions in the context of foods and topical creams, and discusses some of the theory and particularities of Pickering type emulsions. Formulation examples are given with a focus on two types of biomass-based particles isolated with their natural structure intact: starch granules from quinoa and egg yolk granules. In contrast to particles commonly used for Pickering emulsions such as latex, silica, and clay particles, starch (including hydrophobically modified starch) and egg-fractions are accepted food ingredients, as well as pharmaceutical and cosmetic excipients. The particle stabilization of emulsion drops is possible due to partial dual wettability of particles at the oil–water interface. Native starch is not intrinsically hydrophobic; however hydrophobicity can be increased by chemical modification with octenyl succinic anhydride. Egg-granules on the other hand are quite hydrophobic and at low ionic strength (<0.3 M NaCl) are insoluble with a compact structure. Quinoa starch granules and egg-granules can be used to generate Pickering type emulsions in the 10–100 μm range with high levels of stability. Size decreased with increasing concentration and could be controlled by the granule to oil ratio. In the case of starch granule stabilized oil drops, heat can be applied to induce a partial gelatinization of the starch granules forming a cohesive layer at the oil–water interface increasing barrier properties. Although the droplet size of granule stabilized emulsions was relatively large, their excellent stability, encapsulation properties, and freeze–thaw stability can prove suitable for applications such as encapsulation of sensitive, bioactive ingredients in food and topical formulations.