O/W emulsions stabilised by solid lipid particles: understanding how the particles’ Pickering functionality can be retained post their dehydration and subsequent rehydration

Pickering particles have been extensively shown to hold an immense potential as emulsion stabilisers. Lipid-based particles in particular, are increasingly studied as edible Pickering structures. The aim of this work was to investigate whether specific formulation parameters that are key for the fabrication of lipid particles with a Pickering functionality can also impact upon the ability of these structures to withstand drying and subsequent rehydration events, without loss to their original capacity to provide stable o/w emulsions. The formulation parameters studied here included the type of the lipid source, type and concentration of the surface active species and type and concentration of cryoprotectants used. Freeze-drying was used as the process for the dehydration of the fabricated lipid particles, while two methods for the subsequent rehydration of these structures were tested. It is demonstrated that lipid particles fabricated using sodium caseinate during the melt-emulsification step can maintain their original Pickering functionality even following lyophilisation; i.e., once reconstituted, they provide stable o/w emulsions with the same droplet sizes as those produced by their precursors (lipid particles that haven't undergone the freezing and desiccation stages). In contrast, a typical small molecular weight surfactant (Tween 80) does not exhibit the same functionality as the protein, and lipid particle agglomeration following drying and reconstitution was unavoidable, even in the presence of traditional drying aids (cryoprotectants) in the formulation. Parameters relating to the drying and rehydration stages (drying kinetics, final moisture content and storage conditions) were also studied, but their impact upon the Pickering functionality of the reconstituted lipid particles was deemed secondary to the effects brought upon by changes to formulation elements. 

Overall, the present work advances the current limited understanding on formulation approaches that enable the conservation of the Pickering functionality of the lipid particles following their drying and rehydration, in particular offering insight into the contribution of the specific emulsifier employed during particle fabrication.