Abstract
HypothesisIn the preparation of oleogels based on Pickering-emulsions, the choice of the preparation route is critical to withstand drying under ambient conditions, as it conditions the composition of the interfacial layer at the oil-water interface. ExperimentsHexadecane and olive oil oleogels were prepared using an emulsion-template approach from oil-in-water emulsions formulated with cellulose nanocrystals (CNC) and sodium caseinate (CAS) added in different orders (CNC/CAS together; first CAS then CNC; first CNC then CAS). The oleogels were formed from preconcentrated emulsions by drying at ambient temperature. The structure of the gels was characterised by confocal laser scanning microscopy, and the gels were assessed in terms of viscoelastic properties and redispersibility. FindingsThe properties of oleogels were controlled by 1) the composition of the surface layer at oil-water interface; 2) the amount and type of non-adsorbed stabilizer; and 3) the composition and viscosity of oils (hexadecane vs. olive oil). For the oleogels prepared from starting emulsions stabilized with CNC with subsequent addition of CAS, and free CAS present in aqueous phase, the elastic component was prevalent. Overall, the dominating species at the oil-water interface controlled the emulsion behaviour and stability, as well as viscoelastic behaviour of the resulting oleogels and their redispersibility.
Highlights
The development of structured liquid oil-based gels has attracted a great deal of interest from researchers looking for cross-linking agent-free ways to convert liquid oils into gel-like substances [1], often aiming at using liquid oil-based soft solids in drug delivery and food related applications
All distributions were multimodal, which applies to primary emulsions prepared with olive oil (OO) at both concentrations of stabilizers (0.2 and 0.3%)
The OO emulsions with CAS displayed a similar course of distributions and differed only in the droplet sizes, which depended on the CAS content
Summary
The development of structured liquid oil-based gels (oleogels) has attracted a great deal of interest from researchers looking for cross-linking agent-free ways to convert liquid oils into gel-like substances [1], often aiming at using liquid oil-based soft solids in drug delivery and food related applications. There are two main physical approaches for preparing oleogels It can be either a direct oleogelation using a structuring agent in the oil phase [2,3] or an indirect method employing emulsions as templates followed by water removal [1,4,5,6]. Et al (2015) studied oleogelation using a hydrophilic matrix of biopolymers Their method involved oil-in-water emulsion template stabilized by gelatin and xanthan gum [3] with water removal at high and low temperatures. The first step comprises formulating a surfactant-free oil-in-water emulsion stabilized by protein and cellulose nanoparticles, followed in the second step by removal of the water phase by centrifugation and evaporation This allows the formation of a matrix of watersoluble biopolymer and nanoparticles. The advantage of the reported system is the unique ability of CNC and CAS to form oleogels at low stabilizer concentrations and without additional thickeners
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