Emulsion gels: The structuring of soft solids with protein-stabilized oil droplets

Many food products can be categorized as emulsion gels. This is especially the case for protein-based oil-in-water emulsions which can be converted into soft-solid-like materials by common food processing operations such as heating, acidification, and enzyme action. This review article outlines how the rheological and structural properties of protein-stabilized emulsion gels are influenced by the dispersed oil volume fraction, the oil–water interfacial composition, and the colloidal interactions of the constituent emulsion droplets. For model systems of variable oil content and containing different food proteins, some general trends of rheological behaviour at small and large deformations are identified. Experimental rigidity data are considered in relation to: (i) material science theories of the reinforcement of solid materials by active and inactive filler particles, and (ii) Brownian dynamics simulations of aggregated particle networks containing bonded and non-bonded particles. Influences of interfacial composition and particle–matrix interactions on microstructure and rheology are explained with particular reference to the role of small-molecule surfactants. Compositional and structural factors affecting the large-deformation rheology and fracture properties are described. Finally, the practical relevance of the model system studies to the behaviour of real food products is critically assessed.

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► Food emulsions gels are mainly formed by heating, acidification and enzyme action.
► Rheology and fracture properties depend on character of particle–matrix interactions.
► Protein-coated droplets are active fillers; surfactant-coated droplets are inactive fillers.
► Models of particle-filled gels and aggregated particle gels provide mechanistic insight.