Particles in stabilizing food emulsions: a literature review
Emulsions are practically important to, and widely used in, food science and agricultural products fields. Investigations about food emulsion into the stability, interaction and structural relationships. (Tambe et al., 1993, Lissant, 1974) Food systems commonly contain particulate material that accumulates at oil–water, water-oil and air–water interfaces and contributes to the colloidal stabilization of emulsions. (Dickinson, 2006)After emulsification, sizes of particles in systems structure could vary widely from nanometers to micrometers, As emulsion droplets coated by a layer of adsorbed solid particles at the oil and water interface stabilizes the dispersed system, the mechanism is commonly referred to as Pickering stabilization. Oil- in-water (O/W) or water-in-oil (W/O) emulsions can be produced depending on whether the particles are predominantly hydrophilic or hydrophobic. Emulsifiers preferentially adsorb to the air/oil–water interface. This reduces the free energy involved with a high surface area interface, and as a result, reduces the interfacial surface tension (Nielloud and Marti, 2000) . Examples Pickering type of food emulsions are homogenized and reconstituted milks (O/W emulsions stabilized by casein micelles) and margarines and fatty spreads (W/O emulsions stabilized by triglyceride crystals) (Dickinson, 2006).
There have been a number of different particle types used as stabilizers in both O/W and W/O emulsions, Inorganic particles (especially silica nanoparticles), fat crystals, and protein-based nanoparticles. The effectiveness of a specific particle type in stabilizing an emulsion, depends on the emulsion medium, the particle shape and size, particle wettability and inter-particle interactions(Aveyard et al., 2003).
To help stabilize emulsions of pure components, it is normally necessary to add an additional component, the emulsifying agent. Emulsifiers are classically molecular surfactants (e.g. fatty acids or alcohols)(Weaire and Hutzler, 1999), polymers or larger protein type agents (e.g. egg albumen)(Shaw, 1966) . Polymers and proteins cause stability largely through electric and steric repulsion, controlled by the extent of unfolding and conformational layer structure on droplets(Dimitrova et al. 2004, Russey et al, 2004). Particles impart stability on emulsions primarily through a steric barrier, created at the interface. With a certain concentration of particles, a close packed network is generally formed, which further increases stability. It is also thought that a certain level of particle flocculation is advantageous for stability (Simovi and Prestidge, 2003).
Many naturally occurring emulsions will contain a variety of types of agents, leading to potentially very complex interactions giving overall characteristics. However, unlike emulsifiers, particles do not affect emulsion stability by significantly reducing the oil–water surface...