A successful design of nanoemulsions involves the use of the appropriate emulsifier(s) that will act on the surface of the dispersed phase, been adsorbed on it, leading to further droplet disruption and hindering droplet recoalescence or aggregation (Ziani, Fang, & McClements, 2012).
There are several emulsifiers been exploited in the food industry, categorized as small molecule surfactants, phospholipids, proteins [e.g., casein, (3-lactoglobulin (|3-lg)] or even polysaccharides (e.g., carboxymethyl cellulose) (Assadpour, Jafari, & Maghsoudlou, 2017). Food-grade emulsifiers such as polysaccharides are recently used in the food industry including hydrocolloids or modified starches. Emulsifiers have a specific interfacial behavior; they decrease the interfacial tension of the oil and water phases, but could balance electrostatic forces or result in steric repulsion, rheology change, and increased loading capability (Anton, Benoit, & Saulnier, 2008; Hategekimana, Masamba, Ma, & Zhong, 2015). When formulating nanoemulsions, the surfactant (emulsifier) concentration is quite important. As the particle surface increases, a greater amount of emulsifier is required to completely cover the oil droplets avoiding any destabilization.
Concerning the small molecule surfactants used in nanoemulsion formulation, there is a great variety of choices. Some examples of nonionic surfactants are sorbitan esters (e.g., span and tween series, mostly 40, 60, or 80), polyoxyethylene ethers (e.g., Brij), monoglycerides, sugar esters, and polyglycerol esters of monolaurate (Rao & McClements, 2012). Small molecule surfactants can form easily small droplets, compared to biopolymers. Due to their large molecules, protein- or polysaccharide-based emulsifiers, adsorbed at the interfacial layer, lead to a significant droplet size increase.
Substances with thickening or gelling properties act as stabilizers. In emulsions, they are added into the aqueous phase and due to a viscosity increase, oil droplets movement is then retarded. However, modifying the aqueous phase rheology, changes also the mouth feel and texture (e.g., creaminess, gel strength) and new structures are created (Tang, Sivakumar, & Nashiru, 2013). Most stabilizers used in emulsions are hydrocolloids such as gum Arabic, pectins, xanthan, modified starch, alginates, galactomannans, and chitosan.