Proteins, polysaccharides, and their complexes used as stabilizers for emulsions: alternatives to synthetic surfactants in the pharmaceutical field?

Emulsions are widely used in pharmaceutics for the encapsulation, solubilization, entrapment, and controlled delivery of active ingredients. In order to answer the increasing demand for clean label excipients, natural polymers can replace the potentially irritative synthetic surfactants used in emulsion formulation. Indeed, biopolymers are currently used in the food industry to stabilize emulsions, and they appear as promising candidates in the pharmaceutical field too. All proteins and some polysaccharides are able to adsorb at a globule surface, thus decreasing the interfacial tension and enhancing the interfacial elasticity. However, most polysaccharides stabilize emulsions simply by increasing the viscosity of the continuous phase. Proteins and polysaccharides may also be associated either through covalent bonding or electrostatic interactions. The combination of the properties of these biopolymers under appropriate conditions leads to increased emulsion stability. Alternative layers of oppositely charged biopolymers can also be formed around the globules to obtain multi-layered "membranes". These layers can provide electrostatic and steric stabilization thus improving thermal stability and resistance to external treatment. The novel biopolymer-stabilized emulsions have a great potential in the pharmaceutical field for encapsulation, controlled digestion, and targeted release although several challenging issues such as storage and bacteriological concerns still need to be addressed.