Essentials oils exist in liquid form at room temperature. Therefore the simplest form of encapsulation consists in emulsifying or dispersing the components in an aqueous so- lution. The main drawback of this formulation is the handle difficulty. This problem can be overcome by producing a dry formulation by microencapsulation, entrapping the oil drops in a carrier material.
Encapsulation techniques can be divided into three classes: chemical processes like molecular inclusion or inter- facial polymerization, physicochemical techniques like coac- ervation and liposome encapsulation and physical processes like spray drying, spray chilling/cooling, co-crystallization, extrusion or fluidized bed coating. The use of supercritical fluids as an alternative medium for formulating essential oils can improve the results obtained with other physical or phys- icochemical techniques, or even make possible innovative formulations, due to the peculiar properties of supercritical fluids in general and of supercritical carbon dioxide in par- ticular (adjustable solvent power, favourable transport prop- erties, no contamination of the product) which are signifi- cantly different from those of gas and liquid solvents [27]. The objective of this review is to provide an account of the principal technologies used for encapsulation of essentials oils, and to present innovative applications of supercritical fluids in this field.