Double emulsions: Potential applications for the elaboration of functional foods

Abstract

Double or water-in-oil-in-water (W1/O/W2) emulsions are complex systems consisting of an aqueous phase dispersed in a lipid phase, which in turn is dispersed in a continuous aqueous phase. Because these systems include water within the dispersed lipid phase, they have been proposed for the development of lipid-reduced food emulsions without the need of reducing the volume fraction of dispersed phase. The other potential application of W1/O/W2 emulsions is the encapsulation of substances in the inner water droplets for their isolation, protection or controlled release. The limits of these systems are given by the volume of water droplets that can be retained within the oil droplets and the minimum required size of oil droplets, which should be large enough to contain smaller water droplets. These conditions imply that W1/O/W2 emulsions present new issues regarding the stability of the system, adding different destabilization processes that should be controlled and measured. Different strategies have been implemented to increase the volume and stability of the inner water droplets, such as the generation of an osmotic gradient by the addition of solutes in the dispersed aqueous phase or the inclusion of fat crystals in the dispersed lipid phase. With respect to proper applications of W1/O/W2 emulsions for the production of functional foods, different objectives have been boarded: encapsulation of vitamins, minerals or microorganisms; formulation of low-calorie foods; control of taste perception; etc. Moreover, different methods have been developed for the analysis of W1/O/W2 emulsions, including spectrophotometry, conductimetry and differential scanning calorimetry techniques.