Water-in-oil-in-water double emulsions for food applications: yield analysis and rheological properties

Abstract

Water-in-oil-in-water (W/O/W) emulsions are systems in which a water-in-oil (W/O) emulsion is dispersed in a second aqueous phase. The W/O emulsion exists in the suspending aqueous medium as oil globules containing smaller water droplets. In this work the techniques of preparation and yield analysis of W/O/W emulsions are described; microstructure and rheological behavior are also studied with a view to possible food applications. In order to prepare W/O/W emulsions, a two-step emulsification technique was used. During the first step, a W/O emulsion was prepared in the presence of a lipophilic emulsifier while, during the second step, the W/O emulsion was mixed with an aqueous solution of a hydrophilic emulsifier to provide the W/O/W system. The yield of W/O/W emulsion was evaluated by measuring the amount of an ionic marker (NaCl) which migrated from the dispersed globules to the continuous aqueous phase, using dialysis to separate the NaCl migrated from the aqueous medium and using ionic chromatography to detect the amount of the NaCl outcome. The microstructure was investigated by making phase-contrast microscope photographs and estimating the size distribution of the oil globules. Finally, the rheological behaviour of W/O/W systems was studied by means of both steady-shear and oscillatory measurements.