Differential scanning calorimetry (DSC) in multiple W/O/W emulsions: A method to characterize the stability of inner droplets

Multiple water-in-oil-in-water (W/O/W) emulsions offer a huge potential as encapsulation systems in different food, cosmetic, and pharmaceutical applications. Because of their complex structure, however, it is difficult to characterize these systems. Typical measurement techniques to determine the size and stability of the inner water droplets encapsulated in the oil droplets show limitations and inaccuracies. Determining the total amount of water in the inner droplets is most often done by indirect methods to date. We describe an analytical method based on differential scanning calorimetry (DSC) for characterizing the total amount of encapsulated water droplets and their stability in W/O/W multiple emulsions. It uses the possibility to directly determine the latent heat of freezing of water droplets of the same size and composition as in the multiple emulsions. The amount of water in the inner droplets of a W/O/W emulsion can thus be calculated very accurately. It is shown that this method enables furthermore detecting multi-modalities in the size distribution of inner water droplets in W/O/W emulsions. Changes in droplet size distribution of the inner droplets occurring during the second emulsification step of processing or during storage can be detected. DSC thus offers a powerful tool to characterize the structure of multiple W/O/W emulsions.