Differential scanning calorimetry (DSC) in multiple W/O/W emulsions
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Differential scanning calorimetry (DSC) in multiple W/O/W emulsions A method to characterize the stability of inner droplets A. Schuch • K. Ko¨hler • H. P. Schuchmann
Received: 25 July 2012 / Accepted: 5 October 2012 / Published online: 9 November 2012 Ó Akade´miai Kiado´, Budapest, Hungary 2012
Abstract 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. Keywords Multiple emulsion Measurement Encapsulation efficiency Differential scanning calorimetry (DSC) Droplet size distribution
A. Schuch (&) K. Ko¨hler H. P. Schuchmann Institute of Process Engineering in Life Sciences; Section I: Food Process Engineering, Karlsruhe Institute of Technology, Haid-und-Neu Straße 9, 76131 Karlsruhe, Germany e-mail: [email protected]
Introduction Multiple water-in-oil-in-water (W/O/W) emulsions are complex multiphase systems that consist of a water-in-oil (W/O) emulsion dispersed in a second continuous water phase. They are also called emulsions of emulsions. There is a great interest in the production of multiple W/O/W emulsions for different applications ranging from separation technology [1], encapsulation of sensitive molecules for food [2, 3], cosmetic and pharmaceutical products [4–6] to fat reduction in food [7]. Because of the huge interfacial area caused by the complexity of these systems, they are in general thermodynamically highly unstable. Different mechanisms can cause destabilization during processing and storage [8]. The oil droplets as well as the inner water droplets may coalesce. Water as well as other ingredients can diffuse between the two water phases [9, 10]. In order to get control of these instabilities, it is necessary to detect and characterize droplet size distributions of inner and outer droplets
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