Impact of the encapsulated salt characteristics on its release from multiple W/O/W emulsions

Abstract

AbstractW/O/W emulsions based on Miglyol oil and stabilized by polyglycerol polyricinoleate and sodium caseinate were prepared with similar characteristics in terms of internal droplet diameter, oil globule diameter, internal aqueous fraction and fat globules fraction. The emulsions differ only by the nature of the encapsulated salt in the inner aqueous droplets. The release of each encapsulated salt from the internal to the external aqueous phase was followed during 30 days at 25°C, showing for all cases that the double structure was preserved with time and the release increased during storage, mainly according to diffusion/permeation mechanism and resulting in a competition between the chelation and the hydration enthalpy of the salt. Double emulsions encapsulating different Magnesium salts have shown that the release depends strongly on the anion via its magnesium chelation and its hydration enthalpy. Indeed, as the complexation constant of Mg2+ with its counterion increases, the leakage decreases. On the other hand, as the hydration enthalpy of Mg2+ counterion decreases, the leakage decreases too. Likewise, double emulsions encapsulating different chloride salts have shown that the release depends also on the cation via its hydration enthalpy and its chelation with caseinate affecting accordingly the stiffening of the globule/water interface, more pronounced for bivalent than for monovalent cations. It was thus directly highlighted that the release from W/O/W emulsions was well controlled by the characteristics of the salt, and anion and cation diffuse accompanied at a rate ensuring the electroneutrality of the diffusive species. These results are very useful not only in term of fundamental understanding but also on application level, especially for food supplementation such as of dairy product.Practical applicationsThe search for an innovative functional effect can lead to food supplementation with bioactive substances which can be either molecules or living bioactive cells. However, the direct addition of these substances to food can induce chemical degradation, aggregation of proteins and generate an unpleasant taste. These drawbacks can be avoided or at least reduced by encapsulation. Despite their thermodynamic instability, W/O/W emulsions are promising systems for encapsulation of hydrophilic species in their internal aqueous phase and hence find applications among others in food for taste masking or supplementation. The release of the encapsulated species to the external aqueous phase should be controlled, depending on the desired application. The release depends also on the characteristics of the encapsulated salt. A better understanding of its impact on the stability of the double emulsion will allow targeting formulation of stable emulsions and hence contributing to their better industrial development.