Crystallizable W/O/W double emulsions made with milk fat: Formulation, stability and release properties.

Food grade Water-in-oil-in-water W/O/W double emulsions with high encapsulation efficiency, controlled texture and triggered leakage are usually sought after in many food applications (e.g. functional foods) and still the subject of active research interest. For that purpose, we have used an edible crystallizable oil which is Anhydrous Milkfat (AMF) with high encapsulation properties, as recently demonstrated. The emulsions encapsulating a nutrient (MgCl2) were formulated using two surface-active species (polyglycerol polyricinoleate and sodium caseinate being also a chelating agent able to bind magnesium ions). The internal droplet and oil globule diameters were identical for all the systems. The stability of the double emulsions and the rate of magnesium release from the internal to the external aqueous phase were monitored during 24 days of storage at 4 °C, as a function of the formulation and globule volume fraction. It was found that in all cases, magnesium leakage occurred without film rupturing (no coalescence) and the double structure was preserved with time. On the other hand and at iso-osmotic conditions, the rate of Mg release was low (does not exceed 14% after 24 days of storage at 4 °C), independent on the concentration of sodium caseinate in the external aqueous phase, remained time independent and its level of release was lowered by increasing the globule volume fraction. Under moderate hypo osmotic conditions (∆P = +1.159 atm until +3.343 atm), the Mg release increased with the osmotic pressure gradient but remained also time independent. However, at large osmotic gradient (∆P = +5.503 atm), the Mg2+ release was triggered fastly and increased with time, in agreement with a no more protective structure, being beneficial for several food applications. The experimental data were interpreted and the permeation coefficient of Mg was determined within the frame of a mean-field model based on diffusion/permeation, integrating the transport in opposite direction than Mg2+, of the osmotic regulator, even occurring at different rates through the oil phase. Under hyper osmotic conditions (even large, ∆P = -7.502 atm), the Mg release was low, time independent and the double structure was usually preserved over time. So, this study allows to improve magnesium retention and its controlled release, in particular for nutritional and food applications.