Fate of edible solid lipid nanoparticles (SLN) in surfactant stabilized o/w emulsions. Part 2: Release and partitioning behavior of lipophilic probes from SLN into different phases of o/w emulsions

The release and partitioning of encapsulated compounds from solid lipid nanoparticles (SLN) to other matrix constituents was investigated in o/w emulsions stabilized by different surfactants (CTAB, SDS, Tween 20) by confocal laser scanning microscopy (CLSM) and electron paramagnetic resonance spectroscopy (EPR) spectroscopy. CLSM images revealed that the encapsulated probe Coumarin 6 (C6) was located in the oil droplets after SLN were mixed with the different emulsions. The EPR spin probe TEMPOL-benzoate (TB) showed different dynamics as a function of its specific solubilization sites in SLN. Four different populations of the spin probe could be separated giving the smallest population in the aqueous environment and the major population at the SLN interface. Two further populations were associated with differently crystalized lipid environments. This implies that both loosely structured regions with a-and beta'-polymorphs and environments of beta-polymorphs are present in SLN. In separated model emulsion systems, a prolonged release of TB from SLN was evident which predominately originated from the SLN interface. The released TB partitioned into the oil phase (25%) and into the o/w interface (30-45%), regardless of the presence or absence of additional surfactant micelles. Hence, these edible SLN may be used as delivery system for bioactive compounds in food emulsions with low impact of the surfactant used to stabilize the emulsion. The partial redistribution of the encapsulated compounds should be taken into account, but can also offer benefits when a prolonged release of lipophilic additives is desired.