Preparation of W1/O/W2 emulsions and droplet size distribution measurements by pulsed-field gradient nuclear magnetic resonance (PFG-NMR) technique

Multiple emulsions of W-1/O/W-2 type are of major interest in life sciences, offering possibilities for the encapsulation of water-soluble active agents. In food science, they are also applied for fat reduction. The droplet size distributions of the inner and outer emulsions are of main importance as they influence the theological and sensorial properties, the release kinetics, as well as the structural and microbial stability. However, the determination of the inner and outer droplet size distributions is a major challenge, as conventional measurement techniques cannot be applied. Pulsed-field gradient nuclear magnetic resonance (PFG-NMR) is well known as a non-destructive tool for droplet size determination, especially in simple emulsions. In this work, double emulsions of the W-1/O/W-2 type were prepared with polyglycerol-polyricinoleate (PGPR) and polyoxyethylen-20-sorbitan monolaurate (Tween 20) as emulsifiers by means of rotor-stator emulsification machines. PFG-NMR was applied for measurements of the inner phase (W-1) droplet size distribution as well as for the characterization of the O phase. The W-1 values were compared with results from laser light diffraction of simple emulsions (W-1/O type) and were found to be consistent within the experimental errors, if restricted diffusion in the outer water phase (W-2) and additional effects are considered.