Automated image analysis as a control tool for multiple emulsions

The industrial preparation of multiple emulsions of the W1/O/W2 type requires process control of the W1-yield. The aim of this study was to develop automated image analysis of W1/O/W2 emulsions for visualizing oil droplet size as well as the distribution of the inner aqueous W1-phase. In order to obtain different emulsion properties, i.e. an external oil droplet size 5–50 μm, the process parameters of the second emulsification step using of microporous membranes were varied. The emulsions were characterized by particle size distribution measured by laser diffraction, microscopy and image processing, and release rate of a model substance (Poly R-478). Membrane emulsification resulted in multiple emulsions with a yield of the W1-phase close to 100% and a tailored particle size range. Proteins were suitable emulsifiers to create coalescence-stable multiple emulsions at low energy input. Measuring the size distribution of the oil droplets by laser diffraction confirmed the results obtained by automated image processing. Due to an internal droplet size <1.5 μm the W1-droplets were not visible as discrete particles but as texture at 400× magnification. The evaluation of several statistical data extracted from the intensity level within the oil droplets showed that the relative brightness was particularly suitable to control the filling level of the oil droplets with W1.