Microfluidic technique as a tool for producing High Internal Phase Emulsions (HIPEs)

High internal phase emulsions, aka HIPEs, have gained significant interest due to their exceptional rheological properties, stability, and versatile industrial applications. Specifically, water-in-oil (W/O) HIPEs offer great potential as a low-calorie alternative to be applied as fat replacers in food products, in addition to be an efficient vehicle for active compounds. Nonetheless, conventional production processes that employ high-intensity mechanical energy often yield highly polydisperse water droplets. Microfluidics then emerges as an attractive solution, enabling the controlled formation of uniform and monodisperse droplets that can promote a suitable encapsulation of components. In face of this, this study aims to understand the effect of process conditions, such as different pumping pressures and microchannels design (T-junction and flow-focusing), on the production of W/O HIPEs in microfluidic chips. The role of polyglycerol polyricinoleate (PGPR) in stabilizing the W/O interface was also investigated. For this, sunflower oil with 1.5% (w/w) PGPR served as the continuous phase (CP), while deionized water acted as the dispersed phase (DP). The microdevices were produced using soft lithography and PDMS as the building material. W/O HIPEs generated within the devices were characterized according to droplet size distribution, microstructure and moisture content. W/O HIPEs could be produced only in flow-focusing chips, as confirmed by microscopy. Moisture content was 78.1 ± 1.2%. Under the best flow-focusing conditions, W/O HIPEs emulsions were produced employing a pumping ratio of 300 mbar (DP) and 400 mbar (CP). In chips' diameters of 3000 µm and 1000 µm, droplets were formed with a diameter of 7.20 ± 0.85 µm, Reynolds (Re) of 1.19.10-3 and 8.73 ± 0.85 µm, Re of 1.66.10-3, respectively. Thus, it is concluded that microfluidic devices can be used to form W/O HIPEs, but the process conditions have to be carefully selected to improve the droplets productivity.