The Impact of Homogenization Techniques and Conditions on Water-In-Oil Emulsions for Casein Hydrolysate–Loaded Double Emulsions: A Comparative Study

Abstract

This study aims to evaluate homogenization techniques and conditions for producing stable, small droplet-size water-in-oil (W/O) emulsions intended for incorporation into casein hydrolysate–loaded double emulsions. Three commonly used homogenization methods; rotor–stator, ultrasonic, and high-pressure homogenization were individually optimized utilizing response surface methodology. Instances of over-processing were observed, particularly with the rotor–stator and ultrasonic homogenizers under specific conditions. Nevertheless, optimal conditions were identified for each technique: 530 s at 17,800 rpm agitation speed for the rotor–stator homogenizer, 139 s at 39% amplitude for the ultrasonic homogenizer, and 520 s at 1475 bar for the high-pressure homogenizer. Subsequently, the W/O emulsions produced under optimal conditions and their respective W₁/O/W₂ double emulsions were compared. The rotor–stator and high-pressure homogenized W/O emulsions exhibited comparable narrow droplet-size distributions, as indicated by similar Span values. However, high-pressure homogenization failed to sufficiently minimize droplet size. Ultrasonic homogenization resulted in droplets at the 1-μm scale but yielded more polydisperse droplet-size distribution. According to TOPSIS analysis, an emulsion with a viscosity of 93.1 cP (centiPoise), a stability index of 93.8%, a D(90) of 0.67 μm (0th day), and a D(90) of 0.75 μm (30th day) produced using a rotor–stator was selected. Additionally, double emulsions containing primary emulsions prepared with the rotor–stator method demonstrated higher viscosity, narrower droplet-size distribution, and lower creaming compared to other samples. This investigation sheds light on the influence of homogenization techniques on emulsion properties, providing valuable insights for optimizing double emulsion formulations.