Characteristics of Oil-in-Water Emulsions Stabilized by Soy Protein and Lecithin Using Premix Microchannel Emulsification

Abstract

This study characterized oil-in-water (O/W) emulsions produced by premix microchannel emulsification (PMCE) using soybean-derived emulsifiers: soy protein isolate (SPI), modified lecithin (ML), and soy lecithin (SL). Mean droplet diameter (d₄,₃) and relative span factor (RSF) were evaluated under varying emulsifier concentrations, dispersed phase fractions, operating pressures, and pass numbers, whereas flux and storage stability were examined for selected representative systems. Among the hydrophilic emulsifier concentrations tested, only SPI significantly affected both d₄,₃ and RSF. Increasing SPI concentration from 0.2 to 0.6% increased d₄,₃ from 9.60 to 12.83 µm, while reducing RSF from 2.45 to 1.55, indicating the formation of larger but more uniform droplets. SL addition induced nonlinear responses in the SPI and ML systems. In the ML system, increasing the initial dispersed phase fraction in the premix from 5 to 25% increased d₄,₃ from 3.69 to 14.27 µm and decreased RSF from 8.43 to 2.31, suggesting a shift in breakup behavior. The d₄,₃ value increased with operating pressure in all systems, whereas a second pass did not significantly affect either d₄,₃ or RSF in any group. Owing to its interfacial activity, low interfacial tension (7.23 mN/m), and low bulk viscosity (1.54 mPa·s), 0.3% ML showed the highest flux, reaching 60.4–77.2% of that of Tween 80 at 5–15 kPa. Overall, 0.6% SPI provided the best balance of droplet uniformity and storage stability. These findings advance the mechanistic understanding of emulsion behavior under PMCE and guide the optimization of low-energy emulsification processes suitable for shear-sensitive or heat-labile formulations.