Preparation and Stability of Soy Protein Isolate-Xanthan Gum Composite and Bilayer Emulsions

To enhance the stability of emulsions prepared with soybean protein isolate (SPI) as the sole emulsifier, this study developed composite sunflower seed oil emulsions (SPI-XG-e) and bilayer emulsions (SPI-e/XG) using SPI and xanthan gum (XG) as co-emulsifiers. The primary objective was to investigate the effects of XG concentration on the physical characteristics of the emulsions, including mean particle size, zeta potential, and turbidity, as well as their overall stability. The findings revealed that at a XG concentration of 1.0%, the bilayer emulsion demonstrated superior physical properties, characterized by a more uniform particle size distribution, a smaller mean particle diameter (0.63±0.03 μm), a higher absolute Zeta-potential value (46.70±0.25 mV), and a lower centrifugal stability constant (0.70%±0.46%). Comparative analysis of the composite and bilayer emulsions revealed that the latter exhibited enhanced environmental stress tolerance. Particularly, the bilayer emulsion prepared with 1.0% XG could maintain homogeneity for 7 days of storage at 4 °C with no detectable phase separation. After thermal treatment at 90 °C, it retained a high absolute Zeta-potential value (44.47±0.31 mV) and showed no flocculation following three freeze-thaw cycles, demonstrating robust stability. This study provides actionable guidelines for developing highly stable oil-in-water emulsions in food manufacturing processes.