Modulation of Rheological Properties and Liquid-Holding Capacity in Soy Protein Isolate Oleogels Based on Capillary Bridging Effect

In this study, a soybean protein isolate (SPI) oleogel system was established based on capillary bridging effect. The influence of the secondary fluid addition, particle concentration, and heat treatment temperature on the gelation properties of the resultant oleogels was explored. The visual appearance, liquid-holding capacity, and rheological properties were investigated. Results showed that, in the SPI-soybean oil suspension with ratio of 3:7 (w/w), when the secondary fluid addition amount reached approximately 25% (w/w), the system underwent a sol-gel transition, shifting from a viscous flowing fluid to a semi-solid state with self-supporting ability. When the secondary fluid addition amount was higher than 50%, the liquid-holding capacity rose to over 60%. As the SPI particle concentration increased, the proportion of particles in the system increased accordingly, resulting in formation of a tighter protein network structure that was more effective at immobilizing the liquid oil. Once the particle concentration surpassed 35%, the liquid-holding capacity climbed to above 75%. Further investigation indicated that heat treatment was an effective post-treatment approach. Specifically, when the heat treatment temperature increased from room temperature to 90 ℃, the liquid-holding rate increased by 11.85% (compared with control group), and the storage modulus increased to 1.43×10⁵ Pa. The FTIR results indicated that heat treatment caused changes in the secondary structure of SPI molecules within the system, with an increase in the β-turns and random coil structures. This suggested that the enhanced gelation properties of the oleogel might be due to the dynamic alteration of the interfacial properties of the protein particles, leading to enhanced hydrophobic interactions in the system and the formation of a more robust gel structure. This work established a theoretical basis for development and property regulation of soybean protein-based fat alternatives and provided guidance for healthy food design.