Cold-Set Gelation of Commercial Soy Protein Isolate: Effects of the Incorporation of Locust Bean Gum and Solid Lipid Microparticles on the Properties of Gels

This study aimed to evaluate the ability of commercial soy protein isolate (SPI) to form cold-set gels under different pHs (5–11), pre-heating temperatures (60 °C, 80 °C), CaCl₂ (0–15 mM) and SPI (5–15%, w/v) concentrations, and also select a formulation for the investigation of the effects of incorporating locust bean gum (LBG) (0–0.3%, w/v) and solid lipid microparticles (SLM) on gels rheological and microstructural properties. Gels were evaluated in terms of visual aspect, water-holding capacity, microstructure (using confocal laser scanning microscopy and cryo-scanning electronic microscopy) and rheological properties. SPI showed higher solubilities at pHs 7 (32.0%), 9 (51.6%) and 11 (100%). Self-supported gels were obtained under several conditions at alkaline pHs. At pH 7, only systems pre-heated to 80 °C with 15% (w/v) SPI and 10 or 15 mM CaCl₂ gave self-supported gels. At neutral pH, samples showed relative structural instability, which was minimized with LBG incorporation. Formulations G_SPI (pH 7, preheated to 80 °C, 15% (w/v) SPI, 10 mM CaCl₂) and G_MIX (pH 7, preheated to 80 °C, 15% (w/v) SPI, 0.2% (w/v) LBG, 15 mM CaCl₂) were selected for emulsion-filled gels (EFG) production. Power law parameters (K′, K″), calculated from frequency sweep results, revealed that non-filled G_MIX (K′: 472.1; K″: 77.6) was stronger than G_SPI (K′: 170.4; K″: 33.6). Besides, G_MIX showed microphase separation. SLM stabilized with Tween 80-Span 80 were active fillers in EFG, altering microstructures and increasing G’, G” and the Young’s modulus (1.8 to 2.1 kPa for G_SPI and 1.4 to 2.2 kPa for G_MIX).