Freeze-Induced Structuring of Soy Protein Isolate Gels: Characterization and Comparison with Meat Products

Population growth and the increasing demand for more sustainable foods have driven the development of alternative proteins for food applications. In this context, soy protein isolate (SPI) gels have attracted considerable attention due to their potential to reproduce the structural and textural attributes of meat products. This study evaluated the influence of solids content, pH, and freezing temperature on the structuring of SPI gels. The effects of these variables on hardness (Y₁) and cohesiveness (Y₂) were investigated using a full 2³ factorial design with duplicate center points. Hardness was influenced by all main effects, as well as by the interactions between solids content and pH and between solids content and freezing temperature. For cohesiveness, significant effects were observed for solids content, pH, and the interactions between solids content and pH and between pH and freezing temperature. The gels exhibited texture and color properties comparable to those of beef sirloin, chicken breast, and fish fillet, in addition to pH values ranging from 5.54 to 6.54, titratable acidity from 0.079 to 0.167 g lactic acid/100 g, water activity between 0.992 and 0.996, and moisture content ranging from 63.35% to 69.84%. Treatments S6 (13% solids, pH 5.0, and −5 °C), S8 (13% solids, pH 6.0, and −5 °C), and S9 (9% solids, pH 5.5, and −10 °C) exhibited lamellar structures and a texturization degree greater than 1, indicating structural alignment promoted by directional freezing, which was subsequently confirmed by the freezing curves. The results demonstrate that controlling the freezing conditions directly influences the structuring of SPI gels, enabling the production of materials with lamellar organization and textural properties similar to those of meat products. Among the conditions evaluated, 9% solids, pH 5.5, and −10 °C proved to be the most suitable for promoting SPI gel structuring.