Effects of Transglutaminase Enzyme on the Structural Properties and Quality of Textured Soybean Protein Produced by High-moisture Extrusion

To investigate the influence of varying transglutaminase (TG) levels on the fibrous structure and quality of soy texturized protein, soy protein isolate was used as the main raw material, supplemented with 0% (control), 0.1%, and 0.3% TG. High-moisture extrusion was performed using a twin-screw extruder, followed by structural characterization of the resulting texturized proteins via texture analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy. Quality parameters such as color, expansion ratio, water-holding capacity, and oil-holding capacity were also evaluated. Compared with the control, TG-treated samples exhibited significantly (P<0.05) higher elasticity (0.92) and chewiness (2525.39 g), with the 0.3% TG group reaching the greatest hardness (3514.50 g). Increasing TG content significantly (P<0.05) enhanced the expansion ratio and darkened the color. Adding the appropriate amount of TG enzyme increased the water-holding capacity (by 0.1%) and oil-holding capacity (by 0.3%) of soybean histones. Scanning electron microscopy confirmed a more meat-like fibrous structure at 0.3% TG, and infrared spectroscopy revealed a shift from α-helices and β-turns toward β-sheet conformations, indicating bond breakage among protein molecules, unfolding of the native conformation, and subsequent denaturation and aggregation. This research provides a theoretical foundation for understanding texturized protein formation mechanisms and developing plant-based protein products.