Temperature-Mediated Structure–Functionality Changes in Soybean Meal Protein via Extrusion

Soybean meal protein, a byproduct of soybean processing, has limited functional properties such as emulsifying performance, which restricts its application in foods. Given that high-temperature extrusion tends to cause excessive denaturation and irreversible aggregation, this study aimed to investigate the effects of relatively low extrusion temperatures (85-105 °C) on the structural and functional properties of soybean meal protein. The results showed that extrusion altered the molecular structure and functional characteristics of the protein. With increasing extrusion temperature, the β-sheet content increased while the α-helix content decreased in the secondary structure, and tertiary structural rearrangements occurred, with hydrophobic groups being exposed and subsequently buried. At 95 °C, the protein formed a relatively porous and loose microstructure and exhibited the strongest surface hydrophobicity, water-holding capacity, oil-holding capacity, and emulsifying properties; at 100 °C and above, excessive aggregation occurred, pore structure collapsed, and functional properties declined. Meanwhile, extrusion generally reduced protein solubility. Therefore, 95 °C is identified as the optimal extrusion temperature under the conditions of this study. In addition, this study reveals the correlation between structural reconstruction and functional changes of soybean meal protein, providing a theoretical basis for its high-value utilization and application in the food industry.