Research on the Effects of Extruded Okara on Improving Gluten Protein Stability and Dough Processing Properties

Okara is a byproduct produced after grinding soybeans, but its poor taste and difficulty in storage have posed a severe challenge in handling it. This study aims to modify okara using single-screw extrusion technology to alter the ratio of soluble dietary fiber (SDF) to insoluble dietary fiber (IDF) and to investigate their effects on the protein conformation, rheological properties, and microstructure of wheat dough. The experimental results indicate that the SDF content in extruded okara was significantly increased by approximately 6.39%, with the swelling ability and hydration capacity increasing by 1.69 (g/g) and 2.4 (g/mL), respectively. The addition of 6%-9% extruded okara into the dough caused a redistribution of water, increased the proportion of bound water, altered the protein conformation, and increased the content of the α-helix structure. At the 9% addition level, compared to the control group, the content of α-helix increased by 4.45%, leading to the conversion of β-turns to β-sheets and forming a more stable gluten network structure. However, compared to untreated raw okara, adding extruded okara increased the dough's elastic modulus and loss modulus, lowered the tanδ value, reduced the pasting viscosity, and improved the viscoelastic properties of the dough. These findings deepen our understanding of the mechanism by which extruded, modified okara added to wheat dough affects its properties and provide theoretical guidance for applying extrusion modification technology in okara processing and the development of bakery products.