OBJECTIVES: Soybean dreg is a by-product of soy milk processing, which contains high levels of soluble dietary fibre (SDF). In this study, we aimed to provide comprehensive processes of pretreated extrusion for the improving structure and properties of soybean dreg soluble dietary fibre (SDSDF), which would be a valuable approach to enhance physiological activity. 

METHODS: Here, we characteristic the functional role of SDSDF employing to extrusion pretreatment. Soybean dregs were pre-treated using the twin screw extrusion method followed by enzymatic modification using neutral protease, α- amylase, glucoamylase, and cellulose to produce SDSDF. The physical properties and antioxidant activity of SDSDF were investigated. 

RESULTS: The morphology and crystal structure of SDSDF were observed that, through extrusion processing and enzymatic modification, the SDSDF yield increased by 106.28%. Moreover, the surface structure showed block-shaped or reticular formations in the extruded SDSDF, and the size of block-shaped cells was about 10 μm. Infrared spectroscopic analysis showed that a characteristic absorption peak of polysaccharide appeared at 1631 cm^-1 during extrusion processing. However, after extrusion processing, decreased absorption peaks were observed for the extruded SDSDF. Furthermore, XRD analysis showed that the 2θ diffraction peak changed at 24.16° for the extruded SDSDF. 

CONCLUSIONS: The overall findings suggest that the water holding capacity (WHC), oil holding capacity (OHC), expansibility, and the water solubility were signifcantly decreased in extruded SDSDF. In addition, the scavenging ability of 1,1-diphenyl-2-picrylhydrazyl (DPPH), -OH, O₂-, and the total reducing power were significantly improved, indicating that beneficial changes had taken place in the crystal structure of cellulose or hemicellulose to improve the physiological activity in extruded SDSDF.