High moisture extrusion of soybean-wheat co-precipitation protein: Mechanism of fibrosis based on different extrusion energy regulation

The soybean-wheat co-precipitation protein (SWCP) is a composite protein that possesses a shared internal structure and a high nutritional value derived from the combination of soybean and wheat. However, the process of fibrosis formation during high moisture extrusion utilizing SWCP as a raw material for plant-based meat analogs has not been thoroughly well investigated. This study aims to examine the relationship between the formation of protein fiber and its molecular structure under varying extrusion parameters by extruding SWCP, blend protein (BP), soy protein isolate (SPI), and wheat protein (WP) with high moisture extrusion. Under identical extrusion conditions, SWCP extrudates exhibited greater fibrous structures, a higher total color variation index, and a lower browning index than BP extrudates. The textural properties of SWCP extrudates were significantly enhanced with increasing screw speed and temperature, with a maximum value of 1.91 N/N. Extrudates with higher moisture content resulted in decreased hardness, tensile strength, and chewiness. The extrusion process led to the formation of porous structures within the protein fibers, with water molecules primarily existing as immobilized water within the network structure (immobilized water content was 77.15%–92.84%). Compared to SWCP extrudates, water in BP extrudates was more prone to migrate. The structural analysis of the protein showed that during the extrusion process, the α-helix and β-sheet changed to β-turn and random coil structure. Hydrogen bonds, hydrophobic interactions, and disulfide bonds played a marginally more important role in stabilizing the protein structure of SWCP and BP extrudates. In conclusion, our research results showed that co-precipitation protein can have a positive impact on the quality characteristics of extrudates, and extrusion parameters have a significant effect on the formation of the fibrous structure of extrudates.