Water binding ability changes of different proteins during high-moisture extrusion

High-moisture extrusion technology (40% similar to 80% moisture content) has shown the advantages for producing plant-based meat products with rich meat-like fibrous structures; however, it faces the issue of insufficient juiciness. Juiciness is associated with water characteristics such as water holding capacity and water distribution, and the variations in water binding ability of proteins during high-moisture extrusion may offer valuable insights into this perspective. Thus, the water binding ability changes of plant proteins from five common sources during high-moisture extrusion were investigated in this study. Results showed the extrudates of soy protein isolate (SPI), soy protein concentrate (SPC) and wheat gluten (WG) exhibited fibrous structures at a centimeter level, respectively, and the microscopic morphology of SPI extrudates was more uniform. SPI showed the strongest water holding capacity and highest gel strength, leading to a faster binding rate with water compared to other proteins during the heating process. Moreover, the lowest water activity, freezable water content, T-21 and T-22 were found after extrusion of SPI, indicating that it was the most tightly bound to water. While, rice protein isolate (RPI) failed to extrude into a regular shape, and its extrudates showed the lowest density with a poor water binding ability. It was also found that the water activity of the extrudates was related to the solubility of the protein raw materials, and proteins with high solubility (PPP) showed lower water activity after extrusion. The results confirmed that the water binding ability of proteins could affect the water content, water state and distribution in the extrudates. These findings provided evidence for exploring the juiciness of plant-based meat products from the perspective of protein-water interaction.