Three-dimensional porous fibrous structural morphology changes of high-moisture extruded soy protein under the effect of moisture content

Water plays a key role for regulating the textural properties of protein fibrous and porous structure formed during the high-moisture (above 40%) extrusion process, which would further affect the taste of plant-based meat substitutes. In this study, soy protein concentrate (SPC) was selected to prepare the protein porous fibrous structure through high-moisture extrusion with the moisture content ranging from 50% to 70%, by evaluating the response of temperature, pressure, and specific mechanical energy (SME) simultaneously. The three-dimensional structural morphology features of the extrudates were systematically characterized and compared considering the color, texture, density, macro- and micro-structure and interaction with water. Results showed porous structure with different scales existed in all extrudates under varied moisture content. Obviously, the hardness, chewability, shear force, tensile resistant force and tensile distance gradually decreased with the increase of moisture content. It was found that the higher the moisture content, the worse the protein molecular orientation along the extrusion direction, resulting in a less-texturized uniform structure. Moreover, under the higher moisture content, the protein skeleton in the extrudate was thinner with larger pores. Water characteristics analysis showed that increasing the moisture content could disrupt the binding between protein structure and water, which was not conducive to water retention and more water dispersed around the surface of cross-linked protein structure. This study would be helpful for the design of protein porous fibrous structure through high-moisture extrusion toward the plant-based meat substitute development.