Effect of high-moisture extrusion process on quality attribute and fibrous formation mechanism of pea protein: Insight into dynamic changes of textural protein

The high-moisture texturing extrusion process of pea protein isolate under different moisture contents (60 to 65%), barrel temperatures (110 to 150 °C) and screw speeds (85 to 115 rpm) has been investigated and optimized based on the water holding capacity, color changes, fibrous degree, chewiness and hardness. The result showed that moisture content significantly increased water holding capacity, decreased the possibility of the Maillard reaction and the fibrous degree, due to the decreasing viscosity of the molten protein caused by excess water. The sufficiently denatured protein extrudate with well-defined fiber formations can be obtained at higher temperature, which increased the anisotropy index of extrudate, and led to a significantly deeper color. The results from different zones of the extruders showed that the extrusion process promoted the spherical structure of the protein unfolding, and exposed more SH on the surface of the lamellar structure of the protein. The largest α-helix/β-sheet ratio can be obtained on extrudate, illustrated the formation of dense, rigid protein aggregates. The denaturation temperature of protein decreased from 73.55 to 64.18 °C under the action of shear stress, pressure drop and water evaporation of the extrusion die, which promoted the crosslinking between protein molecules. Moreover, the rigid extrudate with interlaced structures developed as a result of increased protein refolding and re-aggregation, enhancement of the degree of protein disorder, and promotion of the SH into SS bond transformation in cooling dies. The analysis of the tertiary structure also showed λmax steadily decreased as the fluorescence intensity increased during the cooling process. Overall, the appropriate extrusion parameters can improve the physical properties and quality attributes of meat analogues.