Changes of fibrous structure of high-moisture extruded pea protein isolate for three cooling die geometries

• Three cooling dies with varied sizes were designed for the high-moisture extrusion of pea protein isolate. • The mechanical energy of the flat die was sufficient due to its higher pressure response and convective heat transfer. • Texturization behavior of pea protein isolate was weakened from edge to center in the flat die. • Distribution of moisture in the extrudates was significantly affected by the wall area of the die. High-moisture extrusion has emerged as a promising technology for producing plant-based meat products with meat-like fibrous structure, wherein the cooling die is a key component. This study investigated the impact of three die dimensions (circular, square, and flat) on system response parameters, protein conformation changes, and the textural quality of pea protein isolate (PPI) extrudates. Results showed that the flat die with larger outlet dimensions, demonstrated reduced specific mechanical energy (669.99 kJ·kg -1 ) due to higher die pressure (4.34 MPa) and mass flow rate (299.40 g·min -1 ). Extrudates from the flat die exhibited a slender, tightly arranged fibrous structure, with enhanced mechanical properties and a maximum tensile resistant force of 0.30 kg. Moisture distribution (including bound and non-flowing water) was also significantly affected by the die wall. For the protein structural changes, the α-helix content in circular and square die extrudates was lower than that in flat die extrudates, with significant variations in secondary structure observed between the center and edge regions. However, no significant changes were found for the protein molecular weight. These findings highlight the importance of die wall area and distance from the wall in controlling extrudate quality, particularly in texture adjustments. This study provides a reference for optimizing fibrous structures by designing the die dimension. Graphical abstract: Effect of die design on the fibrous structure of high-moisture extruded pea protein isolate.