Application of transglutaminase modifications for improving protein fibrous structures from different sources by high-moisture extruding

Plant proteins can be extruded under high moisture content (above 40 %) to form meat-like fibrous structures, which is the basis for meat-like substitute products. However, the proteins' extrudability from various sources remain challenging in terms of generating fibrous structures under combinations of high-moisture extrusion with transglutaminase (TGase) modifications. In this study, proteins from soy (soy protein isolate, SPI, and soy protein concentrate, SPC), pea (pea protein isolate, PPI), peanut (peanut protein powder, PPP), wheat (wheat gluten, WG), and rice (rice protein isolate, RPI) were texturized using high-moisture extrusion combined with transglutaminase (TGase) modifications to enact changes in protein structure and extrusion capabilities. The results showed that soy proteins (SPI or SPC) responsed to torque, die pressure and temperature during extrusion, and this phenomenon was more pronounced at a higher protein content (SPI). In contrast, rice protein exhibited poor extrudability, leading to large losses of thermomechanical energy. TGase significantly affects the orientation of protein fibrous structures along the extrusion direction by impacting the rate of protein gelation during the high-moisture extrusion process, with the impact mainly occurring in the cooling die. Globulins (mainly 11S) played a major role in forming fibrous structures and the aggregation of globulins or reduction of gliadins under TGase modification impacted the orientation of the fibrous structure along the extrusion direction. Some thermomechanical treatment during high-moisture extrusion results in protein conversion from compact structure into more extended or stretched state, and the increase of random coil structures for proteins derived from wheat and rice would lead to these looser structures in the extrudates. Thus, TGase can be combined with high-moisture extrusion to regulate the formation of plant protein fibrous structures, dependent on the specific protein source and content.