Mechanism of high-moisture extruded protein fibrous structure formation based on the interactions among pea protein, amylopectin, and stearic acid

During high-moisture extrusion (HME) processing for plant protein texturization, the interactions among proteins, starch and lipids should determine the formation of fibrous structures, which has not been confirmed systematically. In this study, the mechanism of protein fibrous structure formation during HME processing (58% moisture) was investigated based on the intermolecular interactions among the pea protein, amylopectin and stearic acid. Results suggested that the amylopectin and stearic acid synergistically contributed to improve the fibrous structures such as the hardness and fibrous degree in pea protein extrudate. In the extruder barrel, the complexation among the protein with amylopectin and stearic acid gave rise to the formation of aggregates with higher thermal stability and delayed the formation of protein gel network. In the die, the amylopectin and stearic acid weakened the hydrogen bonds between proteins and hindered the aggregation of legumin and vicilin subunits. In the cooling zone and extrudate, the amylopectin and stearic acid promoted the formation of fibrous structures through an "anchor orientation and flexible cross-linking" mechanism. Namely, the stearic acid as anchors hindered the refolding of protein molecular chains, while the amylopectin promoted the rearrangement, cross-linking and aggregation of protein molecules. The amylopectin and stearic acid synergistically weakened the interaction forces between proteins and led to the formation of more flexible structures in aggregates, which was favorable for the orientation and formation of anisotropic fibrous structures in extrudates. This study provided a theoretical basis for the development and improvement of the plant-based meat substitutes.