Formation of a transparent soy protein hydrogel: Controlled thermal aggregation of protein using glutaminase

Plant protein-based hydrogels have enormous potential applications, and their great functional properties and sustainability are considered the best alternatives to reduce the environmental burden of animal protein resources. However, heat-induced plant protein-based hydrogels often exhibit a rough and opaque network structure, limiting their application in various scenarios where gel transparency is crucial. In this study, transparent hydrogels were successfully prepared using deamidated soy protein isolate (SPI) modified by protein-glutaminase (PG). Compared with the non-transparent SPI hydrogel, the deamidated SPI hydrogel possessed a soft and intricate chain-like network, exhibiting excellent light transmittance and certain mechanical strength. The results indicated that deamidation treatment unfolded the structure of SPI, shifting the protein conformation from ordered to disordered, and leading to the transformation of large insoluble protein aggregates into small soluble aggregates. In addition, deamidation treatment effectively inhibited the thermal aggregation rate and aggregation counts of SPI. This was attributed to the conversion of glutamine to glutamic acid, which enhanced the electrostatic repulsion between protein molecules. The present work offers a promising approach for preparing highly transparent plant protein-based hydrogels, which are conducive to developing the next generation of plant protein-based functional materials to replace existing petroleum-based materials.