A combined enzymatic and ionic cross-linking strategy for pea protein/sodium alginate double-network hydrogel with excellent mechanical properties and freeze-thaw stability

While pea protein (PeaP) is considered to be the plant protein with the most potential for use in plant-based meat products, it is limited by poor gel performance. To overcome this issue, a one-pot method was adopted to prepare a double-network (DN) hydrogel based on a transglutaminase-induced cross-linked network of PeaP and a physically cross-linked network of sodium alginate (SA). As SA concentration increased, the layered structure inside the hydrogel first converted into a porous honeycomb-like structure before forming a dense 3D network structure. Mechanical testing results suggested that the Young's Modulus of hydrogel increased from 2.1 MPa to 8.6 MPa at 80% strain as SA increased from 0% to 0.25%. This dense DN structure endowed the hydrogel with great fatigue resistance as well as excellent textural properties. Low-field nuclear magnetic resonance suggested that the DN hydrogel had a higher binding water content than PeaP single-network hydrogel, and showed good freeze-thaw stability. It is believed that this present work can give some insight into existing PeaP gel systems and inspire the development of more PeaP-based DN hydrogel with desired mechanical strength and freeze-thaw stability.