Enzymatic double crosslinking strategy: remodeling of pea protein isolate hydrogels through transglutaminase and gelatin modification to redesign their functional properties.

Pea protein isolate (PPI) is rich in essential amino acids and exhibits low allergenicity; nevertheless, its poor gelation performance constrains its use in gel-based systems. To overcome this limitation, this study introduced gelatin (GEL) to modify pea protein isolate and constructed a double-crosslinked composite hydrogel based on a plant-animal protein combination via transglutaminase (TGase). The effects of different GEL/PPI ratios on the structure, mechanical properties, thermal stability, and swelling behavior of the hydrogels were investigated. The results showed that TGase effectively mediated covalent cross-linking between GEL and PPI. As the proportion of PPI increased, the hardness, gel strength, fatigue resistance, and shape recovery of the hydrogels decreased. All hydrogels demonstrated a high water content (>80%), and the incorporation of GEL significantly enhanced the water-holding capacity. SEM observation revealed that the hydrogels displayed a honeycomb-like porous structure. With increasing PPI content, the pores became smaller, the pore walls thickened, and the structural density increased. TGA and DSC analyses indicated that all hydrogels possessed good thermal stability. The swelling capacity decreased with the introduction of PPI, and all gels conformed to the Schott second-order kinetic model. XRD patterns suggested that all gel samples were predominantly amorphous in structure. These findings demonstrate that double-crosslinked PPI can produce hydrogels with higher mechanical strength, water-holding capacity, and stability, thereby improving the functional properties of PPI. This study provides a theoretical basis for developing novel edible hydrogels.