Structural characterization of soy protein hydrolysates and their transglutaminase-induced gelation properties

Abstract

Soy protein hydrolates (SPHs) were produced by hydrolyzing soy protein isolate (SPI) for different times (5–180 min) using Alcalase, followed by cross-linking with transglutaminase (TGase) and their gelation capacity were then evaluated. The hydrolysis degree (DH) of SPHs increased from 1.37% to 6.61% as the increasing hydrolysis time from 5 min to 180 min. Compared to SPI, enzymatic hydrolysis enhanced the surface hydrophobicity and random coil structure, but decreased the free sulfydryl content, α-helix and β-turn structures of SPHs. Notably, the low hydrolysis (DH: 1.37–2.17%) improved the protein solubility, disulfide bond content and β-sheet structure, decreased the turbidity of SPHs solutions in comparison with those hydrolyzed highly (DH: 3.12–6.61%). In addition, the TGase-pretreated SPHs displayed typical weak gel-forming capacities upon acyl transfer and protein cross-linking. In contrast, low-hydrolyzed SPHs (DH: 2.17%) exhibited superior gelation behaviors, as confirmed by uniform networks with small cavities, larger relaxation time distribution, higher viscoelasticity and water-holding capacity of 54%. In general, TGase indeed promoted the gelation capacity of SPHs subjected to limited hydrolysis, which facilitates the application of SPHs in food formulation.