Thermal aggregation and gelation behaviors of glucono-δ-lactone-induced soy protein hydrolysate gels: Effects of protein and coagulant concentrations

In this study, a novel acid-induced heat-set soy protein hydrolysate (SPH) gel was successfully developed. The effects of protein (7 and 8 wt%) and glucono-δ-lactone (GDL, 4, 6, 8, and 10 wt%) concentrations on its aggregation and gelation behaviors were investigated by evaluating the structural, rheological, textural, and physical properties of the SPH gel. The structural properties revealed that GDL promoted the formation of SPH aggregates and gels, primarily via disulfide bonds and hydrophobic interactions, which were closely related to the unfolding of the protein structure, exposed hydrophobic groups, decreased protein solubility, and increased particle size and turbidity during the heating process. Subsequently, the gelling properties demonstrated that acidification with GDL (4-8 wt%) significantly improved the viscosity, viscoelasticity, water-holding capacity, and stiffness of the network structures, decreased their hardness and springiness, and facilitated the formation of well-supported, soft-stiff gels, particularly for those made with 8 wt% protein. In addition, the changes in relaxation time measured via low-field nuclear magnetic resonance and magnetic resonance imaging confirmed that the SPH gels effectively retained water that was trapped in the gel network by strengthening the binding between water and protein molecules. The research could provide useful gelling technique for the protein hydrolysate products.