Glucono-δ-lactone-induced gel fabrication of soybean protein isolate derived from germinated soybean: Focusing on protein aggregation and gelation

We have previously reported that soybean germination increases the water-holding capacity (WHC) of glucono-δ-lactone (GDL)-induced soymilk gels while weakening their gel strength. However, the associated mechanism(s) underlying this decrease in gel strength remains unclear. Herein, we investigated the mechanisms underlying the effects of germination on soymilk gel formation. To this end, we prepared GDL-induced soybean protein isolate (SPI) gels. Germination-induced changes in the SPI structure and thermal aggregation behavior were examined. Subsequently, the gelation properties of the SPIs derived from germinated soybeans were investigated, including texture, WHC, microstructure, rheology, thermogravimetry, and intermolecular forces. Germination induced the production of small-molecule proteins and peptides in SPI. Additionally, the SPI structure unfolded, exposing hydrophobic groups on the surface and causing the protein structure to become increasingly disordered with increased germination time. Meanwhile, most of the newly formed small peptides (< 1.3 kDa) produced during germination did not contribute to gel formation. Mechanistically, as the hydrophobic interactions increased, the disulfide bonds decreased during protein pre-aggregation and gel formation. This interfered with the gel’s three-dimensional network structure development, decreasing SPI gel hardness, viscoelasticity, and thermal stability while increasing the WHC. These findings offer insights into the protein-level gelling mechanism of soymilk gels created with germinated soybeans, inform the development of innovative gelation technology, and advance the industrial development of germinated soybeans.