Improving gel properties of soy protein isolate through alkaline pH-shifting, mild heat treatment, and TGase cross-linking

Improving the functional properties of soybean protein isolate (SPI) is essential for expanding its applications in food-related fields, given its poor solubility and gelation. This study investigated the effect of alkaline pH-shifting and mild heating on the structure of SPI, as well as the gel properties after TGase cross-linking. Solubility of SPI increased with increasing alkalinity from pH 7.0 to 12.0 at 25 °C, accompanied by decreased particle size and increased surface hydrophobicity. At pH 12.0 and 50 °C, SPI showed the highest solubility, smallest particle size, and best surface hydrophobicity. Intrinsic fluorescence spectra revealed that the protein structure unfolded after combined treatment, exposing more hydrophobic groups. TGase cross-linking modified SPI exhibited significantly increased gel hardness and water holding power. Therefore, alkaline pH transfer combined with mild heating treatment has great potential for generating functional modified SPI and provides a simple and easy method for preparing SPI with diverse gel and structural properties.