Transforming Soy Proteins Into Nanoporous Aerogels Using Supercritical Carbon Dioxide Drying

ABSTRACT This study investigated the formation and characterization of aerogels from soy protein isolate (SPI) at different pHs (6–10) using supercritical carbon dioxide (SC‐CO 2 ) drying. The extraction yield of proteins was 33% with 92% purity. The formed SPI hydrogels and aerogels were characterized for their rheological properties, textural properties, morphology, crystallinity, chemical structure, thermal stability, and solubility. The gels formed at pH values ranging from 7.0 to 10.0 were strong, and all exhibited shear‐thinning behavior. The hardness of the gels increased with the increase in pH from 7.0 to 10.0. The resulting SPI aerogels upon SC‐CO 2 drying showed outstanding properties, such as surface areas of 222–278 m 2 /g, pore sizes of 8–11 nm, and pore volumes of 1.88–3.13 cm 3 /g. Their densities were ~0.21 g/cm 3 with high porosities of ~83%. Further, scanning electron microscopy images of aerogels showed three‐dimensional open porous structures, where the structures were more heterogeneous at higher pH values, leading to a higher surface area. X‐ray diffraction and Fourier transform infrared spectroscopy data provided information about the crystallinity and changes in the chemical structure of proteins, respectively. The main thermal degradation peak for aerogels was ~295°C, which was slightly lower than that for SPI powder at 303°C. The water solubility of SPI powder increased with the formation of aerogels from 17%–19% to 30%–36%. Overall, this study provides one of the first reports on generating SPI aerogels with high surface areas for their potential use in food, pharmaceutical, and biomaterial industries.