Effects of NaCl concentration and temperature on fibrillation, structure, and functional properties of soy protein isolate fibril dispersions

Food-grade material fibril is progressively recognized as an important fundamental area of current research to improve the functionality of foods. This work investigated the fibrillation of soy protein isolate (SPI) heated at different temperatures (80 and 95 °C) and NaCl concentration (0–320 mmol/L). The rheological and emulsifying properties were also analyzed, and the contribution of fibril structures was determined. ThT and FTIR assay indicated that the amount of soy protein isolate fibril (SPF) was independent of temperature, but the speed of SPI fibrillation was proportional to it. TEM showed the structure of fibrils was various. SPF formed at 80 °C was more flexible than 95 °C. With the increase of NaCl concentration, the diameter of SPF formed at 80 °C was thicker, and the fibrils were entangled together at the excessive salt concentration (>80 mmol/L). The transparent local gelation of fibrils was observed at 95 °C, and it imparted a higher viscosity. Moreover, the emulsifying property of SPF was significantly increased due to the quick absorption and high viscosity onto the oil-water interface. The results also suggested that flexible fibrils can be faster to adsorb to the droplet surface. These findings may inspire the application of protein fibril.