Enhancement of physicochemical and techno-functional properties of soy protein isolate amyloid fibrils by moderate ultrasonic pretreatment

Plant protein can be functionally strengthened by its modification into amyloid fibrils, which has drawn growing interest. In this study, we investigated the effects of ultrasonic pretreatment on the fibrillation kinetics, physicochemical properties, and functional aspects of soy protein isolate amyloid fibrils (SPF). Firstly, soy protein isolates (SPI) were subjected to ultrasonic pretreatment by regulating time and power under neutral conditions. Subsequently, the pretreated SPI was converted into SPF through acidic heating. The results indicated that ultrasonic pretreatment significantly improved surface hydrophobicity and solubility of SPI through ultrasound's cavitation and thermal effects. Thioflavin T fluorescence assay revealed SPF40 (450 W, 40 min) had the fastest growth rate, 104.23 % higher than SPF0 (without ultrasonic pretreatment), while SPF10 (450 W, 10 min) had the highest fibril yield, 20.97 % higher than SPF0. Physicochemical analysis showed that ultrasonic pretreatment accelerated the formation of SPF from SPI by exposing the surface hydrophobic groups, lowering the zeta potential, breaking down original fibrils into shorter fibrils, and altering the secondary structure from alpha-helices into beta-sheets. Morphological examination by transmission electron microscopy exhibited a higher maturation state, showing more rigid and straight fibrils structure in SPF10 compared to SPF0. Functionally, SPF with ultrasonic pretreatment had higher emulsifying activity than SPI and SPF0. Rheological analysis further confirmed SPF emulsions' better mechanical strength over SPI emulsions. Overall, this study demonstrates that ultrasonic pretreatment is an effective way to enhance the formation and properties of SPF, which can be further applied to developing advanced protein products and novel functional food systems.