Ultrasonic-assisted production of okara protein isolate amyloid fibrils from plant-based by-products: Structural and morphological characteristics

The amyloid fibrillization technology of plant proteins points to the development of new functional foods using plant processing by-products. Okara protein isolate (OPI) is such a sustainable protein resource from soybean processing, with huge output and rich nutrition. This study employed ultrasonic pretreatment to enhance the fibrillation capacity of OPI. Following ultrasonic pretreatment, heating at 90 °C under pH 2 conditions for 9 h yielded amyloid fibrils with high conversion rates, validated through ThT fluorescence, SDS-PAGE, and AFM techniques. UV and FTIR analyses confirmed the formation of amyloid fibril structures rich in characteristic cross-β-sheets. Furthermore, this study revealed that ultrasonic pretreatment may partially unfold proteins and expose hydrophobic regions, subsequently promoting amyloid fibril aggregation during incubation. Conversely, excessive ultrasonic pretreatment may lead to over-unfolding of protein structures, resulting in structural instability that hinders amyloid fibril aggregation. This research not only elucidates the mechanism by which ultrasound regulates amyloid fibril formation but also provides a practical solution for the application of soybean residue protein in the field of food science.