Formation and physicochemical properties of amyloid fibrils from soy protein

Amyloid-like fibrils from food proteins possess unique functional properties for food and many other uses. This study reports the effect of hydrolytic heating (pH 2.0, 85 °C, 0-24 h) and incubation times (0-7 days) on the formation and physicochemical properties of amyloid fibrils based on soy protein isolates (SPI). The SPI hydrolysates and fibrils were characterized through AFM, Thioflavin T (ThT) fluorescence, SDS-PAGE, FTIR, solubility, particle size, and DSC. Stable amyloid-like protein fibrils were formed with 8-10 h of hydrolytic heating at 85 °C followed by 3 days of incubation at room temperature, as observed under AFM and confirmed with ThT assay. The fibrils contained significantly higher amounts of regular secondary structures than SPI. Incubation of the hydrolysates led to a slight increase of average particle sizes. Protein solubility near the isoelectric point (approximately pH 4.8) increased with longer hydrolytic heating (0-24 h). The hydrolysates and fibrils exhibited better gelling properties than the SPI. The DSC results revealed that hydrolysates from longer hydrolytic heating times (12 and 24 h) possessed stronger aggregation potential during heat treatment. This study provides useful information to manipulate the formation of protein fibrils and will benefit future research to explore their potential applications.