Ultrasound regulates pea protein fibrillation: Impact on aggregation kinetics, physicochemical properties, structure and morphology

Ultrasonication can alter the structure of proteins and modify their physicochemical properties. However, there was little information concerning the ultrasound-induced protein fibrillation during the specific fibrillation process. In this study, ultrasound with different power densities (2.17, 2.39, 2.65, 3.19, and 3.73 W/mL) was applied to regulate the growth kinetics of the fibrillation process of pea protein isolates (PPI) at the beginning of fibrillation process (t0), the end of lag phase (t0.1) and the end of the exponential phase (t0.9). The morphology, physicochemical and structural properties of PPI, and the corresponding fibrils (PPIF) were investigated. The results showed that ultrasound treatments with power densities of 2.65, 3.19, and 3.73 W/mL at t0 accelerated fibrillation. The decreased hydrodynamic diameter and the higher proportions of β-sheet of PPI after ultrasonication indicated a disassociation of PPI agglomerates and a structure transformation, which may help PPI go through the lag phase. Ultrasound treatment increased the growth rate of PPIF with higher power density at t0.1 (3.73 W/mL) but lower power density at t0.9 (2.17 W/mL), which may be because appropriate ultrasound power broke protein oligomers into fragments as the template for fibril elongation, resulting in decreased hydrodynamic diameters and increased surface hydrophobicity. The morphology of ultrasound treated samples exhibited shorter contour lengths and higher flexibility than that of the control group, revealing the important role of ultrasound in regulating the protein fibrillation process.