Ultrasound-regulated fibrillation of arachin: Structural characteristics, foaming and emulsifying properties

Ultrasound pretreatment can facilitate the protein fibrillation and change the structures of amyloid-like fibrils. However, there is little information concerning on the ultrasound regulation of protein fibrillation during the specific fibrillation process. In this study, ultrasound treatment (20% and 40% amplitudes) is applied to regulate the fibrillation of arachin from the lag phase, extension phase and plateau phase, respectively. The structural characteristics, foaming and emulsifying properties of the arachin amyloid-like fibrils (AFs) were investigated. The results showed that the maximum ThT fluorescence intensity of the AF-20%-2 h was 1.68 times higher than that of the AF without ultrasound regulation. Meanwhile, the far-ultraviolet CD result proved that the AF-20%-2 h and the AF-40%-2 h had higher content of β-sheets. The spectroscopy measurement results of intrinsic fluorescence, near-ultraviolet CD, and UV confirmed that the ultrasound treatment promoted the exposure of more Trp and Tyr residues on the surface of AFs, particularly for the AF-20%-2 h and the AF-40%-2 h. Moreover, a lower zeta potential, higher surface hydrophobicity and protein flexibility were observed in the AF-20%-2 h, making it better to adsorb on the air/water and oil/water interfaces. Therefore, the AF-20%-2 h showed higher foaming ability, foaming stability, emulsifying ability and emulsifying stability than other AFs. These findings can provide valuable insights into the ultrasound-regulated fibrillation of proteins.