Effects of ultrasonic-assisted pH shift treatment on physicochemical properties of electrospinning nanofibers made from rapeseed protein isolates

Electrospinning nanofibers (NFs) made from natural proteins have drawn increasing attention recently. Rapeseed meal is a by-product that rich in protein but not fully utilized due to poor properties. Therefore, modification of rapeseed protein isolates (RPI) is necessary to expand applications. In this study, pH shift alone or ultrasonic-assisted pH shift treatment was adopted, the solubility of RPI, along with the conductivity and viscosity of the electrospinning solution were detected. Moreover, the microstructure and functional characteristics of the electrospinning NFs, as well as the antibacterial activity of clove essential oil loaded-NFs were investigated. The tested parameters were remarkably improved after different treatments compared with the control, and synergistic effects were observed, especially under alkaline conditions. Hence, pH(12.5) + US showed the maximum value of solubility, conductivity, and viscosity, which was more than 7-fold, 3-fold, and almost 1-fold higher than the control respectively. Additionally, SEM and AFM images showed a finer and smoother surface of NFs after treatments, and the finest diameter of 216.7 nm was obtained after pH(12.5) + US treatment in comparison with 450.0 nm in control. FTIR spectroscopy of NFs demonstrated spatial structure changes of RPI, and improved thermal stability and mechanical strength of NFs were achieved after different treatments. Furthermore, an inhibition zone with a diameter of 22.8 mm was observed from the composite NFs. This study indicated the effectiveness of ultrasonic-assisted pH shift treatment on the physicochemical properties improvement and functional enhancement of NFs made from RPI, as well as the potential antibacterial application of the composite NFs in the future.