We investigated the effect of ultrasound-assisted pH shift treatment on the micro-particle, molecular, and spatial structure of rapeseed protein isolates (RPI). Various ultrasonic frequency modes (fixed, and sweep) was used. Protein characterization by the indexes: particle size, zeta potential, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), scanning electron microscopy (SEM), free sulfhydryl (SH), surface hydrophobicity (Ho), Fourier transform infrared Spectrum (FTIR) and fluorescence intensity was studied to elucidate the changes in solubility and structural attributes of RPI. The results showed that ultrasonic frequency and working modes substantially altered the structure, and modified the solubility of RPI. Ultra + pH mode at fixed frequency of 20 kHz had the best effect on the solubility of RPI. Under the condition of ultra + pH mode, 20 kHz at pH 12.5, solubility, compared to control, increased from 8.90% to 66.84%; and the change in molecular structure of RPI was characterized by smaller particles (from 330.90 to 115.77 nm), high zeta potential (from −17.95 to −14.43 mV, p < 0.05), and increased free sulfhydryl (from 11.63 to 24.50 µmol/g) compared to control. Likewise, surface hydrophobicity increased (from 2053.9 to 2649.4, p < 0.05), whilst ɑ-helix and random coil decreased (p < 0.05), compared to control. The fluorescence spectroscopy and FTIR spectroscopy showed that the secondary and tertiary structure of the RPI were altered. These observations revealed that changes in RPI structure was the direct factor affecting solubility. In conclusion, ultrasound assisted pH shift treatment was proven to be an effective method for the modification of protein, with promising application in food industry.

我们调查了超声辅助pH移位处理对菜籽蛋白分离株（RPI）的微粒，分子和空间结构的影响。使用了各种超声频率模式（固定和扫描）。通过以下指标对蛋白质进行表征：粒径，ζ电位，十二烷基硫酸钠聚丙烯酰胺凝胶电泳（SDS-PAGE），扫描电子显微镜（SEM），游离巯基（SH），表面疏水性（Ho），傅立叶变换红外光谱（FTIR）研究了荧光强度以阐明RPI的溶解度和结构属性的变化。结果表明，超声频率和工作模式大大改变了结构，并改变了RPI的溶解度。在20 kHz固定频率下的Ultra + pH模式对RPI的溶解度影响最大。在Ultra + pH模式下，pH值为12.5时为20 kHz，与对照相比，溶解度从8.90％增加到66.84％；RPI分子结构的变化以较小的颗粒（从330.90至115.77 nm），高的ζ电位（从-17.95至-14.43 mV，p  <0.05），并且与对照组相比，游离巯基增加（从11.63至24.50 µmol / g）。同样，与对照相比，表面疏水性增加（从2053.9增加到2649.4，p  <0.05），而α-螺旋和无规卷曲减少（p  <0.05）。荧光光谱和FTIR光谱表明，RPI的二级和三级结构发生了变化。这些观察结果表明，RPI结构的变化是影响溶解度的直接因素。综上所述，超声辅助pH移位处理被证明是一种有效的蛋白质修饰方法，在食品工业中具有广阔的应用前景。