The study compared the effects of applying ultrasound (20 kHz, 200/600W, 10 min) before or after heating (100 °C, 20 min) on the physicochemical and emulsifying properties of soy protein isolate (SPI) under the same conditions. The results showed that ultrasound generally reduced the particle size of thermally induced soluble protein aggregates and increased protein solubility as the content of surface sulfhydryl groups increased. Ultrasound also increased the surface hydrophobicity, absolute value of the ζ-potential, and the change of protein tertiary structure and facilitated the reduction or restoration of changes in the secondary structures of protein caused by heating, possibly producing the better emulsifying properties observed in the samples treated by ultrasound. Most importantly, ultrasound treatment before heating led to the soluble protein aggregates showing the most molten globule-like conformation and having a homogeneous particle size, which was significantly different from the particle size distribution profile of the samples sonicated after heat treatment. Protein subjected to this combination treatment at a high ultrasonic power displayed the best emulsifying activity and emulsion stability. The findings suggest that the ultrasonic modification of protein molecules before heating is better than attempting remediation after heat treatment.

中文翻译：

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前/后超声对形成熔融球状构象和改善热诱导大豆蛋白聚集体乳化性能的影响

该研究比较了在相同条件下，在加热（100°C，20 分钟）之前或之后应用超声波（20 kHz，200/600W，10 分钟）对大豆分离蛋白 (SPI) 的理化和乳化特性的影响。结果表明，随着表面巯基含量的增加，超声波通常会减小热诱导可溶性蛋白质聚集体的粒径并增加蛋白质的溶解度。超声波还增加了表面疏水性、ζ-电位的绝对值和蛋白质三级结构的变化，并促进了加热引起的蛋白质二级结构变化的减少或恢复，可能在样品中观察到更好的乳化性能通过超声波治疗。最重要的是，加热前的超声处理导致可溶性蛋白质聚集体显示出最熔融的球状构象并具有均匀的粒径，这与热处理后超声处理的样品的粒径分布曲线显着不同。在高超声功率下进行这种组合处理的蛋白质显示出最好的乳化活性和乳液稳定性。研究结果表明，加热前对蛋白质分子进行超声修饰比在热处理后尝试修复效果更好。在高超声功率下进行这种组合处理的蛋白质显示出最好的乳化活性和乳液稳定性。研究结果表明，加热前对蛋白质分子进行超声修饰比在热处理后尝试修复效果更好。在高超声功率下进行这种组合处理的蛋白质显示出最好的乳化活性和乳液稳定性。研究结果表明，加热前对蛋白质分子进行超声修饰比在热处理后尝试修复效果更好。