Effect of multi-frequency power ultrasound (MFPU) pretreatments on the degree of hydrolysis (DH) and mechanism of casein during alcalase enzymolysis was investigated. Results showed that MFPU pretreatment in tri-frequency 20/40/60 kHz mode significantly (p < 0.05) improved the DH value of casein. Variation of intrinsic fluorescence spectrum indicated the unfolding and degradation of casein occurred after MFPU pretreatment. Fourier transform infrared spectra showed that α-helix and β-sheet content of MFPU pretreated casein decreased, while β-turn and random coil content increased. Surface topography and nanostructures of caseins were found modified after MFPU pretreatments by the analysis of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The SEM analysis also indicated that the enzymolysis residues of casein pretreated by MFPU were smaller than untreated samples. In conclusion, the MFPU can be used as an efficient pretreatment method to promote the enzymolysis of casein.

中文翻译：

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多频功率超声（MFPU）处理对酪蛋白酶水解的影响。

研究了多频功率超声（MFPU）预处理对alcalase酶解过程中酪蛋白水解程度（DH）和作用机理的影响。结果表明，MFPU预处理在三频20/40/60 kHz模式下（p <0.05）显着提高了酪蛋白的DH值。固有荧光光谱的变化表明酪蛋白的展开和降解发生在MFPU预处理之后。傅里叶变换红外光谱表明，MFPU预处理的酪蛋白的α-螺旋和β-片层含量降低，而β-转角和无规卷曲含量增加。通过扫描电子显微镜（SEM）和原子力显微镜（AFM）的分析，发现MFPU预处理后酪蛋白的表面形貌和纳米结构得到了修饰。SEM分析还表明，MFPU预处理的酪蛋白的酶解残留量小于未处理的样品。总之，MFPU可以用作促进酪蛋白酶解的有效预处理方法。