超声处理对牛乳酪蛋白结构及抗原性的影响

利用超声波处理牛乳致敏蛋白α-酪蛋白（casein，CN）和β-CN，结合十二烷基硫酸钠-聚丙烯酰胺凝胶电泳、圆二色光谱、荧光光谱及酶联免疫吸附测定等方法分析α-CN和β-CN结构和抗原性的变化。结果表明：随着超声波功率的增大，α-CN的分子质量无显著性变化，β-CN在600 W时发生聚集，两种酪蛋白羰基含量上升，自由巯基含量先下降后回升，在500 W时达到最低，疏水性则呈现与自由巯基含量相反的规律；二级结构中，α-螺旋结构经超声处理后其相对含量减少，无规卷曲相对含量随着超声功率先增加后降低，功率为500 W时相对含量最高，β-折叠的相对含量变化趋势则与无规卷曲相反，这表明超声波处理破坏了酪蛋白的高级结构；随着超声功率的增强，抗原性呈现先升高后降低的趋势，其中500 W时抗原性最高，与酪蛋白疏水性及无规卷曲结构相对含量呈正相关，与β-折叠结构的相对含量呈现负相关。超声处理酪蛋白在影响蛋白构象及结构的同时改变其抗原性，且抗原性与疏水性及无规卷曲相对含量相关。

Effect of Ultrasonic Treatment on the Structure and Antigenicity of Bovine Caseins

In this study, changes in the structure and antigenicity of the milk allergenic proteins α-casein (α-CN) and β-casein (β-CN) after ultrasonic treatment were investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, circular dichroism (CD) spectroscopy, fluorescence spectroscopy and enzyme-linked immunosorbent assay (ELISA). The results showed that with the increase of ultrasonic power, the molecular mass of α-CN did not change significantly, β-CN aggregated at 600 W; the carbonyl contents of the two caseins increased, and the free sulfhydryl contents decreased first and then rose after reaching a minimum value at 500 W, while the trend was opposite to that of hydrophobicity. The proportion of α-helical secondary structure was reduced after sonication, and the proportion of random coil initially increased with ultrasonic power up to 500 W and then decreased; this trend was opposite to that of β-sheet content, indicating that ultrasonic treatment could destroy the structure of casein. As the ultrasonic power increased, the antigenicity first increased, reaching a maximum level at 500 W, and then decreased. The hydrophobicity of caseins was positively correlated with changes in random coil content, but negatively correlated with changes in β-sheet content. Sonication could affect protein structure conformation while altering the antigenicity of caseins, which was associated with changes in hydrophobicity and random coil content.