超声处理对牛乳酪蛋白结构及抗原性的影响

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

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。

In this study,changes in the structure and antigenicity of the milk allergenic proteinsα-casein(α-CN)andβ-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 ofα-CN did not change signi ficantly,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 ofα-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 ofβ-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 inβ-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.