Effects of pH on the Emulsifying Properties of Tilapia （Oreochromis niloticus） Myosin
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摘要: 【目的】探讨pH值对肌球蛋白乳化稳定性及界面蛋白组成和结构的影响。【方法】设定2.0、5.0、7.0、11.0等4种pH值，通过pH偏移法探究其对罗非鱼（Oreochromis niloticus）肌球蛋白乳化性的影响，采用高压均质法制备罗非鱼肌球蛋白-大豆油乳液，分析不同pH值条件下罗非鱼肌球蛋白乳液的稳定性、界面蛋白组成及分子结构的变化。【结果】pH为5.0时，肌球蛋白的乳化性最差，乳液粒径最大（P < 0.05），Zeta-电位绝对值最小（P < 0.05），界面蛋白α-螺旋含量最低，无规则卷曲含量最多，乳液在贮藏期内明显分层。调节pH值至2.0、7.0和11.0时，肌球蛋白的乳化活性与乳化稳定性增强，乳液贮藏7 d未分层。电泳结果显示，乳液体系中界面蛋白主要由肌球蛋白重链组成，pH 2.0和5.0时蛋白在界面发生交联聚集，而pH 7.0和11.0时蛋白在界面聚集少，与未经处理的肌球蛋白相比，乳液及界面吸附状态肌球蛋白的二级结构发生明显变化，α-螺旋含量减少（P<0.05）。比较而言，pH 11.0条件下，肌球蛋白乳液粒径最小（P < 0.05），界面蛋白分子结构部分展开，与油滴相互作用增强，肌球蛋白的乳化性最好。【结论】pH值的变化能诱导肌球蛋白分子结构及界面特性的改变，从而改善肌球蛋白的乳化性能。Abstract: 【Objective】 To study the effect of pH value on emulsifying properties of myosin 【Method】 Tilapia(Oreochromis niloticus)myosin-soybean oil emulsion was prepared by highpressure homogenization at four pH values (2.0, 5.0, 7.0, 11.0). The changes of emulsion stability, interfacial protein composition and molecular structure of myosin at different pH values were analyzed, and the effects of pH value on the molecular structure and interfacial characteristics of myosin were investigated. 【Result】 When the pH value was adjusted to 5.0, myosin had the worst emulsifying properties, the largest particle size (P < 0.05) and the smallest absolute value of Zeta-potential (P < 0.05), the least α -helix content of interfacial myosin in the emulsion, and the highest random coil content. And the emulsion was obviously stratified during storage. When adjusting the pH to 2.0, 7.0 and 11.0, the emulsifying activity and emulsifying stability of myosin were increased, the emulsion was not stratified after 7 days of storage. The results of electrophoresis showed that the interfacial proteins in the emulsion were mainly composed of myosin heavy chains. At pH 2.0 and 5.0, proteins were crosslinked and aggregated at the interface, while the aggregation of myosin at the interface was less at pH 7.0 and 11.0. Compared with untreated myosin, the secondary structure of treated myosin in emulsion and interface adsorption state was significantly changed, and the α -helix content was decreased (P < 0.05). In comparison, at pH 11.0, myosin had the best emulsifying properties, the particle size of myosin emulsion being the smallest (P < 0.05), and the molecular structure of the interfacial myosin was partially unfolded with the enhanced interaction between protein molecules and oil droplets. 【Conclusion】 The change of pH value can induce the changes in molecular structure and interface characteristics of myosin, which can improve the emulsifying properties of myosin.
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Key words:
- myosin /
- pH value /
- emulsion /
- emulsion stability /
- interfacial protein
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