Chair for Food Process Engineering and Dairy Technology, Weihenstephaner Berg 1, D-85354 Freising-Weihenstephan, Germany.
J Phys Chem B. 2011 Mar 17;115(10):2349-59. doi: 10.1021/jp107622d. Epub 2011 Feb 22.
Caseins form heterogeneous micelles composed of three types of disordered protein chains (α, β, κ), which include protein-bound calcium phosphate particles. We probe the stability limits of the micelle by applying hydrostatic pressure. The resulting changes of the size distribution and the average molecular weight are recorded in situ with static and dynamic light scattering. Pressure induces irreversible dissociation of the micelles into monomers above a critical value depending on their size. The critical pressure increases with temperature, pH, and calcium concentration due to the interplay of hydrophobic and electrostatic interactions. The pressure transition curves are biphasic, reflecting the equilibrium of two micelle states with different stability, average size, entropy, and calcium bound. The fast process of pressure dissociation is used to probe the slow equilibrium of the two micelle states under various conditions. Binding and release of β-casein from the micelle is suggested as the molecular mechanism of stabilization associated with the two states. In situ FTIR spectroscopy covering the P-O stretching region indicates that bound calcium phosphate particles are released from serine phosphate residues at pressures above 100 MPa. The resulting imbalance of charge triggers the complete decomposition of the micelle.
-caseins 形成由三种无序蛋白质链（α、β、κ）组成的异质胶束，其中包括与蛋白质结合的磷酸钙颗粒。我们通过施加静水压力来探测胶束的稳定极限。通过静态和动态光散射，原位记录了大小分布和平均分子量的变化。在超过临界值的压力下，胶束会不可逆地解离成单体，这取决于它们的大小。由于疏水相互作用和静电相互作用的相互作用，临界压力随温度、pH 值和钙离子浓度的升高而升高。压力转变曲线呈双相性，反映了两种具有不同稳定性、平均大小、熵和结合钙的胶束状态之间的平衡。快速的压力解离过程用于探测在各种条件下两种胶束状态的缓慢平衡。结合和β-casein 从胶束中的释放被认为是与两种状态相关的稳定的分子机制。涵盖 P-O 伸缩区域的原位傅里叶变换红外光谱表明，在 100 MPa 以上的压力下，结合的磷酸钙颗粒从丝氨酸磷酸酯残基中释放出来。电荷的不平衡引发了胶束的完全分解。
