Abascal Dulce, Lencki Robert W
Department of Food Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
Biotechnol Prog. 2004 Nov-Dec;20(6):1741-8. doi: 10.1021/bp0499350.
Ternary phase diagrams (TPDs) were constructed for aqueous beta-lactoglobulin solutions containing ethanol and (NH4)2SO4 at pHs of 7, 5, and 3 for temperatures between 20 and 70 degrees C. The addition of (NH4)2SO4 generally led to the production of a reversible precipitate, a transformation that was not strongly influenced by temperature or pH. In contrast, at pH 7 and 20 degrees C, ethanol concentrations >12% led to the formation of a molten-globule structure, which gelled at protein concentrations >10%. Destabilization of beta-lactoglobulin structure occurred at lower ethanol concentrations as temperature was increased, until at 70 degrees C, all solutions that were previously liquid at room temperature had transformed into a gel. At pH 5.0, near beta-lactoglobulin's isoelectric point, demixing dominated, leading to the creation of either irreversible precipitates or a paste-like microgel. Elevated temperatures caused the previously liquid morphology to transform into either a reversible aggregate or microgel. Solution behavior at pH 3 had characteristics of what was observed at pHs 7 and 5. At moderated protein and ethanol concentrations, a paste-like microgel was observed, whereas at higher ethanol concentrations, beta-lactoglobulin formed a gel. This work demonstrates how small changes in protein structure at the molecular level can have a dramatic effect on macroscopic morphology.
构建了含乙醇和硫酸铵的β-乳球蛋白水溶液在pH值为7、5和3、温度在20至70摄氏度之间的三元相图。添加硫酸铵通常会产生可逆沉淀，这种转变不受温度或pH值的强烈影响。相比之下，在pH值为7和20摄氏度时，乙醇浓度>12%会导致形成熔融球状结构，当蛋白质浓度>10%时会发生凝胶化。随着温度升高，在较低乙醇浓度下β-乳球蛋白结构就会发生去稳定化，直到70摄氏度时，所有之前在室温下为液体的溶液都转变为凝胶。在pH值5.0（接近β-乳球蛋白的等电点）时，分层占主导，导致形成不可逆沉淀或糊状微凝胶。温度升高会使之前的液体形态转变为可逆聚集体或微凝胶。pH值为3时的溶液行为具有在pH值7和5时所观察到的特征。在适度的蛋白质和乙醇浓度下，会观察到糊状微凝胶，而在较高乙醇浓度下，β-乳球蛋白会形成凝胶。这项工作证明了分子水平上蛋白质结构的微小变化如何能对宏观形态产生显著影响。
