Department of Food Science, Rutgers University, 65 Dudley Road, New Brunswick, New Jersey 08901, USA.
J Phys Chem B. 2012 Oct 4;116(39):12057-64. doi: 10.1021/jp305709y. Epub 2012 Sep 24.
Zein is a corn prolamin that has broad industrial applications because of its unique physical properties. Currently, the high cost of extraction and purification, which is directly related to the dispersion of zein in different solvents, is the major bottleneck of the zein industry. Solution behaviors of zein have been studied for a long time. However, the physical nature of zein in different solvents remains unclear. In this study, small-angle X-ray scattering (SAXS), static light scattering (SLS), and rheology were combined to study the structure and protein-solvent interaction of α-zein in both acetic acid and aqueous ethanol solutions. We found that the like-dissolve-like rule, the partial unfolding, and the protonation of zein are all critical to understanding the solution behaviors. Zein holds an elongated conformation (i.e., prolate ellipsoid) in all solutions, as revealed from SAXS data. There is an "aging effect" for zein in aqueous ethanol solutions, as evidenced by the transition of Newtonian rheological profiles for fresh zein solutions to the non-Newtonian shear thinning behavior for zein solutions after storage at room temperature for 24 h. Such shear thinning behavior becomes more pronounced for zein solutions at higher concentrations. The SLS results clearly show that acetic acid is a better solvent to dissolve zein than aqueous ethanol solution, as supported by a more negative second virial coefficient. This is majorly caused by the protonation of the protein, which was further verified by the dissolution of zein in water (a nonsolvent for zein) with the addition of acids.
玉米醇溶蛋白是一种玉米蛋白，具有独特的物理性质，因此在工业上有广泛的应用。目前，其提取和纯化成本高，这与玉米醇溶蛋白在不同溶剂中的分散直接相关，是玉米醇溶蛋白行业的主要瓶颈。人们长期以来一直在研究玉米醇溶蛋白的溶液行为。然而，不同溶剂中玉米醇溶蛋白的物理性质仍不清楚。在这项研究中，小角 X 射线散射（SAXS）、静态光散射（SLS）和流变学相结合，研究了α-玉米醇溶蛋白在乙酸和水乙醇溶液中的结构和蛋白质-溶剂相互作用。我们发现，类似溶解的规则、玉米醇溶蛋白的部分展开和质子化对于理解溶液行为都是至关重要的。从 SAXS 数据可以看出，玉米醇溶蛋白在所有溶液中都呈现出拉长的构象（即长椭球体）。在水乙醇溶液中，玉米醇溶蛋白存在“老化效应”，这表现为新鲜玉米醇溶蛋白溶液的牛顿流变特性向室温下储存 24 小时后玉米醇溶蛋白溶液的非牛顿剪切变稀行为的转变。对于浓度较高的玉米醇溶蛋白溶液，这种剪切变稀行为更为明显。SLS 结果清楚地表明，乙酸是溶解玉米醇溶蛋白的更好溶剂，这得到了第二维里系数更负的支持。这主要是由于蛋白质的质子化，通过在非溶剂水中（即水）中添加酸来溶解玉米醇溶蛋白，进一步验证了这一点。
