Crystallization Characteristics Of Proteins From Bovine Whey

Bovine whey contains many proteins, including immunoglobulin(IgG), bovine serum albumin(BSA), lactoferrin, lactoperoxidase. These proteins can be obtained by means of chromatography. However, the chromatography has its own limitations, including excessively high cost of devices and consumptive material, as well as excessive requirement of operation. Then, an alterlative technology is inevitably needed. Crystallization is another good choice due to its low cost and simple operation. The aim of this thesis is to explore the means by crystallization for the separation of bioreactive proteins from bovine whey. The suitable conditions and the crystallization behavior of bovine whey by this method were investigated, which could be employed as the foundation for the crystallization separation of whey proteins.Firstly, to verify whether this method can be used effectively to separate the whey proteins or not, the system of BSA+ salts+water was used as a sample to study the protein solubility and nuclear data in various solutions containing 1-3 M Na Cl, pH 4.7-8.0 and 1.0-3.0 mg/mL BSA. Then, images of BSA crystals(2.5 mg/mL BSA, p H 7.0, 1 M NaCl) were obtained and the impurities within these BSA crystals were analyzed. The solid-liquid equilibrium principle was utilized and semi-empirical correlation equations for the description of the equilibrium of protein solubility were obtained. The parameters regarding these equations were determined by matching the experimental data.The crystallization conditions of bovine whey system were investigated experimentally using the bovine whey system. The content of IgG in the supernatant of whey after crystallization by freezing was found to be decreased significantly at pH 7.0. The ratio of each content of proteins in the whey was not changed obviously with the increase of salt concentration at other pH values. Therefore, pH 7.0 can be used as the valid pH value for the protein crystallization and IgG could be considered as the target protein.The crystallization behaviors of whey for the solution containing 0.5 and 2.0 M NaCl at pH 4.7 and 7.0 were investigated by inverted fluorescence microscope and the BSA+salts+water system was employed as the counterpart at the same conditions for comparison purpose. Different morphology types of monocrystals, including orthorhombic crystals, tetragonal crystals and rhombus crystals, were observed. Besides, the association of the crystals having the same shape was also observed, together with other kinds of associations. Finally, crystals with an uniform particle size distribution were observed in the salt solution containing 0.5 M NaCl at pH 7.0. The results are expected to be useful in the invesitigation of crystallization kinetics and helpful in the development of a new protein separation process for the isolation of bioreactive proteins from bovine whey.