A novel approach for lysozyme and ovotransferrin fractionation from egg white by radial flow membrane adsorption chromatography: Impact of product and process variables

Fractionation of egg white proteins like lysozyme and ovotransferrin is an option to separately exploit the functionalities of the individual fractions. Methods for egg white protein fractionation published so far imply limitations either with regard to the used substrate (precipitated, mucin-free egg white) or the chromatographic system (packed bed columns). Thus, the aim of the present study was isolate lysozyme as well as ovotransferrin with a process that overcomes these limitations. Therefore, egg white was pre-treated with high-pressure homogenization to reduce its viscosity without losing proteins. Additionally, to avoid the diffusion limitations existing in common ion exchange processes, adsorptive membranes were used as stationary phase. In the first step of the fractionation, lysozyme was separated by a cation exchange process. Thereby, the effect of pH, conductivity and elution profile were determined. Using a fractionation pH of 9.8 and a sample conductivity of 7.8 mS cm(-1) resulted in a lysozyme purity of 96% and a yield of 99%. Thus, a complete binding of the target protein is possible. In the second step, the flow through resulting from the lysozyme fractionation was taken as substrate for the subsequent ovotransferrin fractionation via cation exchange. With the application of a fractionation pH of 4.9 an ovotransferrin purity of 84% and a yield of 97% were achieved. Thus, the two-stepped cation exchange process resulted in a purification factor of 21 for lysozyme and 5 for ovotransferrin. Further, the achieved yields and purities were shown to be flow rate independent using radial flow membrane adsorbers. Hence, the maximal possible flow rate can be used, whereby process time and costs are reduced. This is an essential aspect regarding scale-up to industrial level. Summing up, it was possible to fractionate lysozyme as well as ovotransferrin from the high-pressure homogenized egg white using adsorptive membranes with high purity and yield. Hence, radial flow membrane adsorbers offer a suitable possibility for egg white protein fractionation. (C) 2016 Elsevier B.V. All rights reserved.