Impact of the substrate viscosity, potentially interfering proteins and further sample characteristics on the ion exchange efficiency of tangential flow membrane adsorbers

The use of tangential flow membrane adsorbers is a highly recommendable option for chromatographic separations of particle containing substrates or substrates with high viscosities, like egg white. Due to the direction of the convective flow in this stationary phase, the sample is not required to be filtered. Our earlier study investigated the flow conditions of tangential flow membrane adsorbers. There, it became clear that the flow is based on a mix of convective and diffusive mass transfer. The diffusive component of the transport of the target proteins into the membrane structure depends on the viscosity of the medium according to the Stokes--Einstein equation. Therefore, it was the aim of the present study to assess the impact of viscosity on the ion exchange efficiency. Further, the amount of the main target protein of egg white, the bio-functional protein lysozyme, is relatively low compared to the other major egg white proteins. As a high amount of non-target proteins in the substrate can also interfere with the diffusional mass transfer of the target protein, it was an additional aim to understand the impact of the substrate composition on the lysozyme adsorption. It was shown that the effective diffusion coefficients (Deff) as well as the maximal binding capacities (qmax) strongly depend on the egg white viscosity. Applying natural egg white with a mean viscosity of 70mPa s, a qmax of 0.14mgcm$-$2 with a Deff of 1.5$\times$10$-$7 cm2 s$-$1 were achieved. If the viscosity of egg white was reduced by means of a mechanical pre-treatment, qmax was increased to 0.49mgcm$-$2 with a Deff of 9.2$\times$10$-$7 cm2 s$-$1. Consequently, the adsorption efficiency strongly depends on the substrate viscosity. Additionally, the impact of high amounts of non-target proteins in egg white on the adsorption of the target protein lysozyme was analyzed. It was demonstrated that the other egg white proteins strongly interfere the lysozyme binding to the membrane (qmax of 0.49mgcm$-$2 compared to 0.65mgcm$-$2). This is probably due to steric effects and interactions between the proteins. Finally, it can be concluded that diffusion is an important transport mechanism of tangential flow membrane adsorbers, and if this is disturbed by inappropriate conditions, the process works less well.     «

The use of tangential flow membrane adsorbers is a highly recommendable option for chromatographic separations of particle containing substrates or substrates with high viscosities, like egg white. Due to the direction of the convective flow in this stationary phase, the sample is not required to be filtered. Our earlier study investigated the flow conditions of tangential flow membrane adsorbers. There, it became clear that the flow is based on a mix of convective and diffusive mass transfer...     »