Expanded-Bed Adsorption of Proteins Using Ion-Exchangers

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Abstract
The use of expanded beds of ion-exchange adsorbents for the adsorption of proteins from feedstocks containing whole cells is described. Such feedstocks can be applied to the bed without prior removal of particulate material by centrifugation or filtration, thus showing considerable potential for this approach in simplifying downstream processing flow-sheets. Stable, expanded beds can be obtained using simple equipment adapted from that used for conventional packed bed adsorption and chromatography processes. Ion-exchange adsorbents are likely to be chosen for such separations as a result of the robustness of the ion-exchange groups to cleaning and sanitization protocols. Frontal analysis involving the measurement of breakthrough curves indicates that the adsorption performance of an expanded bed is similar to that achieved when the same amount of adsorbent is used in a packed configuration at the same volumetric flow-rate. In addition, the adsorption performance of an expanded bed of a cation exchanger was not diminished when adsorption was carried out in the presence of high concentrations of cells. However, the performance of similar beds of anion exchangers was found to be reduced under some conditions depending on the type of cells, their concentration, and their age. The results from the expanded bed adsorption experiments were consistent with those from batch adsorption which showed that the adsorption characteristics of the anion exchangers were diminished in the presence of cells in contrast to results with a cation-exchanger system where little deterioration in performance was noted. The results suggest that cation exchangers might be expected to be of more use for expanded bed adsorption in the presence of cells.