The influence of homogenisation conditions on biomass-adsorbent interactions during ion-exchange expanded bed...

Expanded bed adsorption (EBA) is an integrative step in downstream processing allowing the direct capture of target proteins from cell-containing feedstocks. Extensive co-adsorption of biomass, however, may hamper the application of this technique. The latter is especially observed at anion exchange processes as cells or cell debris are negatively charged under common anion exchange conditions. The restrictions observed under these conditions are, however, directly related to processing steps prior to fluidised bed application. In this study, it could be shown that the effective surface charge of cell debris obtained during homogenisation is closely related to the debris size and thus to the homogenisation method and conditions. The amount and thus effect of cells binding to the adsorbent could be significantly decreased when optimising the homogenisation step not only towards optimal product release but towards a reduction of debris size and charge. The lower size and charge of the debris results not only in a reduced retention probability but also, in a lower collision probability between debris and adsorbent. The applicability was shown in an example where the homogenisation conditions of E. coli were optimised towards EBA applications. In a previous report (Reichert et al., 2001) studying the suitability of EBA for the capture of formate dehydrogenate from E. coli homogenate the pseudo affinity resin Streamline Red was identified as the only suitable adsorbent. The new approach, however, led to a system where anion exchange as capture step became possible, however, to the cost of binding capacity.