Zeta potential as a diagnostic tool to evaluate the biomass electrostatic adhesion during ion‐exchange expanded bed application

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Abstract
Expanded bed adsorption is an integrative technology in downstream processing allowing the direct capture of target proteins from biomass (cells or cell debris) containing feedstocks. Potential adhesion of biomass on the surface of adsorbent, however, may hamper the application of this technique. Since the electrostatic forces dominate the interactions between biomass and adsorbent, the concept of zeta potential was introduced to characterize the biomass/adsorbent electrostatic interactions during expanded bed application. The criterion of zeta potential evaluation proposed in the previous paper (Biotechnol Bioeng, 83(2):149–157, 2003) was verified further with the experimental validation. The zeta potential of intact cells and homogenates of four microorganisms (Escherichia coli, Bacillus subtilis, Pichia pastoris, and S.cerevisiae) were measured under varying pH and salt concentration, and two ion‐exchange adsorbents (Streamline DEAE and Streamline QXL) were investigated. The biomass transmission index (BTI) from the biomass pulse response experiments was used as the indicator of biomass adhesion in expanded bed. Combining the influences from zeta potential of adsorbent (ζa), zeta potential of biomass (ζb) and biomass size (d), a good relationship was established between the zeta potential parameter (−ζaζbd) and BTI for all experimental conditions. The threshold value of parameter (−ζaζbd) can be defined as 120 mV2 µm for BTI above 0.9. This means that the systems with (−ζaζbd) < 120 show neglectable electrostatic bio‐adhesion, and would have a considerable probability of forming stable expanded beds in a biomass suspension under the particular experimental conditions.