Preliminary study of binary protein adsorption system and potential bioseparation under homogeneous field of shear in airlift biocontactor

Abstract

This paper investigates the bioseparation of binary protein mixtures using polystyrene based anion exchange resin. Adsorption experiments were conducted in batch mode using draft-tube internally recirculate dair lift biocontactor in comparison with the conventional shake flask batch adsorption equilibrium experiments. Binary protein mixtures contained bovine serum albumin (BSA) and bovine haemoglobin (BHb) at different initial fractions. Results from single solute adsorption experiments in biocontactor showed that both proteins were equally adsorbed onto the resin with equilibrium reached in an equal time period. This represents similar affinities towards the negatively charged resin surface, although BSA was expected to adsorb through specific forces. Adsorption results showed that BSA has hindered the BHb adsorption in the biocontactor, although adsorption of both proteins was equally hindered in the shake flasks adsorption experiments. Moreover, adsorption of BHb was inhibited up to 29% in the presence of BSA compared to the adsorption of BHb from a solution containing single solute of BHb at the same initial concentration. Similarly, the presence of BHb has hindered the adsorption of BSA by 59%. Adsorptions of both BSA and BHb from binary solution when each formed 75% initial fraction while the other protein formed the remaining 25% were relatively low with equilibrium reached in shorter time. Moreover, considerable amount of proteins remained in the solution, which demonstrates that multilayer adsorption most likely didn’t occur at the relatively small protein concentrations used in the present study. In general, the higher adsorption of BHb can also be related to the compressibility of its molecules which allowed for higher adsorption capacity. The homogeneous and lower shear environment in the airlift biocontactor compared to the other conventional batch adsorption in shake flask reduced the compressibility of BHb that caused higher BSA adsorption from binary solutions of BSA and BHb, which allowed for better bioseparation of both proteins.