Controlling the rejection of protein during membrane filtration by adding selected polyelectrolytes

Electrostatic interactions among the charged groups on proteins and/or between proteins and other solutes significantly affect the aggregation/deposition phenomena that induce fouling and decrease permeate flux during membrane purification of proteins. Such interactions can be turned into an advantage by e.g. addition of new charged species that are able to destabilize the interactions causing aggregation or by controlling the charges via pH.

The present study examined the effect of (1) addition of polyelectrolytes-polystyrene-co-acrylic acid (PS-co-AA) and pectin-, respectively, and (2) changing the pH, on the permeate flux and membrane transmission of bovin serum albumina (BSA) through a PVDF membrane. The addition of PS-co-AA to the feed solution resulted in significant increases of the BSA transmission at pH 7.4 as compared to the transmission of a pure BSA solution (1g/L).

The addition of pectin to BSA at pH 7.4 also resulted in higher permeate fluxes and improved BSA transmission, as compared to the individual solution of pectin or BSA. The BSA transmission decreased at lower pHs i.e. at 4.7 (isoelectric point of BSA) and 2 with each polyelectrolyte as the apparent interactions between the BSA and the polyelectrolyte favoured deposition and aggregation phenomena, resulting in higher fouling.

The results suggest that the addition of a polyelectrolyte to a protein solution at a certain pH can dramatically modify the profile of electrostatic interactions causing fouling, and can help enhance the performance of membrane filtration for fractionation/purification of a target protein by significantly reducing fouling and modifying rejection/selectivity.