Effects of Ionic Environments on Bovine Serum Albumin Fouling in a Cross‐Flow Ultrafiltration System

Abstract

The influence of electrostatic interactions on membrane fouling during the separation of bovine serum albumin (BSA) from solution was studied in a crossflow ultrafiltration system. Experiments were carried out at different pH values between 3.78 and 7.46; and for different ionic strengths between 0.001 M and 0.1 M. The changes in permeate flux, cake layer resistance, zeta potentials of BSA and polyether sulfone (PES) membranes, and electrostatic interaction energies, were evaluated. At all of the ionic conditions studied, PES membranes are negatively charged. However, BSA molecules are either negatively or positively charged depending on the ionic environment. Whereas the cake layer resistance decreased with increasing pH and ionic strength, the permeate fluxes increased. The calculated electrostatic energy was a minimum at the isoelectric point (IEP) of BSA. However, at this point, the cake resistances corresponding to fouling at each ionic strength, were not minimized. Below the IEP of BSA, the electrostatic forces were attractive, while above the IEP, repulsive electrostatic forces were dominant. IntroductionMembrane processes are widely used in the separation and concentration of biomolecules in biotechnological processes. However, membrane fouling is an unavoidable consequence and one of the most serious considerations in the application of membranes [1]. Membrane fouling has often been explained through complicated physicochemical interactions between the membrane and the protein. Interactions between charged molecules and membrane surfaces may be classified into the following major contributions [2]: i) electrostatic interaction between the protein and the surfaces, and ii) hydrophobic dehydration of various parts of the protein molecules, structural rearrangements in the protein molecule and van der Waals interactions.The quantification of interactions between biomolecules and membranes is usually a major concern in studies on membrane fouling. Several attempts have been made to calculate the interfacial interaction energies between the protein and the membrane using well-established fundamental theories, such as the Derjaguin-Landau-Verwey-Overbeek (DLVO) and electrostatic double layer (EDL) theories [3][4][5][6]. A large number of these studies have been devoted to the interaction of the model protein bovine serum albumin (BSA) with polymeric membranes, since serum albumin is one of the most important proteins in blood plasma 1) . The ionic environment has a considerable impact on interfacial interactions due to the changes induced in the electrokinetic and physicochemical properties of the protein and membrane surfaces. Burns and Zydney [7] investigated the effect of solution pH on the transport of globular proteins with different surface charge characteristics through polyether sulfone (PES) membranes. The protein sieving coefficient attained its maximum value near the IEP, but decreased at pH values above and below the IEP, due to changes in the electrostatic interactions. The authors postulated th...

Effects of ionic environment on the interfacial interactions between α‐amylase and polyether sulphone membranes

“…At the IEP of amylase (pH = 5.6), the net charge of amylase is zero and hence, electrostatic interactions are minimal. At this point, adsorption might occur because the protein has a more hydrophobic and compact structure in the isoelectric region, and therefore, a smaller tendency to spread at the interface 1, 21. It is conceivable that adsorption can occur due to mainly hydrophobic interactions at the IEP of α‐amylase.…”

“…Before all experiments, the membranes were rinsed with Milli‐Q (Gradient model, Millipore) deionized water to remove preservatives. Hydrophobic PES membranes have negatively charged under the all experimental conditions 1, 10. Molecular weight of model enzyme α‐amylase (from Aspergillus oryzae , Fluka, 10 065) is 51–58 kDa and its IEP is pH = 5.6–5.8 18.…”

“…The main factors that influence fouling are the hydrodynamics of the separation process and the interfacial interactions between protein–membrane and protein–protein. Interactions between charged molecules and membrane surfaces may be classified into the following major contributions: electrostatic interaction between the protein and the surfaces, and hydrophobic dehydration of various parts of the protein molecules, structural rearrangements in the protein molecule and van der Waals interactions 1–3…”

Determination of correct zeta potential of polyether sulfone membranes using CLC and AGC: ionic environment effect

“…Although membrane processes have many advantages, such as low energy consumption, no phase changes, easy scale-up, the fundamental problem of industrial membrane processes when compared with classic separation techniques is membrane fouling [1][2][3]. In order to solve this problem, many researchers have used membrane zeta potential as a key parameter [4][5][6][7][8], because membrane and particle zeta potentials provide important information about the nature and magnitude of membrane fouling caused by the membrane-particle interfacial interactions. The correct value of zeta potential is significant for determining the direction of the next steps in the process.…”

Evaluation and comparison of protein ultrafiltration test results: Dead-end stirred cell compared with a cross-flow system

“…Several researchers have demonstrated the influence of ionic strength on permeate flux. Solution pH has been shown to have less of an effect at higher ionic strengths [6][7][8][9]. Whilst sufficient evidence exists in the literature to demonstrate the importance of electrostatic interactions [1,4,9,10] there still seem to be differing observations concerning permeate flux and rejection at and around the pI of the protein.…”