Journal of Membrane Science 222 2003 41–51
Fouling with protein mixtures in microfiltration: BSA–lysozyme and BSA–pepsin
L. Palacio
a
, C.-C. Ho
b
, P. Prádanos
a
, A. Hernández
a ,
∗
, A.L. Zydney
c
a
Department of Thermodynamics and Applied Physics, University of Valladolid, Valladolid E-47071, Spain
b
Department of Chemical Engineering, University of Cincinnati, Cincinnati, OH 45221, USA
c
Department of Chemical Engineering, The Pennsylvania State University, University Park, PA 16802-4400, USA Received 16 May 2002; received in revised form 13 February 2003; accepted 14 February 2003
Abstract
Protein fouling during microfiltration has been investigated for mixtures of bovine serum albumin BSA and lysozyme and of BSA and pepsin. Flux decay curves were analyzed using a recently developed model that accounts for simultaneous pore
blockage and cake formation. The model is in good agreement with the data and can be used to evaluate the effect of mixture composition on the concentration of protein aggregates and the properties of the protein deposit. For pepsin–BSA mixtures,
the initial fouling appears to be dominated by the BSA, whereas the rate of cake growth occurs primarily by the pepsin. This behavior is consistent with the large concentration of pepsin aggregates and the electrostatic repulsive interactions between
the negatively-charged BSA and pepsin. The behavior is more complex for mixtures of BSA and lysozyme. In this case, the fouling is dominated by the lysozyme, although mixtures with small amounts of added BSA foul more slowly than observed
with either of the pure proteins. © 2003 Published by Elsevier Science B.V.
Keywords: BSA; Pepsin; Lysozyme; Protein mixtures fouling; Microfiltration
1. Introduction
Fouling is a major limitation to the widespread use of membrane filtration
[1] . A lot of studies have been
made in order to avoid or control this problem. The fouling phenomenon is usually assumed to be due
to adsorption or deposition on the membrane surface or within the membrane pores. While the term foul-
ing is used in practice when referring to process and engineering deposits, the term adsorption, as defined
by IUPAC committee
[2] , means “enhancement or
∗
Corresponding author. Tel.: +34-983-423134; fax: +34-983-423136.
E-mail address: membranatermo.uva.es A. Hern´andez.
depletion of one or more components in an interfacial layer”.
Ultrafiltration is used for protein concentration, buffer exchange, and clarification of solutions con-
taining low molecular weight products. Protein foul- ing in ultrafiltration generally occurs on the external
membrane surface since most proteins are too large to pass through the pores of the ultrafiltration mem-
branes
[3–5] .
Microfiltration is a pressure-driven membrane pro- cess used for a wide range of separations in the
biotechnology, food, beverage, and dairy industry, among others. Membrane fouling during microfiltra-
tion can lead to more than an order of magnitude re- duction in the filtrate flux, even during the filtration of
relatively clean protein solutions
[6,7] . Recent work
0376-7388 – see front matter © 2003 Published by Elsevier Science B.V. doi:10.1016S0376-73880300143-1
42 L. Palacio et al. Journal of Membrane Science 222 2003 41–51
has demonstrated that this fouling is typically caused by the deposition of large protein aggregates on the
membrane surface [7–9]
. However, fundamental stud- ies of membrane fouling have almost always been
limited to solutions of a single protein. These results are very difficult to apply to the microfiltration of
many food products e.g. whey, beverages e.g. beer and wine, and bioprocessing solutions e.g. harvested
cell culture fluid, all of which contain a complex mixture of a wide range of protein molecules.
Güell and Davis [10]
have performed one of the only fundamental studies of fouling during microfil-
tration of protein mixtures. Flux decline data were ob- tained with bovine serum albumin BSA, lysozyme,
and ovalbumin, both alone and in binary and ternary mixtures. Fouling by BSA or lysozyme alone was
dominated by pore blockage internal fouling, while ovalbumin showed a transition between pore blockage
and cake filtration. Ovalbumin showed the greatest flux decline, which was attributed to the greater number
of large aggregates of this protein present in solution. Protein mixtures containing ovalbumin showed a flux
decline similar to that obtained with ovalbumin alone, suggesting that the ovalbumin aggregates dominated
the fouling behavior. The flux decline with mixtures of BSA and lysozyme was mid-way between the fouling
seen with the individual proteins. In contrast, the flux decline for mixtures of ovalbumin and lysozyme was
greater than that observed with either of the pure pro- teins. No quantitative analysis was provided for any
of these observations.
Ho and Zydney [11]
, have recently developed a combined pore blockage and cake filtration model for
protein fouling. This model was shown to provide an excellent fit of flux decline data for bovine serum
albumin [11]
and for a series of four other model proteins
[12] . The objective of this work is to study
the fouling behavior of several well-defined protein mixtures, using this combined pore blockage—cake
filtration model to obtain fundamental insights into the nature of the protein—protein interactions and
their effect on membrane fouling.
2. Theory
