Impact of water splitting phenomenon during electrodialysis with ultrafiltration membranes on peptide selectivity and migration Alain Doyen a,b , Cyril Roblet a,b , Lucie Beaulieu a,c , Linda Saucier a,d , Yves Pouliot a,b , Laurent Bazinet a,b,n a Institute of Nutraceuticals and Functional Foods (INAF), Universite´ Laval, Que ´bec, QC, Canada G1V 0A6 b Department of Food Science and Nutrition, Universite´ Laval, Que´bec, QC, Canada G1V 0A6 c Department of Biology, Chemistry and Geography, Universite´ du Que ´bec  a Rimouski (UQAR), Rimouski, QC, Canada G5L 3A1 d Department of Animal Science, Universite´ Laval, Que ´bec, QC, Canada G1V 0A6 article info Article history: Received 30 July 2012 Received in revised form 12 October 2012 Accepted 21 October 2012 Available online 31 October 2012 Keywords: Snow crab by-products hydrolysate Potential differences Ion-exchange membrane Limiting current density Ultrafiltration membrane abstract The effect of applying different electric field strength values during electrodialysis with ultrafiltration membranes (EDUF) was studied to optimize the EDUF process, in terms of peptide migration and selectivity, and to understand the impact of the electric field on membrane electrical and physical behavior. The electrical potential differences of two ultrafiltration membranes (UFM), one anion- exchange membrane (AEM) and two cation-exchange membranes (CEM) were measured in situ during EDUF fractionation. Permeate samples (KCl) were recovered for the determination of peptide migration rate from snow crab by-products hydrolysate. As expected, the peptide concentration in the KCl permeates increased during separation, when the electric field increased. However, the migration of low molecular weight peptides (LMWPs) was more important than high molecular weight peptides (HMWPs). It was shown that only the AEM was affected by electric field strength higher or equal to 3.6 V/cm. This value corresponds to the appearance of a limiting current density (LCD). Finally, during EDUF separation, when limiting current density (LCD) was reached, no variation in peptide selectivity was observed whereas a plateau was reached contrary to peptide migration rate which continually increased during EDUF separation. & 2012 Elsevier B.V. All rights reserved. 1. Introduction During electrodialytic processes, the current within the mem- brane is principally carried by the counter ions due to the exclusion of co-ions. Consequently, concentration gradients are formed in the boundary layers adjacent to the membrane [1]. Thus, the ion concentration on the diluate side decreases whereas it increases on the concentrate side of the ion-exchange mem- brane [1]. When the ion concentration on the diluate side is close to zero, the limiting current density is then reached [1,2]. If the limiting current density is exceeded, water molecules are dis- sociated into H þ and OH  and consequently changes in the pH of the solutions occur [3–5]. Simons [3–6] found that water dissociation appeared generally at the interface of anion-exchange membrane and originates from carboxylic acid, phenolic and primary, secondary and tertiary alkyl amino groups. Water splitting phenomenon is probably due to protonation and deprotonation reactions involving the functional groups at the membrane surface facing the diluate solution. More recently, Rubinstein et al. explained the appearance of limiting current density and water splitting at anion- and cation-exchange membrane interfaces by electroconvec- tion mechanism [7,8]. Electroconvection occurs due to the action of the electric field on the electric space charge in the boundary depleted solution [9,10]. This phenomenon explained particularly the appearance of water splitting at cation-exchange membrane interface [11]. Electrodialysis with ultrafiltration membrane (EDUF) is a technology patented in 2005 by Bazinet et al. [12] and allowing the migration of molecules according to their charges and molecular weights. The EDUF configuration consists of ultrafiltra- tion (UFM) and ion-exchange membranes (IEM) stacked in a conventional electrodialysis cell. EDUF cell was generally com- posed of a feed solution compartment corresponding to the solution to be separated and two recovery compartments for anionic and cationic peptides which contain a salt solution (KCl) for electrical current circulation. This technology has been found Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/memsci Journal of Membrane Science 0376-7388/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.memsci.2012.10.036 Abbreviations: AEM, anion-exchange membrane; BCA, bicinchoninic acid; BSA, bovine serum albumin; CEM, cation-exchange membrane; ED, electrodialysis; EDUF, electrodialysis with ultrafiltration membranes; HMWP, high molecular weight peptide; IEM, ion-exchange membrane; LCD, limiting current density; LMWP, low molecular weight peptide; MWCO, molecular weight cut-off; UFM, ultrafiltration membrane n Corresponding author at: Universite ´ Laval, Department of Food Science and Nutrition, Pavillon Comtois, Local 1403 Quebec, Canada G1V 0A6. Tel.: þ1 418 656 2131; fax: þ1 418 656 3353. E-mail address: laurent.bazinet@fsaa.ulaval.ca (L. Bazinet). Journal of Membrane Science 428 (2013) 349–356