P-Lactoglobulin tryptic hydrolysates contain numerous bioactive pepticles of which beta-lg 142-148 has been reported to be the most potent antihypertensive sequence. However, this peptide has to be isolated to obtain an ingredient with higher functionality. Electrodialysis with ultrafiltration membrane, a technique developed recently, has proven to be a selective way of fractionating peptides. The main goal of this work was to increase the productivity of this process by studying the influence of the effective membrane surface, by stacking ultrafiltration (UF) membranes, and the strength of the electrical field. Two different surfaces (10 and 40 cm 2) and three electrical field strengths (2.75, 5.5 and 11 V/cm) have been tested. The increase of the membrane area, by stacking four UF membranes, resulted in a four-fold increase of the peptide concentration and that independently of the voltage value. Moreover, raising the electrical field strength also resulted in increasing considerably the peptide concentration in the permeate solution. However, at high electrical field and membrane area, the final migration rate was affected due to a retro-migration phenomenon linked with pH changes. In the best conditions, a total migration of 29% was obtained for peptide beta-lg 142-148 after only 90 min of processing with a relative concentration of 30%. This paper describes the first study that demonstrates that one can successfully stack ultrafiltration membranes in an electrodialysis cell to significantly enhance the overall performance characteristics of the separation. (c) 2007 Elsevier B.V. All rights reserved.