Electrofiltration (EF) was used to selectively separate cationic (basic) peptides contained in a tryptic beta-lactoglobulin (beta-LG) hydrolysate, with particular emphasis on the isolation of basic sequence beta-LG 142-148, which is a potential anti hypertensive peptide. Both the influence of feed solution pH and operating parameters (transmembrane pressure, feed velocity) were assessed to find optimum conditions enabling the fractionation between peptides during EF. The cathode (-) was inserted in the permeate side to increase the separation of basic peptides contained in the tryptic beta-LG hydrolysate as compared to conventional NF. The highest separation factor between basic and neutral peptides was obtained at pH 9 using G-10 membrane with a molecular weight cut-off (MWCO) of 2,500 g/mol, at 5 V with the lowest transmembrane pressure (0.344 MPa) and feed velocity (0.047 m/s). The transmission behavior of the peptides during EF was better explained when taking into account the positive/negative charge ratio. Because of its 3+/1- charge ratio, beta-LG 142-148 had the highest transmission during EF. Consequently, its relative concentration was raised from 3.5% in the initial tryptic beta-LG hydrolysate up to 38% in the permeate. The electric field seemed more effective when the convective/shearing forces were minimized. (c) 2006 Wiley Periodicals, Inc.