The objective of this work is to obtain a relative separation of beta-lactoglobulin (beta-LG) from whey protein concentrate by fractionation of protein using two-stage ultrafiltrafion (UF) with 30 and 10 kg mol(-1) molecular weight cut-off (MWCO) flat-disk membranes in stirred rotating disk module followed by ion-exchange membrane chromatography (IEMC) using Vivapure (TM) Q Mini-H column. Prior to UF, centrifugation, microfiltration and a four-stage discontinuous diafiltration (DD) were carried out to obtain whey protein concentrate from raw casein whey. Centrifugation and microfiltration were carried out to remove the major foulants like colloidal matters, suspended casein particles and lipid. DD using 5 kg mol(-1) polyethersulphone (PES) membrane with volume concentration ratio (VCR) 2 in each stage was employed with an objective to enrich the whey proteins by removing most of lactose, minerals and salts. The effects of various parameters, like solution pH, trans-membrane pressure (TMP), stirrer speed and membrane rotation speed on UF flux and rejection were studied thoroughly. A 36% higher flux was obtained with a feed pH of 2.8 compared to that at pH of 5.6 at a fixed TMP of 5.0 X 10(5) Pa which has been explained with the help of the effect of pH on monomer-dimer equilibrium of beta-LG and prevailing protein charge. A 33% enhancement of flux was observed at 1 min with membrane disc rotating at 300 rpm compared to the corresponding value of stationary membrane due to reduction in concentration polarization, the main limiting phenomenon for flux decline. A suitable loading buffer pH was investigated during IEMC runs so as to get a facilitated transport of beta-LG over alpha-LA through the strong anion exchanger membrane. An 87.6% purity of beta-LG (on total protein basis) was obtained in the filtrate of ion-exchange membrane chromatography. (c) 2005 Elsevier B.V. All rights reserved.