The present work considers the influence of surfactants and coagulant on the ultrafiltration (UF) of whey suspensions in ceramic membranes. The filtration performance is assessed both in terms of permeate flux and total organic carbon (TOC). Prior to filtration, the stability of whey suspensions under different conditions was characterized in terms of particle sizes and zeta potentials. Additionally, the membrane was characterized in terms of its zeta potential (zeta). A higher range of permeate flux was found at pH 6.2 when both particles and membrane had significant zeta-potentials. In contrast better TOC reductions were observed at pH 3.0 when the zeta-potentials of both membranes and particles were low. Generally, larger average particle sizes were obtained at pH 3.0 where the zeta-potentials of the particles were lower which encouraged aggregation. However, the presence of these larger particles did not seem to improve the filtration performance. This study demonstrates that electrokinetics can exert more influence than particle size on membrane performance. (C) 2009 Elsevier B.V. All rights reserved.