The effects of externally applied electric field during cross-flow ultrafiltration of synthetic juice (mixture of sucrose and pectin) are studied and the gel thicknesses are measured optically. The introduction of the electric field is found to be quite effective in enhancing the permeate flux due to the electrophoresis of the gel forming pectin molecules away from the membrane surface. A model based on gel layer theory is proposed and numerically solved to quantify the flux and growth of the gel layer thickness. The gel layer thickness is also measured with high-resolution video microscopy and successfully compared with results from the numerical solution of the model under various operating conditions. (C) 2007 Elsevier B.V. All rights reserved.