Membrane separation is an important processing technology used for separating food ingredients and fractionating value-added components from food processing byproducts. Long-term performance of polymeric membranes in food protein processing is impeded by the formation of fouled layers on the membrane surface as a result of protein adsorption onto the membrane surface. Surface modification of synthetic membranes, i.e., changing surface characteristics to reduce protein adsorption permanently, is one of the innovative ways of reducing the fouling of membrane surfaces. In this study, surface modification of flat-sheet ultrafiltration membrane, polyethersulfone (PES), was investigated in improving the hydrophilicity of PES surfaces, thereby reducing adsorption of the protein caused by hydrophobic-hydrophobic interaction between the protein and the membrane. Hydrophilic polymer grafting through thin-film composite using interfacial polymerization was employed to improve the hydrophilicity of the commercial PES membranes. Poly(vinyl alcohol), poly(ethylene glycol), and chitosan were chosen as hydrophilic polymers to graft on PES membrane because of their excellent hydrophilic property. Modified PES membranes were characterized by contact angle, FTIR, XPS, and AFM. Contact angles of modified PES membranes were reduced by 25 to 40% of that of the virgin PES membrane. XPS spectrum supported that the PES membranes were successfully modified by interfacial polymerization. Tapping-mode AFM was used to examine the changes in surface topography of modified PES membranes. The PES membranes modified by interfacial polymerization showed lower roughness (from 1.2 to 2.0 nm) than that of virgin PIES membrane (2.1 nm). The results of these instrumental analyses indicated that the PIES membranes were successfully enhanced hydrophilically through interfacial polymerization. The protein adsorption on the modified membranes was reduced by 30 to 35% as a result of surface modification of the PES membranes using interfacial polymerization technique. (C) 2009 Wiley Periodicals, Inc.* J Appl Polym Sci 112: 1704-1715, 2009