This paper investigates the feasibility of producing a soy milk fraction enriched in trypsin inhibitor (STI) which could serve as a feed material for chromatographic purification of STI. This STI is also a soy antinutritional factor which is valuable for its medical and scientific applications. We have used a shear-enhanced filtration system with a disk rotating at high speed near the membrane. Stabilized permeate fluxes at 2500 rpm, with a disk equipped with vanes and a transmembrane pressure (TMP) of 67 kPa were 92 L h(-1) m(-2) with a 50 kDa MWCO PES membrane against 60Lh(-1) m(-2) with a 300 kDa one, under the same conditions. STI rejection by the 50 kDa membrane was 98.6%. With a smooth disk at a TMP of 107 kPa, fluxes fell to 30 L h(-1) m(-2) for both membranes, and rejection remained close to 98% for the 50 kDa membrane. During concentration tests, the permeate flux obeyed the logarithmic decay with concentration factor (CF), with a theoretical maximum CF of 4.85. (c) 2006 Elsevier B.V. All rights reserved.