Fractionation of polysaccharides from rapeseed by ultrafiltration: Effect of molecular pore size and operation conditions on the membrane performance

This paper describes a detailed investigation of ultrafiltration of polysaccharides from rapeseed. Four different commercial membranes made of polyvinylidene fluoride kynoar (PVDF) and polyether sulfone were used. During the preliminary treatment, rapeseed was in turn crushed, dehulled, defatted, homogenized and deproteinized. And then the resulting solution was subjected to ultrafiltration (UF) using three different molecular weight cut-off membranes (3, 8 and 12 kDa). The factors, namely, transmembrane pressure and solution conditions (pH, ionic content and temperature), that affected permeate fluxes were optimized. The results showed that transmembrane pressures, feed pH and temperature influenced permeate fluxes greatly, but ionic content hardly had any positive effect. Furthermore, the effects of ultrafiltration were evaluated in terms of recovery and purity of resulting polysaccharides. The results showed that the membrane of 3 kDa MWCO ensured not only the highest recovery of polysaccharides, but also high purity, compared to the two others. Finally, the rejected polysaccharides were also characterized in terms of molecular weight distribution (MWD) by size exclusion chromatography in HPLC. The findings thus clearly suggest purification of polysaccharides from rapeseed by the membrane of 3 kDa MWCO is feasible with high recovery and purity. (C) 2011 Elsevier B.V. All rights reserved.