This study discusses the impact of biopolymer purification - by dialysis and by dia-ultrafiltration - on the properties and transport performance of composite polysaccharide membranes for pervaporation. The composite membranes prepared, using as active layer polysaccharides purified by these two methods, were compared in terms of structure, resistance to solvents, mechanical and transport properties. Both composite membranes exhibited identical resistance to organic solvents, but presented significant differences in terms of swelling degree and transport selectivity. It was found that these differences may be caused by the shear stress imposed during purification by the dia-ultrafiltration method, which leads to a disintegration of polysaccharide aggregates. As a consequence denser membranes are obtained, clue to smaller polysaccharide aggregates formed, which impact the transport selectivity. Membranes prepared with polysaccharides purified by dia-ultrafiltration revealed to be the best choice for ethanol dehydration by pervaporation, since a water/ethanol selectivity of 143 for 10.0 wt% water in ethanol was achieved. (C) 2015 Elsevier B.V. All rights reserved.