Hemicelluloses of Pinus pinaster wood were selectively separated from cellulose and lignin by reaction with hot, compressed water (autohydrolysis) under optimized conditions. The reaction liquor contained polymeric or oligomeric hemicellulose saccharides (POHS, accounting jointly for 69.6% of the dissolved wood fraction), followed by monosaccharides (accounting for 20.0% of the non-volatile compounds), and non-saccharide compounds. For concentration, purification and fractionation purposes, liquors from hydrothermal processing were subjected to consecutive steps of diafiltration and concentration using membranes of 10, 5, 3, 1 and 0.3 kDa molar mass cut-off. Samples from selected process streams were characterized by chromatographic and spectrometric methods. The experimental results provided information on the separation and refining effects achieved by the various membrane processing steps, which affect the technological properties of products. (C) 2012 Elsevier B.V. All rights reserved.