Ultrafiltration was investigated as possible alternative to ethanol precipitation for isolation of arabinoxylooligosaccharides (AXOS) with different structures from enzymically produced arabinoxylan (AX) hydrolysates. Incubation of wheat flour AX with an Aspergillus aculeatus endoxylanase yielded mixtures of AX poly- and oligosaccharides. Their fractionation by graded ethanol precipitation or ultrafiltration membranes with different molecular mass cut-off yielded fractions, which differed both in degree of polymerization (DP) and degree of substitution (DS). Although the ultrafiltration fractions were more heterogeneous than the ones obtained by ethanol precipitation, AXOS fractions with similar DP and DS could be obtained with both methods. (c) 2005 Elsevier Ltd. All rights reserved.