The continuous enzymatic production of difructose anhydride III (DFA III) from inulin as a substrate using ultrafiltration membrane bioreactor (UFMB) system was investigated. DFA III is a non-digestible oligosaccharide and has recently attracted interest as prebiotics. In the paper presented below, native inulin fructotransferase (IFTase) from Arthrobacter aurescens SK 8.001 was used as enzyme to catalyze transfructosylation reaction to produce DFA III, competed against the hydrolysis of inulin. When the substrate concentration is 100 g/L, the largest amount of difructose anhydride III (DFA III) was produced by 6-h hydrolysis of inulin. To optimize DFA III yield, process conditions were obtained: E/S 30 U/g, temperature 60-70 degrees C, pH 5.0-7.0, and 1-h hydrolysis time. Compared with the batch reactor, IFTase could be reused and the productivity and purity of DFA III could attain about 2379 and 92% in the UFMB. An operation stability study showed that the UFMB system could maintain the steady production of DFA III for over 12 h, and periodic addition of fresh inulin solution and IFTase could be added to the bioreactor. (C) 2011 Elsevier B.V. All rights reserved.