Cellobiose 2-epimerase from Caldicellulosiruptor saccharolyticus was used in the presence of borate to increase the production of lactulose from lactose. Maximum production of lactulose occurred using a 1:1 M ratio of borate-lactose. Under this condition, the enzyme produced 614 g l(-1) lactulose from 700 g l(-1) lactose after incubation at pH 7.5 and 80 degrees C for 3 h, with a conversion yield of 88% and a productivity of 205 g l(-1) h(-1). The yield and productivity of lactulose production obtained in the present study are among the highest achieved through chemical or biological synthesis. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.