Lactulose production from lactose as a single substrate by a thermostable cellobiose 2-epimerase from Caldicellulosiruptor saccharolyticus

The conditions for maximum lactulose production from lactose, as a single substrate, by a thermostable recombinant cellobiose-2-epimerase from Caldicellulosiruptor saccharolyticus were determined to be pH 7.5, 80 °C, 700 g l−1 lactose, and 150 U ml−1 of enzyme. Under the conditions, the enzyme produced the two bifidus factors lactulose at 408 g l−1 and epilactose at 107 g l−1 after 2 h. The yields of lactulose and epilactose from lactose and the productivities of lactulose and epilactose were 58%, 15%, 204 g l−1 h−1, and 54 g l−1 h−1, respectively. The yield and productivity of both lactulose and epilactose from lactose were 74% and 258 g l−1 h−1, respectively. The yield, concentration, and productivity of lactulose in the present study are the highest among enzymatic syntheses. This is the first trial of enzymatic synthesis of lactulose using the single substrate lactose.