Newly developed parallel small-scale enzymatic membrane reactors (EMRs) were used to enhance the synthesis of lactulose using beta-galactosidase. Under batch operation, the productivity of lactulose decreased abruptly from 2.72 down to 0.04 mg(lactulose)/(U(enzyme)h) over 35 h of reaction. This was presumably caused by the action of beta-galactosidase which performed secondary hydrolysis upon the produced lactulose. The continuous operations of an EMR system led to continuous removal of lactulose in the reactors restricting lactulose degradation caused by secondary hydrolysis. Therefore, continuous lactulose syntheses in the EMRs yielded significantly higher specific productivities under "steady state'' conditions. Approximately 0.70 and 0.50 mg(lactulose)/(U(enzyme)h) for hydraulic residence times of 5 and 7 h were reached, respectively. Continuous lactulose synthesis performed in an EMR system conclusively can circumvent the drawbacks (e. g., secondary hydrolysis) of lactulose synthesis encountered in batch operation. It is, therefore, beneficial in terms of enhanced lactulose productivity and reduced enzyme consumption. (C) 2014 Elsevier Ltd. All rights reserved.