Lactulose production is a complex process that is affected by several operational and experimental conditions. This study investigated the production of prebiotic lactulose using an electro-activation reactor. The experiments were performed at an ambient temperature (22 +/- 1 degrees C), and the lactose starting concentration was constantly maintained at 5% (w/v). This work used HPLC to investigate the retention behaviors of the disaccharides (lactulose and lactose) and the by-products of lactulose production (glucose, galactose and fructose) under varying experimental conditions such as electric potential difference, central cell compartment electrolyte concentration and electro-activation time. The results were then correlated with the electric current density, the electrical global resistance of the system, the pH, the temperature and the Joule heating effect. The highest lactulose yield that was obtained during the isomerization of lactose was approximate to 30% at a voltage of U = 28 V, an electrolyte concentration C-Na2SO4 = 0.5 M, a temperature T = 26 degrees C, an alkaline medium pH = 10.79, and a running time tau = 20 min. (c) 2013 Elsevier Ltd. All rights reserved.