In this study, the retention behaviours of disaccharides (lactulose and lactose) and catalysts (NaCl and H(3)BO(3)) in the prepared lactulose syrup were investigated in a pilot scale test of nanofiltration. Their retentions in the syrup by the applied membrane, ranked from high to low, were: disaccharides (94.7-98.5%) > NaCl (9.0-20.0%) > H(3)BO(3) (-19.9-0.0%). These differences in retention were significant, which made it possible to carry out their separation in syrup. In addition, a model was utilized to simulate the purity and yield of disaccharide during the continuous diafiltration process. According to the simulation, 25.0 bar was chosen as the optimum operating pressure for a continuous diafiltration process. Based on the experimental results, it was found that more than 96.5% of NaCl and H(3)BO(3) were removed from lactulose syrup with only a small loss (11.0%) of disaccharides when the V(c)/V(f) (multiple of dilution) was 5.0 for the membrane used. (C) 2011 Elsevier Ltd. All rights reserved.