Immobilizing enzymes such as β-galactosidase, peptidase and dextranase on membranes featuring adequate MWCO, is also a practical tool to intensify the production of value-added compounds with tailored molecular weight via size-exclusion operations. For example, the production of galactooligosaccharides (GOS) from lactose is hindered by hydrolytic side reactions, and by enzyme inhibition caused by such monosaccharides formation and accumulation. To improve reaction yield and productivity, the continuous coupled GOS purification and monosaccharides elimination from the reaction mixture is of particular interest. To this aim, ultrafiltration membranes are employed to simultaneously host the enzymes and perform the product separation . However, considering the molecular weight distribution of the carbohydrate mixture obtained after enzymatic reaction with lactose, nanofiltration also appears as an effective operation for GOS purification. Bhattacharjee et al.