Synthesis of galactooligosaccharides by CBD fusion β-galactosidase immobilized on cellulose

► The fusion of Lactobacillus bulgaricus β-galactosidase with cellulose binding domain. ► The immobilization of the fusion enzyme on cellulose. ► The maximal galactooligosaccharides yield by the cellulose immobilized enzyme reached 49%. ► The immobilized enzyme could be recycled for 20 batches with oligosaccharide yields all above 40%.