Method for preparing lactulose and co-producing galactooligosaccharide

The invention relates to a method for preparing lactulose and co-producing galactooligosaccharide, and belongs to the technical field of functional sugar preparation.The method comprises the steps that lactose serves as a raw material and is converted into lactulose under the high-temperature alkaline condition, beta-galactosidase is added, unreacted lactose and a lactose solution are converted into galactooligosaccharide, and the galactooligosaccharide is obtained; the problem that unreacted lactose is easy to crystallize in the lactulose preparation process is solved, meanwhile, the problem that lactulose obtained by adopting a chromatographic separation purification process after lactose secondary crystallization is low in purity is solved, and the purity of the obtained lactulose reaches 95% or above. The method has the advantages that basic catalysts such as borate or aluminate do not need to be added, the refining process is simple and easy to implement, the calcium resin is firstly adopted for primary