The present disclosure relates to methods for producing human milk oligosaccharide (HMO) core structures using glycosidases from family GH20 hexosaminidases. In particular, the present disclosure provides methods for producing lacto-N-triose II (LNT II) and/or lacto-N-tetraose (LNT) by reacting glucosamine-oxazoline and/or lacto-N-biose-oxazoline with lactose catalysed by an enzyme of the glycoside hydrolase family 20 (GH20) according to the classification of the Carbohydrate-Active-Enzymes (CAZy) database. Specific optimized enzymes are identified to catalyse the reactions.

A method for synthesizing lacto-N-biose and belongs to the technical field of bioengineering and oligosaccharide synthesis. A multi-enzyme catalytic system with good biological safety and wide application, and an ATP regeneration cycle system is introduced into a multi-enzyme reaction system, so that the synthesis of lacto-N-biose and the utilization rate of substrates are improved. A novel lacto-N-biose synthetic route lays a foundation for large-scale industrial production of lacto-N-biose and has important economic values and social benefits. At the same time, the synthetic method is efficient, mild, simple, easy to operate, low in cost and suitable for industrial production, and has a high practical application value.