Method for preparing chitosan into water-soluble chitosan oligosaccharide

The invention relates to a method for preparing chitosan into water-soluble chitosan oligosaccharide. The method is as below: rinsing and drying a raw material chitosan, soaking chitosan into a feed liquid prepared from clean water and food grade hydrogen peroxide, conducting microwave radiation degradation treatment to form a mixed solution of low molecular chitosan oligosaccharide dissoluble in the feed liquid and non-degraded chitosan, then filtering to obtain by chitosan residue and a chitosan oligosaccharide solution, subjecting the chitosan oligosaccharide solution to alcohol precipitation in ethanol, and conducting suction filtration and drying to obtain the water-soluble chitosan oligosaccharide product. Due to the microwave radiation degradation treatment technology and physical method for lasing energy, polymer chitosan degrades into low molecular water- soluble chitosan oligosaccharide with stable structure; and in the degradation process, no other reaction by-products or pollutants are generated. Compared with the preparation method in the prior art, the method has the advantages of advanced technology, simple process, less investment in production facilities, high product purity and stable quality, and opens broad market prospect for chitosan prepared from chitin as raw material.