Method for preparing chitosan through composite fermentation

The invention discloses a method for preparing chitosan through composite fermentation. The method comprises the following steps: drying crab shell or shrimp shell, and crushing; fermenting; removing calcium; removing proteins; and carrying out enzymatic hydrolysis for acetyl removal, washing with water, drying, and crushing. Compared with the prior art, the above enzymatic hydrolysis method has the advantages of reduction of the consumption of a strong acid, low energy consumption, no pollution and environmental protection. A fermentation liquid can be recovered to prepare biological osteocalcin, so all products can be reasonably utilized to generate substantial economic values and avoid resource waste.