Purification method of nattokinase

The invention belongs to the technical field of compound purification, and relates to a method for purifying nattokinase, which comprises the following steps: carrying out enzymolysis on nattokinase fermentation liquor, and then purifying the obtained enzymatic hydrolysate, the enzymolysis method comprises the following steps: diluting the nattokinase fermentation liquor with water until the viscosity is 180-250mPa. S, and carrying out enzymolysis on the obtained nattokinase diluent with an enzyme preparation to obtain enzymatic hydrolysate, the enzyme preparation is selected from at least one of trypsin, papain, carboxypeptidase, polyglutamic acid polypeptidase and beta-lactamase, and the enzymatic hydrolysate is at least one of trypsin, papain, carboxypeptidase, polyglutamic acid polypeptidase and beta-lactamase. The addition amount of the enzyme preparation is 0.1%-5% of the volume of the nattokinase fermentation liquid, and the viscosity of the enzymatic hydrolysate is reduced to 100 mPa.s or below under