Method for extracting collagen polypeptide and hydroxyapatite in fish scales by cooking hot extrusion

The invention relates to a method for extracting collagen polypeptide and hydroxyapatite in fish scales by cooking hot extrusion, which comprises the following steps: (a) pulverizing clean fish scales by a pulverizer; (b) putting the pulverized fish scales and water into a feed inlet of a double-screw cooking heat extruder for hot extrusion for 0.5-1h under the action of steam pressure to obtain thick slurry, wherein the content of the fish scales is 90%-95%; (c) after the treatment of the step b, adding water of which the weight is 8-10 times of the weight of the thick slurry, extracting collagen by water immersion, and filtering residues; (d) adding enzymes of which the weight is 1%-3% of the weight of the fish scales into the water solution of the collagen extracted in the step c for enzymolysis for 2-3h at 45-60 DEG C, heating to 90 DEG C after enzymolysis, keeping for 10min, and then inactivating the enzymes; (e) decoloring the enzymolysis solution obtained in the step d, removing impurities with an ultrafiltration membrane, concentrating the solution with a nanofiltration membrane, and freeze-drying the solution to obtain the collagen polypeptide of the fish scales; and (f) drying and pulverizing the residues obtained in the step c, and then, putting the residues in a muffle furnace for calcining for 1-2h at 700-1000 DEG C to obtain nano-hydroxyapatite. The invention does not need acid-base pretreatment, has good separation and purification effects and can not influence the activity of the collagen polypeptide and the hydroxyapatite in the fish scales.