How to make chitin, chitosan, and chitosan oligosaccharides?

Chitin and chitosan are extracted from crab and shrimp shells, but these shells are composed of proteins, fats (pigment), carbohydrates (chitin), and inorganic substances such as calcium carbonate. To produce chitin from crab shells, calcium carbonate (CaCO₃), which is an inorganic component, must be removed first. CaCO₃ can be removed using hydrochloric acid and the principle for this process is as follows: Calcium carbonate, which is also called limestone, generates calcium chloride (CaCl₂) and carbonic acid (H₂CO₃) when treated with acids such as hydrochloric acid. The calcium chloride is then dissolved in water and the carbonic acid is degraded into water and carbon dioxide (CO₂). After removing calcium carbonate, the residue is immersed in a dilute solution of sodium hydroxide (NaOH). Proteins and pigments are degraded and chitin is obtained after the products of degradation are removed.