Chemical Composition and Structure of Chitin

Chitin is a long-chain polymer of N-acetylglucosamine, a derivative of glucose. It is a fibrous structural heteropolysaccharide composed of N-acetyl-D-glucosamine units and chemically classed as an aminopolysaccharide. The monomer units are joined together by glycosidic bonds to form a linear backbone. The molecular structure of chitin is very similar to that of cellulose, with repeated acetamide (-NHCOCH3) groups replacing the hydroxyl groups of cellulose. This makes chitin slightly softer than pure cellulose. The strong polymer chains run in a longitudinal direction and are arranged in microfibrils. Within the microfibrils, the polymer chains are tightly packed and held together by hydrogen bonds for mechanical strength.

Natural Occurrence and Sources of Chitin

Chitin is one of the most abundant renewable biopolymers found in nature. It is estimated that more chitin is synthesized every year than cellulose. It is produced naturally by various organisms including fungi, yeasts, insects, molluscs and crustaceans. The primary commercial sources of chitin are from marine byproducts of the fishing industry, mainly from shells of shrimps, crabs and lobsters. The shells of krill also contain high amounts of chitin. Fungal cell walls contain about 30–40% of chitin as a major component. Chitin is also found to a minor extent in insect exoskeletons and mollusc shells. It represents a major reserve of bio-polymer that remains relatively unexploited.

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