What Is Chitin? Definition and Uses

Chitin [(C₈H₁₃O₅N)_n] is a polymer consisting of N-acetylglucosamine subunits joined by covalent β-(1→4)-linkages. N-acetylglucosamine is a glucose derivative. Structurally, chitin is similar to the cellulose, which consists of glucose subunits and is also joined by β-(1→4)-linkages, except one hydroxyl group on a cellulose monomer is replaced by an acetyl amine group in a chitin monomer. Functionally, chitin most closely resembles the protein keratin, which is used as a structural component in many organisms. Chitin is the second most abundant biopolymer in the world, after cellulose.

The structure of chitin was described by Albert Hoffman in 1929. The word "chitin" derives from the French word chitine and Greek word chiton, which mean "covering." Although both words come from the same source, "chitin" should not be confused with "chiton," which is a mollusk with a protective shell.

A related molecule is chitosan, which is made by deacetylation of chitin. Chitin is insoluble in water, while chitosan is soluble.

Chitin Properties

Hydrogen bonding between monomers in chitin make it very strong. Pure chitin is translucent and flexible. However, in many animals, chitin is combined with other molecules to form a composite material. For example, in mollusks and crustaceans it combines with calcium carbonate to form hard and often colorful shells. In insects, chitin is often stacked into crystals that produce iridescent colors used for biomimicry, communication, and to attract mates.

Chitin Sources and Functions

Chitin is primarily a structural material in organisms. It is the main component of fungal cell walls. It forms the exoskeletons of insects and crustaceans. It forms the radulae (teeth) of mollusks and the beaks of cephalopods. Chitin also occurs in vertebrates. Fish scales and some amphibian scales contain chitin.

Health Effects in Plants

Plants have multiple immune receptors to chitin and its degradation products. When these receptors are activated in plants jasmonate hormones are released that initiate an immune response. This is one way plants defend themselves against insect pests. In agriculture, chitin may be used to boost plant defenses against disease and as a fertilizer.

Health Effects in Humans

Humans and other mammals do not produce chitin. However, they have an enzyme called chitinase that degrades it. Chitinase is present in human gastric juice, so chitin is digestible. Chitin and its degradation products are sensed in the skin, lungs, and digestive tract, initiating an immune response and potentially conferring protection against parasites. Allergies to dust mites and shellfish are often due to a chitin allergy.

Other Uses

Because they stimulate an immune response, chitin and chitosan may be used as vaccine adjuvants. Chitin may have applications in medicine as a component of bandages or for surgical thread. Chitin is used in paper manufacturing as a strengthener and sizing agent. Chitin is used as a food additive to improve flavor and as an emulsifier. It is sold as a supplement as an anti-inflammatory agent, to reduce cholesterol, support weight loss, and control blood pressure. Chitosan may be used to make biodegradable plastic.

Sources

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• Elieh Ali Komi, D.; Sharma, L.; Dela Cruz, C.S. (2017). "Chitin and Its Effects on Inflammatory and Immune Responses." Clinical Reviews in Allergy & Immunology. 54 (2): 213–223. doi:10.1007/s12016-017-8600-0
• Karrer, P.; Hofmann, A. (1929). "Polysaccharide XXXIX. Über den enzymatischen Abbau von Chitin and Chitosan I." Helvetica Chimica Acta. 12 (1) 616-637.
• Tang, W. Joyce; Fernandez, Javier; Sohn, Joel J.; Amemiya, Chris T. (2015) "Chitin is endogenously produced in vertebrate." Curr Biol. 25(7): 897–900. doi:10.1016/j.cub.2015.01.058