Chitin: Structure, Function, and Uses

The hard outer shell of arthropods and insects like beetles is primarily made up of chitin, a naturally occurring biopolymer. The following BiologyWise article elaborates more on the structure, function, and uses of chitin.

BiologyWise Staff

Did You Know?

Behind cellulose, chitin is the second-most abundant natural biopolymer in the world.

If one is to observe a lobster closely, he cannot fail to notice its tough outer covering. This protective outer shell, referred to as the exoskeleton is a distinguishing feature of arthropods that include crustaceans (crabs, lobsters, shrimp), arachnids (ticks, mites, scorpions, and spiders), and even insects (beetles, grasshoppers, butterflies). Chitin, a naturally occurring biopolymer is an important component of this exoskeleton. The internal shells of cephalopods and radulae of mollusks are also primarily composed of chitin.

Structure

Chitin is essentially a linear homopolysaccharide (long chain polymer) consisting of repeated units of N-acetyl-glucosamine, which is a monosaccharide derivative of glucose. These units form covalent β-1,4 linkages. Chitin with the chemical formula (C₈H₁₃O₅N)_n is considered as a complex carbohydrate, whose structure resembles that of cellulose, with one hydroxyl group on each monomer replaced with an acetyl amine group.

Chitin Structure

Function

This skeleton on the outside of the body appears hard and rigid due to the presence of chitin that is known for its tough elastic properties. Although chitin is the dominant constituent, other compounds such as proteins and calcium carbonate also play a crucial role in the formation of exoskeleton. The main function of this chitin-containing exoskeleton is to keep the inner soft tissue safe from any sort of injury.
Most importantly, it prevents these delicate tissues from becoming dry. In short, it acts as a watertight barrier against dehydration, which is crucial for their survival.
The hard chitin-containing exoskeleton of arthropods also acts as a defense mechanism against predation. This outer covering can tolerate strong compressive stresses, which can provide protection from predation because predators exert a compressive force on the exoskeleton to injure their victim.
The fungal cell wall that protects the micro-organism from the outside environment is also made up of chitin.

Exoskeleton Shedding

Chitin is released from the animal's outer skin (epidermis) to form the protective covering. After the exoskeleton fully develops, the growth of epidermis stops. Moreover, the exoskeleton is found to be relatively rigid, since it does limit growth with the increase in the size of the animal. So when there is a mismatch between the anatomy of the arthropod and the size of the exoskeleton, it can cause suffocation. To avoid this, the animal gets rid of the exoskeleton and begins to form a new one. This process of shedding the current skeleton is done periodically, which is necessary for their proper growth.

Uses

As a Fertilizer

One of the most important benefits of chitin is its use in making fertilizers. Chitin-containing fertilizers are organic, non-toxic, and have shown to increase crop productivity. Chitin in fertilizers helps in increasing soil organisms and enzyme activities, which positively affects soil health. This in turn increases crop yield.

As a Food Additive

Chitin has a long history of use as a food additive. It is commonly obtained from crabs, and shellfish that include shrimp. Sometimes cell walls of eumycetes (a type of fungi) are used as a source for extracting chitin. Microcrystalline chitin (MCC) as a food additive can be helpful to enhance taste and flavor.

As an Emulsifying Agent

Use of food chitin can also help in creating stable food emulsions. It essentially acts as an excellent emulsifying agent, which helps to prevent the breaking of emulsion when exposed to other fluids. For instance, whipped dessert toppings often contain chitin that provides uniformity and stability to the product.

Medicinal Uses

This naturally-occurring fiber-forming polymer can also help to lower cholesterol levels as found out through animal studies. Chitin molecules tend to mop cholesterol and fat in the digestive system. So chitin in the diet may help to reduce cholesterol absorption efficiency.

As a Surgical Thread

Chitin is also used for manufacturing strong and flexible surgical threads. Quite a few dissolvable stitches used to close wounds are made from chitin. These stitches start decomposing during the wound healing process. Reports also suggest that stitches composed of chitin may help to facilitate the healing of wounds.

Chitin in its supplemental form may help to reduce cholesterol. Moreover, chitin is said to have antioxidant, anti-diabetic, anti-inflammatory, antimicrobial, anticoagulant, antihypertensive, and anticancer properties. So taking it in the supplemental form may be beneficial for overall health.