Chitin and Chitosan

Chitin and Chitosan

What is Chitin?

Chitin is the second most abundant naturally occurring biopolymer 

(after cellulose) and is found in the exoskeleton of crustaceans, in 

fungal cell walls and other biological materials. It is mainly poly (ß-(1-

4)-2-acetamide- D-glucose), which is structurally identical to cellulose 

except that secondary hydroxyl on the second carbon atom of the 

hexose repeat unit is replaced by an acetamide group

• What is chitosan?

Chitosan is a natural polysaccharide comprising copolymers of 

glucosamine and N-acetylglucosamine, and can be obtained by the 

partial deacetylation of chitin, from crustacean shells, the second most 

abundant natural polymer after cellulose. Chitosan is derived from 

chitin by deacetylation in the presence of alkali. Therefore, chitosan is 

a co-polymer consisting of (ß-(1-4)-2-acetamido-Dglucose and (ß-(1-

4)-2-acetamide-D-glucose units with the latter usually exceeding 80%

11.2. Characteristics of chitin and chitosan

• Chitin is a white, hard, inelastic, nitrogenous polysaccharide and the major 

source of surface pollution in coastal areas

• Chitosan is a fiber-like substance derived from chitin

• Chitin is the fiber in shellfish shell such as crab, lobster and shrimp

• The chitin is deproteinized, demineralized and de-acetylated. It is a dietary fiber, 

meaning that it cannot be digested by the digestive enzymes of a person

11.3. Preparation of Chitin and Chitosan

What are all the sources of Chitin?

It is also found in common foods we eat such as grain, yeast, bananas, and 

mushrooms. Like cellulose, it functions as structural polysaccharides. Its natural 

production is inexhaustible; arthropods, by themselves, count more than 106 species 

from the 1.2 X 106 of total species compiled for animal kingdom, constitute 

permanent and large biomass source.

How are chitin and chitosan prepared?

Chitin can be converted into chitosan by enzymatic means or alkali deacetylation, 

this being the most utilized method. During the course of deacetylation, part of 

polymer N-acetyl links are broken with the formation of D-glucosamine units, which 

contain a free amine group, increasing the polymer’s solubility in aqueous means.

Preparation of Chitin

The production of chitin from shrimp and crab waste involves two steps:

• Deproteinization

• Demineralization

• Demineralization is achieved using mineral acid and deproteinization of 

demineralized mass is achieved using dilute solution of caustic soda. Shell 

waste is stirred with dilute HCl (1.2 N) for 1-2 hours until it becomes soft. The 

liquid is decanted and washed with water until free of acid. Demineralized mass 

is boiled in 5% caustic soda for few minute. The liquid portion containing protein 

is filtered and the residue is washed with water until free of alkali. The wet mass 

is dried under sun and the product obtained is chitin which is pulverized to 

required mesh size before bagging.

Preparation of chitosan

Chitin is mixed with 40 % solution of caustic soda and heated by indirect steam 

at 90-100 °C in steam jacketed kettle for 90-120 minutes. During heating, 

samples are drawn at intervals from reaction mixture washed free of alkali and 

tested for solubility in 1% acetic acid. Completion of deacetylation is indicated 

by complete solubility in acetic acid. At the end, caustic soda solution is drained 

off and residue is washed until free from alkali, dried in sun. Chitosan is 

pulverized to required mesh size before bagging.

11.4. Uses of Chitin and Chitosan

Chitin and chitosan have been successfully used as food wraps due to their film 

forming properties. Chitosan has been widely used in vastly diverse fields, ranging 

from waste management to food processing, medicine and biotechnology. It 

becomes an interesting material in pharmaceutical applications due to its 

biodegradability and biocompatibility, and low toxicity.

• As clarifying agent of food juices and in purification of drinking water

• Thickening and stabilizing agent in food

• Treatment of waste and sewage water

• In cosmetics as a moisturizer and for protection against UV rays

• As a base for chromatography

• As a haemostatic agent in surgery and dentistry

• In fiber, films and membranes

• Important characteristic of chitosan films is these films are tough, long-lasting, 

flexible and very difficult to tear.

• Chitosan coating offers a great advantage in preventing microbial surface 

growth on foods. It would allow the inhibition of development of Listeria 

monocytogenes while being a biopackaging.

• Chitosan has found wide applicability in conventional pharmaceutical devices 

as a potential formulation excipient.

• The use of chitosan in novel drug delivery as mucoadhesive, peptide and gene 

delivery, as well as oral enhancer have been reported in the literature.

• Chitosan exhibits myriad biological actions such as hypocholesterolemic, 

antimicrobial, and wound healing properties.

• Since chitosan is a new substance, it is important to carry out precise 

standardization for its pharmaceutical and biomedical applications like other 

auxiliary substances.