Chapter 1
Chitin and Chitosan: History, Composition and Properties

Annu1*, Shakeel Ahmed1,2 and Saiqa Ikram1*

1Bio/Polymers Research Laboratory, Department of Chemistry, Jamia Millia Islamia (A Central University), New Delhi, India

2Department of Textile Technology, Indian Institute of Technology Delhi, New Delhi, India

*Corresponding authors: annuchem92@gmail.com; sikram@gmail.com

Abstract

Chitin and chitosan are most abundant naturally occurring polymers, ranked second after cellulose. Chitin is generally extracted from natural sources viz. terrestrial organisms, marine organisms, microorganisms like fungi and enzymatically from crustaceans shell waste materials. On the other hand, chitosan is obtained from the deacetylation of the former, chitin.

Nowadays, chitin and chitosan are commercially manufactured from biowastes obtained from aquatic organisms. But due to the seasonal and capricious availability of raw materials, terrestrial crustaceans and mushrooms are the alternative source for their production. Structurally, chitin and chitosan are N-acetyl-D-glucosamine units and D-glucosamine units, respectively, with only difference in hydroxyl group of cellulose. Both the biopolymers are biodegradable and possess many beneficial properties such as biocompatibility, antimicrobian, hemostatic, anti-inflammatory, antioxidant, mucoadhesion, analgesic, non-toxicity, adsorption enhancing, antihypertensive, anticholesterolemic, anticancer, and antidiabetic. Due to having such respectable properties chitin, chitosan, and their corresponding derivatives are greatly exploiting by the scientists and also getting tremendously better results in medical and engineering fields.

Keywords: Chitin, chitosan, history, structure, properties, solubility, viscosity, biomedical, anticancer

1.1 Chitin

1.1.1 History

French scientist Prof. Henri Braconnot for the very first time discovered chitin in 1811 in mushroom. After that Odier found the same compound in the cuticles of insects in 1823 and called it "Chitin" from the Greek word meaning tunic, covering or envelope [1].

This was how it begins the research in a new direction of polymers present in our nature. Gradually as the time passed away in 1859, Prof. C. Rouget coined another noval biopolymer, actually derived from previous chitin, and it was known as "Chitosan." In 1878, Ledderhose revealed that the chitin consists of glucosamine and acetic acid. Thereafter, in 1930s and 1940s, both former and latter attract considerable attention as evidenced by about 50 patents. Chitin is the most abundant naturally occurring polymer, ranked second after cellulose and also most abundant naturally occurring polysaccharide possesses amino acid and sugars. Chemically, chitin is composed of N-acetyl-D-glucosamine units with ß-(1-4) glycosidic linkage [2].

1.1.2 Sources of Chitin

Chitin is generally produced from natural sources viz. terrestrial organisms, marine organisms, microorganisms like fungi and enzymatically from crustaceans shell waste materials. On the other hand, chitosan is obtained from the deacetylation of the former, chitin. Nowadays, chitin and chitosan are commercially manufactured from biowastes obtained from aquatic organisms. But due to the seasonal and capricious availability of raw materials terrestrial crustaceans and mushrooms are the alternative source for their production [2]. The industrial manufacturing of synthetic polymers was restricted by the time because of the inadequate facilities as well as the cutthroat competition in synthetic polymers. Therefore, again the shellfish shells, crustaceans and shrimps revitalized the interest in late 1970s (Global industry analysis since 2004). Various sources for extraction and production of chitin can be categorized as follows:

1. Terrestrial organisms
2. Marine or Aquatic organisms
3. Microorganisms (e.g., Fungi)

1.1.2.1 Terrestrial Organisms

From commercial point of view, these organisms are mainly used for the extraction of chitin, due to their easy availability and processability. Terrestrial species generally includes crustaceans such as Porcellio scaber, Armadillidium vulgare; arthropods, nematodes, insects, silkworms, mosquitoes, honeybee, Sipyloidea sipylus, Drosophila melanogaster, Extatosoma tiaratum, and many more [3]. As the composition of these organisms is quite different, there is a variation in the contribution to the percentage of chitin produced as depicted in Table 1.1.

Table 1.1 Percentage of chitin produced from different sources [3].

1.1.2.2 Marine or Aquatic Organisms

Chitin produced from aquatic species includes diatoms, algae, crabs, shrimps, lobster, squids, and krill. The hazardous waste materials generated from head, thorax, shells, and claws of shellfish are utilized as raw materials for processing, containing 15-40% chitin, 20-40% proteins, and 20-50% CaCO3. The waste streams of molluscs and crustaceans are the main source of chitin. Also they constitute a rich source of proteins, flavor compounds, and various pigments and hence are of great attention for different research fields and industries as well. Actually, if they are disposed of in the open environment of the water bodies, such as sea or river, then they are problematic due to the higher biochemical oxygen demand and eutrophication [4].

1.1.2.3 Microorganisms (e.g., Fungi or Mushroom)

Chitin can be obtained from microorganisms either by fermentative methods or biotechnological methods. Utilization of various microbes makes it easier for industries to produce chitin widely and hence microbes are considered as the economic source of extracting chitin as well as chitosan. Microbial world mainly includes fungi (cell wall, mycelia, septa) molds, chrysophyte algae, yeasts, prosthecate bacteria, spores of streptomycete and ciliates. Except Oomycetes, remaining Ascomycetes, Basidiomycetes, Deuteromycetes, and Zygomycetes consists of 2-65% chitin/chitosan. Especially, Mucoralean strains viz. Syncephalastrum racemosum and Cunninghamella echinulata cell wall exhibited maximum chitin/chitosan yield of 7% per mycelia dry weight under optimum conditions [5-7]. Some of the examples of extraction of chitin from terrestrial, marine and microorganisms are listed in Table 1.2.

Table 1.2 Examples of sources of extraction of chitin [5].

1.1.3 Extraction of Chitin

Chitin can be extracted from insect cuticle, tracheae and peritrophic matrix [25], shellfish waste such as shrimps, crabs, krill, lobster, fishes and microorganisms such as fungi or mushroom mycelia and some bacteria as discussed above. Generally, extraction of chitin involves the following steps:

1. Demineralization
2. Deproteination
3. Decolorization

There may be difference in the sequence of these steps [3, 8]. For instance, Kumari et al. described the extraction of chitin from fish scales of Labeo rohita but after demineralization they performed decolorization followed by deproteination [9].

1.1.3.1 Demineralization

It can be performed by using strong acids such as HCl, H2SO4, HNO3 and weak acids such as CH3COOH and HCOOH. But generally HCl seems to be best one. Previous researchers showed that the concentration of HCl was about 1N or...