CHITOSAN

Chitin was described for the first time in 1811 by Braconnot, who was professor of Science of Nancy, France. Chitosan was discovered by Rouget in 1859. He was found that chitin, which has been boiled in a very concentrated potassium hydroxide solution, becomes soluble in diluted solutions of iodine and acid, where as chitin was stained brown.

The production of chitin and chitosan is currently based on crab and shrimp shells discarded by the canning industries in Oregon, Washington, Virginia, and Japan and by various finishing fleets in the Antarctic. Several countries possess large unexploited crustacean resources e.g. Norway, Mexico, and Chile. The production of Chitosan from crustacean shells obtained, as a food industry waste is economically feasible, especially if it includes the recovery of carotenoids. The shells contain considerable quantities of astaxanthin, a carotenoid that has so far not been synthesized, and which is marketed as fish additive in aquaculture, especially for Salmon.

Chitin and Chitosan:

Chitin, poly- (1,4)-2 acetomido-2-deoxy-ß-D-glucose, is the second most abundant natural polymer. Its chemical structure is similar to that of cellulose, differing only in the second carbon position where the hydroxy groups are replaced by an amino acetyl group. Chitosan is the deacetylated form of chitin, i.e. poly- (1,4)-2amido-2-deoxy- ß-D-glucose. Chitin and chitosan are widely distributed in animals and fungi and are the basic polysaccharides that are the major component of the shells of crustacean such as crab, shrimp and crayfish.
Chitin and chitosan have the potential to reduce and to solve some problems for creating “Greener environment

The following is a chronological order of the processes needed to produce Chitosan from crustacean shells

Crustacean
Shell—Size reduction—Protein Separation (NaOH)—Washing—Demineralization (HCl) – Washing and Dewatering – Chitin -- Deacetylation (NaOH) – Washing and Dewatering – Chitosan.

Chitin and Chitosan are natural resources refined from the waste products of the crabbing and shrimp industry. Chitin is produced from the processing waste of shellfish, frill, clams, oysters, squid, and fungi. They have a high percentage of Nitrogen (6.89%) compared to the synthetically substituted cellulose, which has 1.25% nitrogen. Chitosan has amino groups and hence it exhibits many properties, such as biodegradability, which are different from the cellulose. Chitin does not melt; it is insoluble in water, dilute acids, cold alkalies, and organic solvents. However, the solvents like formic acid, concentrated mineral acids, and tetrechloroacetic acid can dissolve Chitin, but they are not convenient and lead to polymer degradation. On the other hand, Chitosan is readily soluble in most aqueous solutions, like that of 5% formic acid and acetic acid because of the basicity of the primary amine groups. Chitosan dissolves readily when electric repulsions (corresponding to cationic charges)
are more important than the attracting interactions (such as hydrogen bonding and Vander Walls interactions). The solubility of chitosan is also favoured by the process of hydration of various, mainly charged sites. As a result, the ratio between NH₃⁺ and NH₂ groups, a parameter directly related to the charge density of the polymer, is a very important factor in ascertaining the properties of chitosan. The basic difference between
Chitin and Chitosan is the degree of deacetylation (DAC), which is the same as the relative amount of free amount amine. Chitosan is obtained from chitin by treating the latter with strong caustic soda and heat, which removes the N-acetyl groups.

As a natural renewable resource with a number of unique properties, chitosan is now attracting more and more scientific and industrial interest from diversified fields such as chemistry, biochemistry, medicine, pharmacology, biotechnology, and food and textile sciences. Properties such as biodegradability, biocompatibility, non-toxicity, wound healing and antimicrobial activity have generated much research work. Many unique products have been developed for various applications such as surgical sutures, artificial skin, cosmetics and dietary foods.

Almost all properties of chitin and chitosan depend on two fundamental parameters; the degree of acetylation and the molecular mass distribution (or average molecular weight), although they do have some contrasting properties. The molecular weight of chitin and chitosan can be determined by methods such as chromatography, light scattering and viscometry. Viscometry is by far the most simple and rapid method for the determination of average molecular weight by measuring an intrinsic viscosity for several concentrations of chitosan or chitin solutions.

Properties of Chitosan:

• Solution properties of Chitosan in free Amine (-NH₂) form soluble in acidic solutions.
• Insoluble at pH’s> 6.5
• Insoluble in H₂SO₄
• Limited solubility in H₃PO₄
• Insoluble in most organic solvents
• Soluble at pH’s < 6.5
• Forms viscous solutions
• Solutions shear thinning, forms gels with polyanions
• Will remain soluble in some alcohol-water mixtures
  

Chemical properties of Chitosan

Chitosan is a linear polyamine (poly-O-glucosamine) with reactive hydroxyl and amine group

Biocompatibility
Chitin and chitosan are natural biopolymers. They have no antigenic properties, and thus are perfectly compatible with living tissue. Their antithrombogenic and hemostatic properties make them very suitable for use in all fields of biology.

Cicatrizant
Chitosan forms films that are permeable to air. It facilitates cellular regeneration while protecting tissue from microbe attack. In addition, chitosan has been found to have a biostimulant effect on the regeneration of tissue.
Lysozome that kills various germs increases 1.5 to 2 times as fiber made from chitosan comes in contact with the skin it also activates nitrogen, which regenerates the skin. This property has allowed it to be used in making an
artificial skin for skin grafts on high degree burns and in surgical applications such as chitin suture thread. It binds to mammalian gum tissue. It accelerates the formation of osteoblasts responsible for the formation of bone.

Anticholesterolemic agent
Chitosan can trap lipids at their insolubilization pH in the digestive tract. Administered to rats, chitosan considerably reduces the level of cholesterol in the blood.

Chelation agent
Chitin and its derivatives are remarkable chelation agents. Chitosan is used for a wide rangeof applications: as a chromatography medium, or for trapping heavy metals, or for water treatment. It chelates many transitional metal ions

Biodegradable
Chitin and chitosan are biodegradable biopolymers. Enzymes-chitinase and chitosanase-break them down into oligopolymers that are then dealt with by the metabolism. It is biodegradable to normal body constituents.

Strengthening the immunity
Fibers made from chitosan strengthen the immunity of the human body to expel foreign matters when disease germs or viruses enter the body.

Antimicrobial activity
It is also a fungi static and has spermicidal and antitumor properties. Generally chitosan (D.A.=9.9%, concentration 0.15%) is proved to be free from mildew activity during four cultivating days. The activity increases with increase in concentration of chitosan.

Electric properties of Chitosan
Fibers made from chitosan can effectively generate static electricity due to its high molecular weight. It has a unique resistance value similar to other natural high molecular matters such as cellulose or rayon.

Deodrant properties of Chitosan
Chitosan eliminates stink of sweat and other odors. It has humid retention properties due to the amine radical & is also a central nervous system.

This post is contributed by Imran Mallick, M. Tech, UICT (formerly UDCT)