Fish products and Byproducts Technology

Unit 11 - Chitin and Chitosan

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.