Chitin is a high molecular weight ubiquitous material occurs abundantly on the earth next to cellulose, was first described by Braconnot at 1811. Chitin is extensively act as a major structural component of shells of crustaceans, exoskeleton of insects and cell walls of bacteria and fungi. Chitin is structurally insoluble linear mucopolysaccharide consisting repeated units of N-acetyl –D-glucosamine (GlcNAc) linked by β-(14) glycosidic bonds. Structurally chitin is highly similar to cellulose, the difference is hydroxyl [-OH] group of C-2 position in cellulose is replaced by an acetamido [-NHCOCH3] group in chitin. Chitin is widely distributed but specifically extracted from shellfish waste such as shrimps, crabs and crawfish. In general the chitin collected as a complex network in crustaceans consists of 30- 40% of protein, 30-50% calcium carbonate and 20-30% of chitin. The morphological views present chitin in α and β form. α-chitin is in a massive amount and can be located at fungal yeast cell walls, krill, lobster and crab tendons, in shrimp cells and also in insect cuticle. The β- chitin found in rare amount i.e. associated with proteins of squid pens. Both α and β chains are arranged in sheet and detained by intra sheet hydrogen bonds. The presence of inter sheet hydrogen bonds in α- chitin prevents the diffusion of smaller molecules into the crystalline state.
Chitin is hydrophobic in nature and insoluble in water and organic solvents. Commercially chitin are extracted by following three steps.
- Demineralization ( Calcium carbonate and phosphate separation)
- Deproteinization (protein separation), and
- Decolorization (removal of pigments)