Chitin, Chitosan and Their Complexes

Chitin exists in three polymorphic forms, depending on the arrangements of the chains in the microfibrils a-, [)- or y-chltin, in which the molecules have antiparallel, parallel or mixed arrangements, respectively. The most common form is a-chitin [45], being found in shrimp, prawn, crab and lobster shells, while p-chltin is found in mol-lusks such as squids [86] y-chitin is found in the cell walls of fungi [118]. 

Currently, commercial chitin and chitosan are extracted from industrial shellfish processing wastes (shrimp, crab, lobster). The seasonal character of those raw materials and the variability of the composition of the organisms make the process of chitin extraction rather expensive with low reprodudbillty. Moreover, they are subjected to environmental variations that impact on the products supply and quality [14,40,116]. Chitin is extracted from crustacean shells by the use of strong adds and/or bases that can cause deacetylation and depolymerization of chitin [119]. Alternative methods include the use of enzymes or proteolytic microorganisms (e.g.. Pseudomonas malto-philia, Bacillus subtilis. Streptococcus faecium, Aspergillus oryzae) that hydrolyze shellfish proteins and leave the associated chitin intact [119]. 

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