Chitin from Crustacean shells

The normal procedure for preparation of chitin from crustacean shells includes the use of NaOH, HC1, and decoloring agents to remove the remaining proteins, calcium, and color, respectively. The chitin that is produced can then be deacetylated with sodium hydroxide to produce chitosan (Tsai et al., 2002). Jaworska and Konieczna (2001) reported that chitosan can be prepared via chemical means using concentrated hydroxides (40-50%) at high temperatures (100-130 °C). 

A Enzymatic Production of Chitin from Crustacean Shell Waste... 

Indeed, the use of biological treatment instead of chemical treatment for the isolation of chitin from crustacean shells as well as for production of chitosan will substantially reduce environmental pollution. The use of chitin deacetylase for the preparation of chitosan polymers and oligomers offers the possibility to develop an enzymatic process that could potentially overcome most of the drawbacks discussed earlier [59]. As shown in Fig. 4, chitin deacetylase (CDA EC 3.5.1.41) catalyzes the hydrolysis of A-acetamido bonds in chitin to produce chitosan. The presence of this enzyme has been reported in several fungi and insect species [60-68]. 

Broadly, the three different steps involved in the preparation of chitin from crustacean shells can be classified as demineralization, deproteinization and decoloration, which is then followed by its alkaline deacetylation for the synthesis of chitosan [10,11]. Briefly, the outer crustacean shells are initially removed from the shrimps and crabs and washed with cold water, dried in the sun and demineralized with 1.25 N HCl at room temperature. The shells are then washed with water to remove acid and calcium chloride. They are then deproteinated by boiling with 5% sodium hydroxide (NaOH) for 15 min. This process of deproteinization is repeated to completely remove the protein content from the shells and then washed with water to neutrality. It is then decolorized with acetone to remove the remaining pigments and the resultant product is chitin, which is then dried imder the sun [12,13],... 

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]. 

A contrasting picture is seen for chitosans. Chitosans—as considered in detail in the following Chapter—are derivatives of chitin (after an alkali extraction procedure) and are available in large quantities from the shells of crabs, lobsters and other crustaceans. Pure chitin is poly-N-acetylglucoasmine. The N-acetyl groups are de-acetylated in chitosan to an extent represented by ei-... 

Chitin, a homopolymer from pi 4-linked N-acetylglucosamine, is the most important structural substance in insect and crustacean shells, and is thus the most common animal polysaccharide. It also occurs in the cell wall of fungi. 

The crude chitin is isolated from the outer skeletons of crustaceans, molluscs or invertebrate animals, insects, and certain fimgi. Commercially, crab and shrimp shells are the major sources of chitin. Crustacean shells not only consist of 30 0% protein, 30-50% calcium carbonate, and... 

Industrial chitin is obtained from marine food production waste, i.e., crustacean shells from shrimp, crab or krill [13,14]. The processing of shrimps for human consumption generates 40-50% of the total mass of marine food production waste, which is considered to be one of the main pollutants in coastal areas, as it is dumped into the sea [15]. A small part of the waste is dried and used as chicken feed [14].The major components (on dry mass basis) of shrimp waste are chitin, minerals, carotenoids and proteins thus, the utilisation of this shell food waste as an alternative source to produce chitin may help solve environmental problems related to waste generation. 

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