40
3 Chitin
Pretreatment
Shell
waste
Demineralization
Deproteinization
Drying
Purification
Chitin
Deacetylation
Chitosan
Fig. 3.3 Processes in extraction of chitin
In the following sections, typical example processes are given for extraction of
chitin from crustacean shells: mushrooms, insects and fish scales. The difference in
extraction processes from one source to another is due to the variation in the structural
composition of the shell or other parts of the organisms from which chitin is to be
extracted. The yield from a particular source also varies with extraction methods and
the efficiency of the process. Chitin could be lost during separation and purification
processes.
3.5.1 Extraction from Crustacean Exoskeleton
Crustaceans are characterized by the presence of a hard shell forming an exoskeleton
which serves mainly structural roles and some role in calcium regulation in the
organism (Ahearn et al. 2004). These hard shells consist of chitin fibers within a
protein matrix calcified with calcium carbonate and calcium phosphate (Gadgey and
Bahekar 2017). These shells have sites for muscle attachments such that the wastes
from their processing may also contain some lipids and other proteins and compounds
such as carotenoids.
Extraction of chitin from exoskeletons of crustaceans generally involves three
main stages. One stage is removal of the protein in a process referred to as the deproteinization, and this is achieved by immersing the shells in alkali solution. Sodium
hydroxide is most commonly used for this. The next stage is then to remove the calcium content which is mainly acid-soluble calcium carbonate. This is referred to as
the demineralization step. Since calcium carbonate and most minerals are soluble in
acidic solutions, the demineralization process is carried out by immersing the deproteinized residue in acid solution. While hydrochloric acid is most widely used, other
acids such as nitric acid (HNO 3 ), sulfuric acid (H 2 SO 4 ), acetic acid (CH 3 COOH) and
oxalic acid (HCOOH) can also be used for demineralization. The type of acid used
3 Chitin
Pretreatment
Shell
waste
Demineralization
Deproteinization
Drying
Purification
Chitin
Deacetylation
Chitosan
Fig. 3.3 Processes in extraction of chitin
In the following sections, typical example processes are given for extraction of
chitin from crustacean shells: mushrooms, insects and fish scales. The difference in
extraction processes from one source to another is due to the variation in the structural
composition of the shell or other parts of the organisms from which chitin is to be
extracted. The yield from a particular source also varies with extraction methods and
the efficiency of the process. Chitin could be lost during separation and purification
processes.
3.5.1 Extraction from Crustacean Exoskeleton
Crustaceans are characterized by the presence of a hard shell forming an exoskeleton
which serves mainly structural roles and some role in calcium regulation in the
organism (Ahearn et al. 2004). These hard shells consist of chitin fibers within a
protein matrix calcified with calcium carbonate and calcium phosphate (Gadgey and
Bahekar 2017). These shells have sites for muscle attachments such that the wastes
from their processing may also contain some lipids and other proteins and compounds
such as carotenoids.
Extraction of chitin from exoskeletons of crustaceans generally involves three
main stages. One stage is removal of the protein in a process referred to as the deproteinization, and this is achieved by immersing the shells in alkali solution. Sodium
hydroxide is most commonly used for this. The next stage is then to remove the calcium content which is mainly acid-soluble calcium carbonate. This is referred to as
the demineralization step. Since calcium carbonate and most minerals are soluble in
acidic solutions, the demineralization process is carried out by immersing the deproteinized residue in acid solution. While hydrochloric acid is most widely used, other
acids such as nitric acid (HNO 3 ), sulfuric acid (H 2 SO 4 ), acetic acid (CH 3 COOH) and
oxalic acid (HCOOH) can also be used for demineralization. The type of acid used