because of an increased desire to explore underutilized resources (mainly shell
wastes) for the isolation of chitin and make it suitable for various biomedical
applications. The basic approach is more or less same for the isolation of chitin
from various sources because, typically, the exoskeleton of crustaceans consists of
minerals (especially calcium carbonate), protein, chitin, pigments, etc. No economical
and appropriate solvent is, however, known for the dissolution of chitin after
isolation of chitin from these exoskeletons. The current industrial method for
obtaining chitin from the exoskeletons is to make the calcium carbonate and
proteins in the exoskeletons soluble in water and then to remove them from the
exoskeletons to obtain chitin. Specifically, the exoskeletons of crabs, lobsters, or
shrimps are immersed in a dilute aqueous alkaline solution and heated, after
which the degraded proteins are washed off with water. Insoluble matter with
chitin contained therein is immersed in a dilute aqueous solution of hydrochloric
acid to convert the calcium carbonate (which is still contained in the insoluble
matter) into calcium chloride, which is soluble in water. The insoluble matter is
then washed with water to remove the calcium chloride, so that chitin is
obtained as insoluble matter. The various sources of chitin differ somewhat in
their structure and percentage chitin content. Usually, chitin isolation consists of
several steps, i.e., demineralization, deproteinization, and decoloration. The first
two steps can be reversed according to the need for recovery of carotenoids and
protein and for further chitin application. Among other crustacean shells, crab
and shrimp shells have received significant attention for the production of chitin
and chitosan [22, 23]. The readers can find out about traditional isolation of
chitin in many reviews, research articles, patents, and books [24–33]. Succinctly,
demineralization is usually achieved by using diluted hydrochloric acid (1–8%)
at room temperature [34, 35]. To prevent chitin depolymerization,
ethylenediamine tetraacetic acid (EDTA) can be used for removal of mineral
salts [36, 37]. On the other hand, deproteinization involves the usage of aqueous
sodium or potassium hydroxide solution, and decoloration is usually carried out
by a bleaching treatment with NaOCl or H 2 O 2 solutions [38].
The most exploited sources of chitin are shrimp and crab shells. Lertsutthiwong
et al. [28] has studied the effect of chemical treatment on the characteristics of
chitosan obtained from fresh local black tiger shrimp shells. In this study, they
treated the shrimp shells by reversing the conventional order of extraction of chitin
from crustacean shells. The differences in the characteristics of chitin produced by
different serial treatments are shown in Table 1. Further, they showed the effect of
these different serial treatments on the quality of chitosan obtained from chitin after
deacetylation. If process 2 is followed by subsequent deacetylation then there is a
possibility of obtaining chitosan with high viscosity because the protein layer
becomes protected from more hydrolysis, and vice versa in the case of process 1
(see Table 2). To obtain chitosan with a high viscosity and a high degree of
deacetylation at low temperature, the process should be initiated with decalcification and requires multi-deacetylation.
There are many standard operating procedures available for extraction of chitin
and chitosan because of their wide ranges of sources [39–45]. Although lots of work
90
J. Dutta
wastes) for the isolation of chitin and make it suitable for various biomedical
applications. The basic approach is more or less same for the isolation of chitin
from various sources because, typically, the exoskeleton of crustaceans consists of
minerals (especially calcium carbonate), protein, chitin, pigments, etc. No economical
and appropriate solvent is, however, known for the dissolution of chitin after
isolation of chitin from these exoskeletons. The current industrial method for
obtaining chitin from the exoskeletons is to make the calcium carbonate and
proteins in the exoskeletons soluble in water and then to remove them from the
exoskeletons to obtain chitin. Specifically, the exoskeletons of crabs, lobsters, or
shrimps are immersed in a dilute aqueous alkaline solution and heated, after
which the degraded proteins are washed off with water. Insoluble matter with
chitin contained therein is immersed in a dilute aqueous solution of hydrochloric
acid to convert the calcium carbonate (which is still contained in the insoluble
matter) into calcium chloride, which is soluble in water. The insoluble matter is
then washed with water to remove the calcium chloride, so that chitin is
obtained as insoluble matter. The various sources of chitin differ somewhat in
their structure and percentage chitin content. Usually, chitin isolation consists of
several steps, i.e., demineralization, deproteinization, and decoloration. The first
two steps can be reversed according to the need for recovery of carotenoids and
protein and for further chitin application. Among other crustacean shells, crab
and shrimp shells have received significant attention for the production of chitin
and chitosan [22, 23]. The readers can find out about traditional isolation of
chitin in many reviews, research articles, patents, and books [24–33]. Succinctly,
demineralization is usually achieved by using diluted hydrochloric acid (1–8%)
at room temperature [34, 35]. To prevent chitin depolymerization,
ethylenediamine tetraacetic acid (EDTA) can be used for removal of mineral
salts [36, 37]. On the other hand, deproteinization involves the usage of aqueous
sodium or potassium hydroxide solution, and decoloration is usually carried out
by a bleaching treatment with NaOCl or H 2 O 2 solutions [38].
The most exploited sources of chitin are shrimp and crab shells. Lertsutthiwong
et al. [28] has studied the effect of chemical treatment on the characteristics of
chitosan obtained from fresh local black tiger shrimp shells. In this study, they
treated the shrimp shells by reversing the conventional order of extraction of chitin
from crustacean shells. The differences in the characteristics of chitin produced by
different serial treatments are shown in Table 1. Further, they showed the effect of
these different serial treatments on the quality of chitosan obtained from chitin after
deacetylation. If process 2 is followed by subsequent deacetylation then there is a
possibility of obtaining chitosan with high viscosity because the protein layer
becomes protected from more hydrolysis, and vice versa in the case of process 1
(see Table 2). To obtain chitosan with a high viscosity and a high degree of
deacetylation at low temperature, the process should be initiated with decalcification and requires multi-deacetylation.
There are many standard operating procedures available for extraction of chitin
and chitosan because of their wide ranges of sources [39–45]. Although lots of work
90
J. Dutta