from shrimp shells and fungi by placing shrimp shells in direct contact with the
fermentation of filamentous fungi in a reactor so as to avoid the use of conventional
chemicals, which can lead to undue deacetylation of chitin or chain degradation
of the isolated chitin. Three proteolytic Aspergillus niger strains (0576, 0307, and
0474) were selected from a screening for protease activity from among 34
zygomycete and deuteromycete strains. The proteolytic enzymes released by the
fungi facilitate the deproteinization of shrimp powder and the release of hydrolyzed
proteins. The hydrolyzed proteins in turn act as a source of nitrogen for further
fungal growth, leading to a lowering of the pH of the fermentation medium, and
thereby further enhancing the demineralization of the shrimp-shell powder. Chitin
from non-fermented, fermented, and fungal mycelia were directly extracted
with 5% lithium-chloride–N,N-dimethylacetamide (5% LiCl in DMAc), a nondegradative solvent for chitin [36]. In this process, two different problems are
solved simultaneously without using any harsh chemicals. Fungal fermentation is
a cost-effective method compared to commercial protease enzymes that
deproteinize but not demineralize the shrimp shells.
Demineralization is also an important step in chitin purification from crabs. The
chemical method of demineralization includes the use of strong acid (HCl) that
harms the physicochemical properties of chitin. For the extraction of chitin from
trash crabs (Podophthalmus vigil), Das et al. [30] reported the use of organic acids
(lactic acid or other organic acids) produced by Lactobacillus plantarum as a
replacement for HCl for demineralization, and proteolytic enzymes produced by
A. niger as a substitute for alkaline aqueous solution for deproteinization. Although
the removal of protein entirely from crustacean shells has not yet been achieved
using biological treatment during isolation of chitin, the quality of chitin obtained
by this process compares well with chitin obtained by conventional chemical
treatment. The results of chitin derived from the trash crab are shown in Table 5.
The study showed that the effectiveness of lactic acid for the demineralization of
crustacean shells was virtually comparable to that of HCl. For effective removal
of minerals from crab shells using lactic acid, a shell to acid ratio of 1:25 and
temperature of 40
C were found to be satisfactory. The use of chemicals causes
depolymerization of chitin to a certain extent and, thus, its molecular weight as well
as viscosity are affected after solubilization [43] But, in this case, the combination
of lactic acid and A. niger not only produces partially soluble chitin, which is
anticipated to increase its applications in biomedicine and pharmacy, but also
reduces the production cost of chitin.
Chitosan is less commonly found in living organisms than chitin but it can be
found in the cell walls of certain groups of fungi. The traditional process of
obtaining chitosan is the deacetylation of chitin using strong caustic alkali but no
significant progress has yet been made in establishing new technologies for the
large-scale controlled production of chitosan. The recognition of chitin deacetylase
in several fungi and insects has given new momentum to the conversion of chitin
into chitosan. In contrast to the currently used chemical procedure, the use of
chitin deacetylase offers the possibility of a controlled non-degradable process,
resulting in the production of novel, well-defined chitosan oligomers and polymers.
Engineering of Polysaccharides via Nanotechnology
95
fermentation of filamentous fungi in a reactor so as to avoid the use of conventional
chemicals, which can lead to undue deacetylation of chitin or chain degradation
of the isolated chitin. Three proteolytic Aspergillus niger strains (0576, 0307, and
0474) were selected from a screening for protease activity from among 34
zygomycete and deuteromycete strains. The proteolytic enzymes released by the
fungi facilitate the deproteinization of shrimp powder and the release of hydrolyzed
proteins. The hydrolyzed proteins in turn act as a source of nitrogen for further
fungal growth, leading to a lowering of the pH of the fermentation medium, and
thereby further enhancing the demineralization of the shrimp-shell powder. Chitin
from non-fermented, fermented, and fungal mycelia were directly extracted
with 5% lithium-chloride–N,N-dimethylacetamide (5% LiCl in DMAc), a nondegradative solvent for chitin [36]. In this process, two different problems are
solved simultaneously without using any harsh chemicals. Fungal fermentation is
a cost-effective method compared to commercial protease enzymes that
deproteinize but not demineralize the shrimp shells.
Demineralization is also an important step in chitin purification from crabs. The
chemical method of demineralization includes the use of strong acid (HCl) that
harms the physicochemical properties of chitin. For the extraction of chitin from
trash crabs (Podophthalmus vigil), Das et al. [30] reported the use of organic acids
(lactic acid or other organic acids) produced by Lactobacillus plantarum as a
replacement for HCl for demineralization, and proteolytic enzymes produced by
A. niger as a substitute for alkaline aqueous solution for deproteinization. Although
the removal of protein entirely from crustacean shells has not yet been achieved
using biological treatment during isolation of chitin, the quality of chitin obtained
by this process compares well with chitin obtained by conventional chemical
treatment. The results of chitin derived from the trash crab are shown in Table 5.
The study showed that the effectiveness of lactic acid for the demineralization of
crustacean shells was virtually comparable to that of HCl. For effective removal
of minerals from crab shells using lactic acid, a shell to acid ratio of 1:25 and
temperature of 40
C were found to be satisfactory. The use of chemicals causes
depolymerization of chitin to a certain extent and, thus, its molecular weight as well
as viscosity are affected after solubilization [43] But, in this case, the combination
of lactic acid and A. niger not only produces partially soluble chitin, which is
anticipated to increase its applications in biomedicine and pharmacy, but also
reduces the production cost of chitin.
Chitosan is less commonly found in living organisms than chitin but it can be
found in the cell walls of certain groups of fungi. The traditional process of
obtaining chitosan is the deacetylation of chitin using strong caustic alkali but no
significant progress has yet been made in establishing new technologies for the
large-scale controlled production of chitosan. The recognition of chitin deacetylase
in several fungi and insects has given new momentum to the conversion of chitin
into chitosan. In contrast to the currently used chemical procedure, the use of
chitin deacetylase offers the possibility of a controlled non-degradable process,
resulting in the production of novel, well-defined chitosan oligomers and polymers.
Engineering of Polysaccharides via Nanotechnology
95