44
3 Chitin
of crab shells to obtain chitin for example (Castro et al. 2018). The fermentation
process therefore reduces the environmental impact of chemical chitin extraction.
The process could take up to 80 h as reported by different research studies (Cira
et al. 2002; Castro et al. 2018). Another advantage of the fermentation process is the
ability to recover the proteins for use as animal feed. Unlike the chemical process
where the deproteinization is done with a high concentration of alkali, the protein
extracted cannot be recovered and is usually discarded hence generating more waste.
Lactic acid bacteria (Lactobacillus sp.) fermentation of crustacean waste, for
example, involves the inclusion of a carbon source and in some cases mild acid such
as acetic acid to provide the right pH for the growth of the bacteria in the lag phase.
The lactic acid bacteria ferment the carbon source which could be whey, sugarcane
or other as well as the carbon present on the biowaste. Lactic acid is released as
a by-product of the fermentation process. The lactic acid reacts with the calcium
carbonate producing calcium lactate which precipitates and can then be separated by
washing. Proteolytic enzymes are produced from either the gut bacteria present on
the shrimp or strains added to the fermenter or the biowaste. These break down the
protein, leaving behind crude chitin. The low pH caused by the presence of lactic acid
and other by-products of the fermentation such as acetone also prevent the growth
of spoilage bacteria.
Lactococcus lactis, Terendinobacter turnarae, Lactobacillus plantarum, Lactobacillus pentosus and Lactobacillus salivarius are some examples of bacteria that
have been used in lactic acid fermentation of shell waste to produce chitin. Other
than the limited rate of demineralization and deproteinization achieved in chitin produced by fermentation, another concern is the microbial contamination of the chitin
produced (Gortari and Hours 2013). Any possible contamination makes this form of
chitin not suitable for human or animal consumption. For this reason, despite environmental and economic advantage posed by microbial extraction of chitin, many
of the applications of this method of chitin extraction have been limited to research
and laboratory experiments.
Other strains of organisms have been explored for production of chitin by fermentation. Filamentous fungi have also been used in the biological production of
chitin (Gortari and Hours 2013). The proteolytic enzymes are released by the fungi
which results in the deproteinization and demineralization of the shrimp shells. The
consequent release of amino acids in the process of deproteinization acts as the nitrogen source which the fungi require for growth and multiplication. This results in the
lowering of the pH of the system, thus aiding the demineralization of the shells.
3.5.6 Enzyme Extraction
Enzyme extraction involves the deproteinization of the shell waste through the action
of proteolytic enzymes. This has the advantage of not including microbes, thereby
minimizing the risk of microbial contamination of the product. However, the proteolytic enzymes only act to hydrolyze the protein; therefore, a pretreatment stage
3 Chitin
of crab shells to obtain chitin for example (Castro et al. 2018). The fermentation
process therefore reduces the environmental impact of chemical chitin extraction.
The process could take up to 80 h as reported by different research studies (Cira
et al. 2002; Castro et al. 2018). Another advantage of the fermentation process is the
ability to recover the proteins for use as animal feed. Unlike the chemical process
where the deproteinization is done with a high concentration of alkali, the protein
extracted cannot be recovered and is usually discarded hence generating more waste.
Lactic acid bacteria (Lactobacillus sp.) fermentation of crustacean waste, for
example, involves the inclusion of a carbon source and in some cases mild acid such
as acetic acid to provide the right pH for the growth of the bacteria in the lag phase.
The lactic acid bacteria ferment the carbon source which could be whey, sugarcane
or other as well as the carbon present on the biowaste. Lactic acid is released as
a by-product of the fermentation process. The lactic acid reacts with the calcium
carbonate producing calcium lactate which precipitates and can then be separated by
washing. Proteolytic enzymes are produced from either the gut bacteria present on
the shrimp or strains added to the fermenter or the biowaste. These break down the
protein, leaving behind crude chitin. The low pH caused by the presence of lactic acid
and other by-products of the fermentation such as acetone also prevent the growth
of spoilage bacteria.
Lactococcus lactis, Terendinobacter turnarae, Lactobacillus plantarum, Lactobacillus pentosus and Lactobacillus salivarius are some examples of bacteria that
have been used in lactic acid fermentation of shell waste to produce chitin. Other
than the limited rate of demineralization and deproteinization achieved in chitin produced by fermentation, another concern is the microbial contamination of the chitin
produced (Gortari and Hours 2013). Any possible contamination makes this form of
chitin not suitable for human or animal consumption. For this reason, despite environmental and economic advantage posed by microbial extraction of chitin, many
of the applications of this method of chitin extraction have been limited to research
and laboratory experiments.
Other strains of organisms have been explored for production of chitin by fermentation. Filamentous fungi have also been used in the biological production of
chitin (Gortari and Hours 2013). The proteolytic enzymes are released by the fungi
which results in the deproteinization and demineralization of the shrimp shells. The
consequent release of amino acids in the process of deproteinization acts as the nitrogen source which the fungi require for growth and multiplication. This results in the
lowering of the pH of the system, thus aiding the demineralization of the shells.
3.5.6 Enzyme Extraction
Enzyme extraction involves the deproteinization of the shell waste through the action
of proteolytic enzymes. This has the advantage of not including microbes, thereby
minimizing the risk of microbial contamination of the product. However, the proteolytic enzymes only act to hydrolyze the protein; therefore, a pretreatment stage