Crustacean shells

Amino-2-deoxy-a-D-glucose (a-D-Glucosamine) from Crustacean Shell, M. Stacey and J. M. Webber, Methods Carbohydr. Chem., 1 (1962) 228-230. 

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... 

Chitosan is a polymer of glucosamine and A-acetyl-glucosamine, obtained from crustacean shells. It has been used to lower blood lipid concentrations, for body weight reduction (26), and as an excipient in pharmaceutical formulations. 

Many of the elements in the ocean—the phosphorus and silicon in crustaceans shells and the copper in the blood of lobsters, for example—are essential to sea life. If just a few of these vital elements were to disappear, it would ruin the fishing industry and lead to famine in many parts of the world. 

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). 

Preussia sp. (preussin), 11 principal macromolecule in crustacean shells (chitin), 285 Prosopis africana (cassine, iso-6-cassine), 164, 174 Prosopis africana (isoprosopinine), 164, 174... 

Figure 8-7. The Australian Western Rock lobster has a red phase (top) and a white phase (middle) reprinted from Comparative Biochemistry and Physiology, Part B 141 authors Wade et al (2005) entitled Esterified astaxanthin levels in lobster epithelia correlate with shell colour intensity Potential role in crustacean shell colour formation pp. 307-313 Copyright (2005), with permission from Elsevier and the authors. The bottom schematic shows the Ufe cycle Figure from Wade 2005 with the permission of Dr. N. Wade and originally from the Western Australian Fisheries website http //www.fish.wa.gov.au/ (see color plate section)...

N. Wade Crustacean Shell Colour Formation and the White Phase of the Western Rock Lobster, Panulirus Cygnus . PhD thesis University of Queensland (2005). 

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. 

NATURAL RESOURCES Chitin is a biopolymer found in crustaceans shells (crab, shrimp, prawn, lobster) in some mollusks (krill, oyster, clam shells, squid skeleton). It is also found in fungi (mushrooms, yeast) and in various insects (cockroaches, silkworms, spiders, beetles). 

Chitin, the precursor of chitosan, is a nitrogen containing polysaccharide and is second most abundant biopolymer after cellulose. It is widely distributed in the shells of crustaceans such as crabs, shrimps, lobsters, prawns, squilla, etc., as well as in the exoskeleton of marine zoo-plankton, including coral, jellyfish, and squid pens. About 20-40% chitin is present the exoskeleton of these animals. It is also present in smaller quantities in insects such as butter flies ladybugs, and the cell walls of yeast, mushrooms, and other fungi [Fig. 19.4]. However, since the crustacean shells [crabs, shrimps, lobsters, etc.] are waste products of food industry, these are commercially employed for the production of chitin and chitosan [1, 4, 18], It is believed that at least 10 gigaton of chitin is synthesized and degraded and it is also estimated that over 150,000 tons of chitin is available for commercial use annually. 

Conversion of chitin into chitosan involves the deacetylation process, which is a harsh treatment usually performed with concentrated sodium hydroxide solution. Chitin flakes are treated in suspension with aqueous 40-50% caustic solution at 80-120°C with constant stirring for 4-6 h and this treatment is repeated once or more than once for obtaining high-amino-content product. To avoid depolymerization due to oxidation, sodium borohydrate is added. Excess alkali is drained off and the mixture is washed with water several times until it is free from alkali. Most of the alkali is then used either in deproteinization or in deacetylation. Excess water is removed in screw press and the wet chitosan cake is either sun dries or in drier at 60°C. Chitosan thus obtained is in the form of flakes and can be pulverized to powder. The flowchart for the manufacture of chitosan from the starting material (crustacean shells) is shown in Fig. 19.5. 

It is a linear polysaccharide composed of randomly distributed p-(l-4)-linked o-glucosamine (deacetylated unit) and V-acetyl-D-glucosamine (acetylated unit). It is made by treating shrimp and other crustacean shells such as crabs and krills with the alkali NaOH. Chitosan is a naturally abundant and renewable polymer and has excellent property such as biodegradability, biocompatibility, nontoxicity, and good adsorption [92]. The structure of chitosan is given in Figure 1.21. 

Crustacean shells consist of 30-40% proteins, 30-50% calcium carbonate, and 20-30% chitin and also contain pigments of a lipidic nature such as carotenoids (astaxanthin, canthaxanthin, lutein, and p-carotene). These proportions vary with species and with season. On the other hand, chitin is associated with a higher protein content but lower carbonate concentration. Chitin is extracted by acid treatment to dissolve the calcium carbonate followed by alkaline extraction to dissolve the proteins and by a depigmentation step to obtain a colorless product mainly by removing the astaxanthin [102]. 

Blends were prepared with cellulose or silk as soon as a common solvent was available [63, 69-71]. Recently, ionic liquids were used. The solvent l-ethyl-3-methyl-imidazolium acetate completely dissolves raw crustacean shells allowing to recover high purity chitin powder or films and fibres by direct spinning [72]. Films of poly(e-caprolactone) (PCL) blends with a-chitin and chitosan were produced. They are completely biodegradable and the crystallinity of PCL is suppressed in the blends due to hydrogen bond interaction between PCL and polysaccharides [73]. Blends were also realized with poly (3-hydroxybutyric acid) (PHB) and chitin or chitosan. They show faster biodegradation than the pure-state component polymers [74,75]. 

Qin, Y., Lu, X., Sun, N. and Rogers, R.D. (2010) Dissolution or extraction of crustacean shells using ionic liquids to obtain high molecular weight purified chitin and direct production of chitin film and fibers. Green Chemistry, 12,968-971. 

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