Shell structure, crustacean

The spectral variations caused by the interference phenomena become relevant when a food contains tightly adjoining dense structures like feathers, fish scales, or the shells of crustaceans. 

It is found as a component of fungal and bacterial cell-walls, in insect cuticles, and as the shell of crustaceans. Being so similar to cellulose in chemical composition, its structure is important, if for no other reason than that comparison of the two structures might aid in our understanding of each. The similar fibrillar fine-structure (see Fig. 12) of these two polysaccharides is noteworthy, as the lateral forces between molecules are different. Although chitin does not occur in Nature specifically as a fiber, it is frequently found well-oriented in bristles and as tendon material. Samples from invertebrates are usually admixed with protein and carbonate, both of which must be removed before x-ray diagrams of high quality can be obtained. 

Chitin is poly[j5-(l->4)-iV-acety 1-2-amino-2-deoxyglucopyranose]. The shells of crustaceans contain 20-25% chitin together with 70% calcium carbonate. It is the second most important biological animal structural material after the protein collagen. 

Chitin is the second most abundant organic compound in nature after cellulose. It is found mainly in the animal kingdom, where it is the main structural polysaccharide in the exoskeleton (shells) of crustaceans, insects and other invertebrates. It also occurs in some algae, fimgi, yeasts and bacteria, usually associated with proteins. Naturally occurring chitin is consumed only rarely. Some beetles and sea foods with shells (such as crabs and snails) are eaten as delicacies, and are largely made of chitin. The chitin content in the exoskeleton of crabs is 61-77%. 

Chitin is a naturally occurring polysaccharide existing in the outer shells of crustaceans, insect exoskeletons, and fungal ceU walls. It is the second most abundant natural polymer after cellulose. Chitin is commercially produced from the shell waste of crabs, shrimps, and kriUs through a series of deproteinization and demineralization processes to remove the protein and minerals, which together with chitin form the composite structure of the shells. The dry mass of shell waste typically contains about 15-25% of chitin. 

Chitin is a polysaccharide that has a structure very similar to that of cellulose and the bacterial cell wall polysaccharide murein. The structure of chitin is essentially the structure of cellulose, with the hydroxyl group at C-2 of the D-glucopyranose residue substituted with an A -acetylamino group [132] (see Fig. 6.15A). Chitin is the structural polysaccharide that replaces cellulose in the cell wall of many species of lower plants. It is found in fungi, yeast, green algae, and brown and red seaweed cell walls. Chitin is also the major component of the exoskeleton of insects. It is found in the cuticles of annelids, molluscs, and in the shells of crustaceans such as shrimp, crab, and lobster [133]. 

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. 

Many polysaccharides besides starch and cellulose are important components of animal tissues, or play a vital role in biochemical processes. One example is chitin, a celluloselike material that is the structural component of the hard shells of insects and crustaceans. The difference between chitin and cellulose is that instead of being a polymer of glucose, chitin is a polymer of 2-deoxy-2-A-ethanamidoglucose (M-acetyl-jS-D-glucosamine) ... 

Mammals rely on bones and muscles, which are made primarily of proteins, to give their bodies structure and support. However, insects and crustaceans, such as crabs and lobsters, rely on hard shells made of the polysaccharide chitin for structure. 

Chapters 3 and 4 investigate representatives of the invertebrate groups in the intertidal zone, the small animals. These organisms include sponges, cnidarians, worms, mollusks, crustaceans, and echinoderms. In the coastal food chain, these invertebrates feed on plants and animals and serve as food for larger organisms. Most are protected by structures such as shells or spines or by toxic chemicals. 

Chitin is a homopolymer of AT-acetyl-D-glucosamine residues and is a major structural component in the exoskeletons of crustaceans, mollusks, arthropods, and the cell walls of numerous fungi and algae. Owing to its widespread presence in both terrestrial and aquatic organisms, chitin is second only to cellulose as the most abundant biopolymer on the Earth (Shahidi and Abuzaytoun, 2005). On a dry weight basis, shrimp, crab, lobster, prawn, and crayfish have been reported to contain between 14% and 35% chitin, while deproteinized dry shell waste of Antarctic krill contains approximately 40% crude chitin (Haard et al, 1994). Crustaceans are the primary sources of chitin used in industry. Chitin can be extracted from shellfish and crustacean waste by mixing with a dilute add to induce demineralization, followed by a deproteini-zation step in a hot alkaline solution (Synowiecki and Al-Khateeb, 2003). 

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