Crustacean shell waste chitin

A Enzymatic Production of Chitin from Crustacean Shell Waste... 

Overview of Biological Treatment of Crustacean Shell Wastes for Chitin Production... 

Cellulose and chitin are recognized as the first and the second most myriad of polysaccharides, respectively. Generally, chitin s resources are crustaceans like crab, prawn, lobster, and shrimp shell waste. Chitin is also widely distributed in marine-like invertebrates, insects, fungi, and yeast. Chitin is a long-chain polysaccharide composed of linear P-l,4-linked units of N-acetyl-D-glucosoamine (Rinaudo 2006). Chitosan is a biopolymer derived from chitin by deacetylation of acetyl groups (CO-CH3) (Figure 6.1). 

As chitin is found abundantly in the exoskeleton of crustaceans, the large quantity of crustacean shell waste from the seafood industry provides sufficient amount of raw materials for the synthesis of chitin and chitosan. The proteins, lipids, pigments, and calcium deposits in the crustacean shell waste are removed chemically, and chitin is extracted after passing through several steps. Then the chitin is A-acetylated by alkali treatment or acid treatment to form chitosan, which is more important for the production of COS (Figure 38.2). However, the preparation of... 

However, crustacean shell wastes are extensively used for the production of chitosan because the percentage availability of chitin is higher compared to other sources. Therefore, the approximate composition of different crustacean shell wastes are given in Table 7. 

Shell wastes from shrimp, crab, and lobster processing industries are the traditional source of chitin. However, commercial production of chitosan by deacetylation of crustacean chitin with a strong alkali appears to have limited potential for industrial acceptance because of seasonal and limited supply, difficulties in processing, particularly with the large amount of waste of concentrated alkaline solution causing environmental pollution, and inconsistent physico-chemical properties (Chatterjee et ah, 2005). 

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). 

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. 

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. 

Currently, commercial chitin and chitosan are extracted from industrial shellfish processing wastes (shrimp, crab, lobster). The seasonal character of those raw materials and the variability of the composition of the organisms make the process of chitin extraction rather expensive with low reprodudbillty. Moreover, they are subjected to environmental variations that impact on the products supply and quality [14,40,116]. Chitin is extracted from crustacean shells by the use of strong adds and/or bases that can cause deacetylation and depolymerization of chitin [119]. Alternative methods include the use of enzymes or proteolytic microorganisms (e.g.. Pseudomonas malto-philia, Bacillus subtilis. Streptococcus faecium, Aspergillus oryzae) that hydrolyze shellfish proteins and leave the associated chitin intact [119]. 

Chitin, a poly(saccharide) closely related to cellulose and shown in Figure 4, is being studied by many research groups for a wide variety of biomedical, agricultural and cosmetic applications. Chitin is found mainly in insect and crustacean shells. Most current research centers on the deacetylated chitin, which is called chitosan. Figure 5. Chitosan is now finding some new uses in the textile industry, waste water treatment and medicine.While neither material is likely to be made synthetically on a commercial scale, both polymers are derived from formerly useless... 

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. 

Commercial chitin is extracted from crustacean wastes of the fishing industry, the main chitin sources being the shells of shrimp, crab, lobster, prawn and krill. These crustacean wastes consist of chitin (20-30 per cent), protein... 

Chitin (poly(N-acetyl-D-glucosatnine)) represents the second most abundant polysaccharide after cellulose. It is found in the exoskeleton of crustaceans and insects and in the cell wall of fungi and microorganisms [23], Arthropod shells (exoskeletons), the most easily accessible sources of chitin, contain 20-50% of chitin on a dry basis. Wastes of seafood processing industries ate used for the commercial production of chitin. 

The biomaterials available in the largest quantities on the Earth are cellulose and chitin, being easily isolated and processed into many articles and chemical forms. The manufacture of wood pulp is a worldwide business and the conversion of shellfish waste into chemical chitin is now an established industry. These materials are closely related polysaccharides and are found in nature as structural materials cellulose is found in the cell walls of plants and chitin is found in the shells of marine crustaceans. These structures are indicated in Fig. 12.1. 

---