Biodegradability, chitin/chitosan

There are many kinds of natural biodegradable polymers. They are classified into three types according to their chemical structures, i.e., polysaccharides, polypeptides/proteins and polynucleotides/nucleic acids. Among them, polysaccharides, such as cellulose, chitin/chitosan, hyaluronic acid and starch, and proteins, such as silk, wool, poly( y-glutamic acid), and poly(e-lysin), are well known and particularly important industrial polymeric materials. 

Chitin, chitosan, and their derivatives offer a wide range of applications including bioconversion for the production of value-added food products, preservation of foods from microbial spoilage, formation of biodegradable films, recovery of waste material from food processing discards, purification of water, and clarification and deacidification of fruit juices (Shahidi et al., 1999) (Table II). 

There is also interest in other sources of natural polymers that are both biobased and biodegradable. Starting materials include chitin, chitosan, casein, hemicellu-lose, and others. None of these materials have yet reached the point of commercial applications as packaging materials. 

Chitosan, the deacetylated product of chitin, is obtained by treating chitin with 40% caustic soda at elevated temperatures. In contrast to chitin, chitosan is soluble in dilute mineral acids. It is used for making biodegradable food packaging film, as an additive to improve the wet strength of paper, as an ion exchanger in water treatment, and to cover wounds. 

Chitin, a polysaccharide-based material, is present in the shells of such sea creatures as shrimps and crabs. Chitin is biodegradable by nature, and when acetyl groups i.e. CH3-CO, are removed from the chitin molecules, chitosan is produced with exposed amine groups. The antimicrobial capabilities of chitin/chitosan are based on its cationic nature, which is capable of binding with anionic pathogens and making them ineffective (Aranaz et a/.,2009,p203). 

Biodegradable polymers can be classified into three categories according to their origin (i) synthetic polymers, particularly aUphatic polyesters, such as poly (L-lactide) (PLA) [1-3], poly(e-caprolactone) (PCL) [4—6], poly(p-dioxanone) (PPDO) [7-9], and poly(butylene succinate) (PBS) [10-12] (ii) polyesters produced by microorganisms, which mainly correspond to different poly(hydroxyalkanoate)s (e.g., poly(P-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate)) and (iii) polymers derived from natural resources (e.g., starch, cellulose, chitin, chitosan, lignin, and proteins). 

Kamble et al (2007) reported on the applicability of chitin, chitosan and chemically modified chitosan (20%-lanthanum chitosan) as adsorbents for the removal of excess F from drinking water. Chitosan which is derived from chitin is one of the main components of crustacean shells of prawn, crab, shrimp or lobster, has the ability to coordinate metal ions because of its high concentration of amine functional groups (Li et al, 1992). It is also a non-toxic, biodegradable and biocompatible material. Furthermore, the effects of various physico-chemical parameters such as pH, adsorbent dose, initial F concentration and the presence of interfering ions on adsorption of F were assessed by Kamble et al (2007). The authors concluded that lanthanum chitosan adsorbents were better at removal of F from water than plain chitosan and chitin (Fig. 6.2). 

The industrial and pharmacological applications of chitin and chitosan have been known for many years and have become an important industrial pursuit because these materials have the three advantages of being abundant, nontoxic, and biodegradable. Chitin and chitosan are produced on an industrial scale from the shells of crustaceans. Chitosans are strong chelators of arsenic and heavy cations, and are used for this purpose in wastewater treatment and in the paper industry (Da Sacco and Masotti, 2010). They have many other applications, however, particularly in the biomedical field, either unaltered or after chemical transformation (depolymerization, alkylation. 

Proteins and carbohydrates are the most important and renewable biological polymeries which are frequently used in the industrial and medicinal fields. Most enzymes catalyzing the primary degradation of protein and carbohydrates are hydrolase enzymes. Apart from these polymers, a relatively lower amount of natural polymers such as natural rubber, nucleic acids and lignin, are available. In this section, the biodegradation mechanisms of the more abundant and well-known natural polymers, such as proteins, cellulose, starch, chitin, chitosan, nucleic acids, and their derivatives, are omitted because many excellent reviews and books are available. 

Recently, numerous approaches have been studied for the development of cheaper and most effective adsorbents containing biopolymers. The most widespread biopolymers are polysaccharides [190], chitin [167, 139, 7] and cyclodextrin [157, 26, 32]. These biopolymers reach the increasing demand for treatment of industrial wastewater before their use or disposal. Because the pollutants creates environmental and health diffieulties, associated with heavy metals and pesticides and their deposit through the food chain [39]. Traditional methods for the elimination of heavy metals from industrial wastewater may be inefficient or costly, particularly when metals are present at low concentrations [30, 184]. Chitin, chitosan and oligosaccharides represent interesting and attractive alternative adsorbents because of their particular structure, physico-chemical characteristics, chemical stability, high reactivity and excellent selectivity towards metals. Moreover, Ihey are abundant, renewable and biodegradable resources and have a capacity to associate by physical and chemical interactions with a wide variety of molecules [22, 131]. 

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