Antidiabetic Applications of Chitosan and Its Derivatives
Chitosan is a functional and basic linear polysaccharide prepared by N-deacetylation of chitin in the presence of alkali sodium hydroxide. Generally, deacetylation cannot be completely achieved even when subjected to harsh treatment. The degree of deacetylation usually ranges from 70% to 95%, depending on the method used. Thus, chitosan is available with various molecular weights and deacetylation degrees. Chitosan is insoluble in water, alkali, and organic solvents but is soluble in most solutions of organic acids when the pH of the solution is below 6. The industrial production and application elds of chitosan have been steadily increasing since the 1970s. Early applications of chitosan were centered on the treatment of wastewater, heavy metal adsorption, food processing, immobilization of cells and enzymes, resin for chromatography, functional membrane in biotechnology, animal feed, and so on. The recent trend is toward producing highly valuable industrial products, such as cosmetics, drug carriers, and pharmaceuticals. Chitin and chitosan are known to exhibit antitumor, antibacterial, hypocholesterolemia, and antihypertensive activity (Kim and Rajapakse 2005). The main motive for the development of new applications for chitosan lies in the fact that it is a very abundant polysaccharide and it is nontoxic and biodegradable. Despite its functions and importance as a biomaterial, the applications of chitosan in food and biomedical industries are narrowed owing to its poor solubility, high molecular weight, and viscosity. There is evidence to validate the non-or indigent absorption of chitin and chitosan in the human intestine owing to lack of enzymes to cleave the β-glucosidic linkage in chitosan. Because chitosan is a water-insoluble large biopolymer, it is difcult to be absorbed by the mammal body. In this respect, enzymatic hydrolysis of chitosan to obtain oligomers has gained considerable interest recently (Jeon and Kim 2000).