Synthesis and characterization of chitosan from marine sources in Black Sea

Chitosan has been extracted from different marine crustacean from the Black Sea of Bulgarian Gulf. The contents of the various exoskeletons have been analyzed and the percent of the inorganic salt , protein, chitinand chitosan was determined. Deacetylation of the different chitin produced was conducted by the conventional thermal heating method. The chitosan was characterized by elemental analysis, FTIR measurements. Key wards: Chitosan , demineralization, deprotenization,deacetylation, FTIR spectroscopy INTRODUCTION Chitosan is chemically defined as a copolymer of α-(1,4) glucosamine (C6H11O4N)n, with a varying content of N-acetyl groups. It is produced by deacetylation of chitin [1,8,12]. Figure 1 indicates the chemical structure of glucosamine, which is the building unit of chitosan. Fig. 1 Chemical and 3D-structure of N-Dglucosamine As a naturally occurring polysaccharide, chitosan shows many unique properties, such as biocompatibility, biodegradation, biological activity and low-toxicity [18]. Consequently, chitosan and its derivatives have drawn the attention of multidisciplinary research groups. The characteristics of chitosan in solutions depend on the degree of deacetylation (DD), the distribution of acetyl groups, the chain length, the molecular weight distribution, and the solubility [2]. Among the most important features of chitosan in solution is the conformation of this polymer at the surfaces and in the bulk phase. Consequently conformational studies may contribute to the understanding of different phenomena related to the interaction between chitosan and the solvent. The conformational flexibility of chitosan was previously reported, and is attributed to the presence of the free primary amino groups [9,13,14,22]. It was concluded that conformational changes occur from looser chain to coiled sphere upon increasing concentration of chitosan solutions [13]. However, these studies were carried out on widely dispersed high molecular weight samples. Because of low molecular weight chitosans are more suitable for incorporation in liquid drug delivery systems, it becomes necessary to understand their conformational behavior in aqueous solutions. Several techniques to extract chitosan from different sources have been reported. The production of chitosan from crustacean shells obtained as a food waste is economically feasible, especially if it includes the recovery of carotenoids. The shells contain considerable amount of astaxanthin, a carotenoids that have so far not been synthesized, and which are marked as a fish food additive in aquaculture. Chitosan itself was directly extracted from fungi by alkaline and acid treatment [4]. Some authors [15,23] have developed methods to use microorganisms or proteolytic enzymes НАУЧНИ ТРУДОВЕ НА РУСЕНСКИЯ УНИВЕРСИТЕТ 2010, том 49, серия 9.1 66 for the deproteinization of the crustacean chitin wastes in this way a more economic production of chitin and chitosan can be achieved. The most common method is referred to the chemical procedure [Sheme 1]. The chemical method for isolation of chitosan from crustacean shell biomass involves various major steps: elimination of inorganic matter (mainly calcium carbonate) in dilute acidic medium (demineralization) and chitin deacetylation. Usually demineralization is accomplished by using HCl followed by extraction of protein matter in alkaline medium (deproteinization). The later is traditionally done by treating shell waste with aqueous solutions of NaOH [Sheme 1]. The effectiveness of alkali deproteinization depends on the process temperature, the alkali concentration, and the ratio of its solution to the shells.