Chitin

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Current Chemical Biology, 2009, 3, 203-230

203

Functional Characterization of Chitin and Chitosan
Inmaculada Aranaz, Marian Mengíbar, Ruth Harris, Inés Paños, Beatriz Miralles, Niuris Acosta, Gemma Galed and Ángeles Heras* Department of Physical Chemistry II, Faculty of Pharmacy, Institute of Biofunctional Studies, Complutense University, Paseo Juan XXIII, nº 1. Madrid 28040, Spain Abstract: Chitin and its deacetylated derivative chitosan are natural polymers composed of randomly distributed -(1-4)linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit). Chitin is insoluble in aqueous media while chitosan is soluble in acidic conditions due to the free protonable amino groups present in the D-glucosamine units. Due to their natural origin, both chitin and chitosan can not be defined as a unique chemical structure but as a family of polymers which present a high variability in their chemical and physical properties. This variability is related not only to the origin of the samples but also to their method of preparation. Chitin and chitosan are used in fields as different as food, biomedicine and agriculture, among others. The success of chitin and chitosan in each of these specific applications is directly related to deep research into their physicochemical properties. In recent years, several reviews covering different aspects of the applications of chitin and chitosan have been published. However, these reviews have not taken into account the key role of the physicochemical properties of chitin and chitosan in their possible applications. The aim of this review is to highlight the relationship between the physicochemical properties of the polymers and their behaviour. A functional characterization of chitin and chitosan regarding some biological properties and some specific applications (drug delivery, tissue engineering, functional food, food preservative, biocatalyst immobilization, wastewater treatment, molecular imprinting and metal nanocomposites) is presented. The molecular mechanism of the biological properties such as biocompatibility, mucoadhesion, permeation enhancing effect, anticholesterolemic, and antimicrobial has been updated.

Keywords: Chitin, chitosan, molecular weight, deacetylation degree, crystallinity, functional characterization. 1. INTRODUCTION Among the novel families of biological macromolecules, whose relevance is becoming increasingly evident, are chitin and its main derivative, chitosan. Potential and usual applications of chitin, chitosan and their derivatives are estimated to be more than 200 [1]. This wide range of applications includes biomedicine, food, biotechnology, agriculture and cosmetics, among others. The importance of chitin and chitosan in the last years is evident in Table 1. Chitin and chitosan are described as a family of linear polysaccharides consisting of varying amounts of (1 4) linked residues of N-acetyl-2 amino-2-deoxy-D-glucose (denoted in this review as A residues) and 2-amino-2-deoxy-Dglucose residues (denoted in this review as D residues). Chitin samples have a low amount of D units and hence the polymer is insoluble in acidic aqueous media (Fig. 1a). On the other hand, the amount of D units in chitosan samples is high enough to allow the polymer to dissolve in acidic aqueous media. Some authors consider that chitosan is the polymer with at least 60% of D residues [2]. Chitin is the second most abundant natural polymer in nature after cellulose and it is found in the structure of a wide number of invertebrates (crustaceans’ exoskeleton, insects’ cuticles) and the cell walls of fungi, among others. On the other hand, chitosan only occurs naturally in some fungi (Mucoraceae) [3]. *Address correspondence to this author at the Institute of Biofunctional Studies, Complutense University, Paseo Juan XXIII, nº 1, Madrid 28040, Spain; Tel/Fax: +34-913943284; E-mail: aheras@farm.ucm.es; inma@ieb.ucm.es 1872-3136/09 $55.00+.00

Chitosan...
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