ReviewAdvances in characterisation and biological activities of chitosan and chitosan oligosaccharides
Introduction
Chitin is the most abundant polysaccharide in natural macromolecules, next to cellulose, as the major component of the shells of crustaceans, such as crabs and insects. Although chitin has many functional specialties in various areas, the low water solubility and poor biodegradation performance restricts its applications. As the degraded products of chitosan or chitin, chitosan oligosaccharides (COS) have recently been produced by several methods, such as enzymatic and acidic hydrolysis. The degraded products have a smaller molecular weight, and are readily soluble in aqueous solutions, making COS perform valuable biological activities at the cellular or molecular level. The study of COS has been increasing not only for the regeneration characteristics of abundant natural resources, but also for their biological compatibility and effectiveness. There are numerous reports on the biological activities of COS and their potential applications in food (Du, Wang, Yuan, Wei, & Hu, 2009), pharmaceutical (Berger, Reist, Mayer, Felt, & Gurny, 2004), agricultural, and environmental industries (Crini, 2005). As natural antioxidants (Xie, Xu, & Liu, 2001), COS possess multiple properties, such as anti-inflammatory, antimicrobial (Choi et al., 2001), hypocholesterolemic (Muzzarelli et al., 2006), immunostimulating (Feng, Zhao, & Yu, 2004), and anti-tumour activity (Salah et al., 2013). Moreover, the features of innately biocompatible, non-toxic, and non-allergenic to living tissues have made COS a promising drug carrier and tissue-engineering scaffold for nano-/micro-architecture (Dash, Chiellini, Ottenbrite, & Chiellini, 2011). This review summarises the preparation methods and modification of COS, discusses well-known biological activities of COS, and highlights the anti-tumour property and its relevant mechanisms. The future utilisation and potential development is also elucidated.
Section snippets
Characterisation of chitosan and COS
Chitosan is the N-deacetylated form of chitin and linear polysaccharides with a variable degree of N-acetylation, which is composed of less than 20% β-(1,4)-2-acetamido-d-glucopyranose and more than 80% β-(1,4)-2-amino-d-glucopyranose (Fig. 1A). Chitosan is water-insoluble and highly viscous in dilute acidic solutions. This solubility drawback may restrict the applications of chitosan in biological fields. In contrast, as the hydrolysed products of chitosan, COS have better solubility and lower
Biological activities of COS
Chitosan and COS have attracted considerable interests because of their biological activities and potential applications in food, pharmaceutical, agricultural, and environmental industries. Recent advances have highlighted the health benefits of COS including antihypertensive, lowering of blood cholesterol, and anti-infectious and anti-tumour effects. Although there has been an increase in studies of the biological activities of COS, no single type of chitosan or COS exerts all the
Prospect
Many functional products, such as chitosan capsules and COS capsules are available commercially, and COS for medical use have also been prepared based on their biological activities. Because no single type of COS exerts all biological activities, different chitosan derivatives have different structures and physicochemical properties, which may result in novel findings of biological activities and bioactive compounds. Therefore, modification of COS will contribute to synthesis polymers with
Conclusion
As has been summarised, chitosan and chitosan oligosaccharides (COS) possess various biological activities, which largely depend on the physicochemical properties, including the degree of deacetylation (DD), molecular weight (also known as degree of polymerisation or DP), and cationic nature. The advantages and disadvantages of chemical and enzymatic hydrolysis methods were demonstrated. Several biological activities were concluded, by the description of proposed mechanisms and relevant
Acknowledgment
The study was financially supported by the National Natural Science Foundation of China (No. 31000831), Agriculture Science Technology Achievement Transformation Fund (No. 2008GB23260349) and Research Fund for Post-doctor of Heilongjiang Province (No. LBH. Q12085).
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