**1. Introduction**

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Polysaccharides are natural, non-toxic and biodegradable polymers that cover the surface of most cells and play important roles in various biological mechanisms such as immune response, adhesion, infection and signal transduction. Investigations on the alternative treatments applied by different cultures throughout the history revealed the fact that the utilized plants and fungi were rich in bioactive polysaccharides with proven immunomodu‐ latory activity and health promoting effects in the treatment of inflammatory diseases and cancer. Hence considerable research has been directed on elucidating the biological activity mechanism of these polysaccharides by structure-function analysis [1].

Hemicelluloses are structural polysaccharides which are the second most abundant hetero‐ polymers present in nature accounting for one third of total components available in the plants (Figure 1) [2]. Mannans and xylans are the two most important hemicelluloses and hence a lot of research is mainly focused on their value-added applications and hydrolysis [3]. Mannan is a biodegradable and bioactive polysaccharide that has been a focus of interest by various sectors due to its valuable properties. The film forming capacity and biodegradability of mannans make them an interesting alternative to the petroleum-based materials. Mannanbased films and coatings were shown to exhibit low oxygen and grease permeability and, in some cases, relatively high tensile strength [4]. There are also interesting reports on the successful use of mannan as a bioactive material in health related applications.

Mannans are linear polymers of 1,4-linked mannose residues and contain less than 5% of galactose [5]. In nature, mannan is present in four different forms, each having a β-1,4-linked backbone containing mannose (linear mannan) or a combination of glucose and mannose residues (glucomannan) and occasional side chains of α-1,6-linked galactose residues (galac‐

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tomannan / galactoglucomannan). The mannose and glucose residues in the backbone are sometimes acetylated at C-2 or C-3 (3,5).

section of the chapter will involve conclusions and future prospects on microbial mannan

Mannan as a Promising Bioactive Material for Drug Nanocarrier Systems

http://dx.doi.org/10.5772/58413

313

Mannan is one of the important member of the hemicellulose family and can be divided to four subfamilies: linear mannan, glucomannan, galactomannan, and galactoglucomanan [14]. Mannan is present in different forms, each having a β-1,4-linked backbone containing mannose (linear mannan) or a combination of glucose and mannose residues (glucomannan) and occasional side chains of α-1,6-linked galactose residues (galactomannan / galactoglucomann‐ an) (Figure 2). In the backbone, mannose and glucose units can also be acetylated at C-2 or C-3

Glucomannan is mainly a straight-chain polymer, with a small amount of branching. The component sugars are β-(1,4)-linked D-mannose and D-glucose with a reported ratio of 1.6:1 [15], or 1.4:1 [16]. Softwoods and hardwoods consist of glucomannan with a glucose/mannose ratio of 1:3 and 1:1.5–2, respectively [17-20]. There is a significant similarity between confor‐ mation of glucomannan chains and those of cellulose A two-fold screw axis was observed because of the extended chains. Due to axial position of the hydroxyl group at C-2 of mannose, the interaction between C-6 and O-2 atoms of contiguous residues is prevented, and the chains are loosened, weakening the packing and organization [17]. Different structures were reported for glucomannans isolated from different sources. For example, (1 → 4)-linked structure, acetyl groups at C-2, C-3 positions and O-acetyl group at C-6 position were reported for glucomannan extracted from seeds of *Lupinus* [21]. Irregular distribution of acetyl groups was reported for pine glucomannan [22]. Studies on a nonionic glucomannan with a main chain of β-(1 → 4) linked mannopyranosyl units to which D-glucopyranosyl units are linked by α-(1 → 6)

production and its potential uses in nanotechnology.

**2. Structure of mannans**

**Figure 2.** Four different forms of mannan

(3,5) .

**Figure 1.** Polysaccharide composition of plants

In plants, mannans have a structural role by binding cellulose, but also they serve a storage function as a reserve carbohydrate in endosperm walls and vacuoles of seeds and vacuoles in vegetative tissues [5]. Recently, mannan has also been proposed as a signaling molecule in plant growth and development [6].

Mannan is a biodegradable and bioactive polysaccharide that has been a focus of interest by various sectors due to its valuable properties. The film forming capacity and biodegradability of mannans make them an interesting alternative to the petroleum-based materials. Mannanbased films and coatings were shown to exhibit low oxygen and grease permeability and, in some cases, relatively high tensile strength [4]. There are also interesting reports on the successful use of mannan as a bioactive material in health related applications. Mannan conjugated to vaccine preparations are already in the clinic [7,8]. Tang et al. [9] utilized a mannan-based system to target DNA vaccines to antigen presenting cells and demonstrated that it could induce far stronger immune responses in mice compared to naked DNA immu‐ nization. By further studies, they could explain the molecular basis of the observed immune enhancing attributes of mannan-based DNA vaccination [9]. Successful use of carboxylic mannan-coated iron oxide nanoparticles in targeting immune cells for *in vivo* lymph nodespecific Magnetic Resonance Imaging was also reported recently [10]. Moreover, to target mannose receptor expressed on the surface of antigen-presenting cells, biocompatible selfassembled mannan nanogels were designed to provide a therapeutic or vaccine delivery platform [11,12]. In a recent review on oral drug delivery research in Europe, mannan based nanogels were considered as a new approach for the oral delivery of labile molecules [13].

In this chapter, after a brief description of mannan, its production by algae, fungi, bacteria and other eukaryotic microorganisms will be mentioned with special focus on microbial resources. Then, use of mannan as a bioactive material in nanocarrier systems for drug delivery appli‐ cations will be covered in detail by giving examples from literature and industry. The final section of the chapter will involve conclusions and future prospects on microbial mannan production and its potential uses in nanotechnology.
