Biopolymers for Biomedical and Biotechnological Applications. Группа авторов

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Figure 2.5 Deacetylation reaction of chitin to chitosan.

      Source: Croisier and Jérôme 2013 [206]. Reproduced with permission of Elsevier.

Microbial chitin is a cell‐wall component of several yeast and fungi strains, conferring rigidity and protection to the cells [208,209]. Depending of the fungal source, chitin can achieve a cell‐wall content up to 60% on a dry basis [207]. It is also possible to find chitin polysaccharides in some algae species [210,212].

      Fungal chitin can also be found covalently linked to β‐glucans to form chitin complexes such as chitin–glucan complex (CGC) [208,213]. Among the microbial cultures that can be used as chitin/chitinous polysaccharide sources are filamentous fungi (e.g. Aspergillus niger, Aspergillus fumigatus, Rhizopus oryzae, Mucor rouxii) [213,217], mushrooms (e.g. Ganoderma lucidum, Agaricus bisporus, Schizophyllum commune) [218,221], and yeasts (e.g. Saccharomyces cerevisiae, Komagataella (Pichia) pastoris, Candida albicans) [216,222–224]. The chitinous polysaccharide extraction from fungal cell walls can be performed with mechanical and/or nonmechanical methods. Some examples of mechanical methods are high‐pressure homogenization, bead mill, or ultrasound, while the nonmechanical methods include the alkaline hydrolysis (with NaOH or KOH as solvents) or enzymatic treatments [225].

      Chitosan is the most known chitin derivative, obtained from the deacetylation reaction of chitin, in high alkali and temperature conditions or by enzymatic hydrolysis (Figure 2.5) [226,228]. Depending on the alkaline treatment performed for fungal cell‐wall lysis, the extraction procedure can also result in the extraction of chitosan or chitosan–glucan complex (ChGC) [215,221,229,230].

      2.7.2 Properties of Chitinous Polysaccharides

      Chitin is a crystalline and hydrophobic polysaccharide with a molecular weight of 1 to 2 × 10⁵ Da [226,227,231,232]. Chitinous polysaccharides, such as CGC, also have a similar molecular weight (4 to 5 × 10⁵ Da), but since they are covalently linked to β‐glucans, they present an amorphous nature [222]. Chitin and chitinous polysaccharides are insoluble in water and in most of organic solvents. The most common solvent systems used for these biomaterials are N,N‐dimethylacetamide/LiCl, NaOH/urea, LiOH or NaOH at low temperatures, or, more recently, ionic liquids [227,231,233]. In opposition, chitosan is soluble in diluted organic acids such as acetic, formic, or hydrochloric acid solutions [227,231]. Chitosan is also characterized for its high deacetylation degree (DD), usually above 50% and a molecular weight of 2 × 10⁴ to 2 × 10⁵ Da [216,234].

      Chitin, chitosan, and their complexes are also known by their biological activity. Behind being biodegradable and biocompatible, these polysaccharides also have antimicrobial, anti‐inflammatory, antioxidant, and antitumoral activity [235,237]. Moreover, fungal chitosan also has emulsifying properties with vegetable oils [214].

      2.7.3 Applications of Chitinous Polysaccharides

      In application development of microbial chitinous polysaccharides, several polymer structures can be constructed from nanofibers or nanoparticles for food formulations or biomedical devices, hydrogels for drug delivery systems or films, and scaffolds/composites or tablets for pharmaceutical formulations [155,215,238,239].

The diversity of polymer structures and their physicochemical and biological properties have attracted an increasing interest on these polysaccharides for several and diverse areas, such as biomedical devices, pharmaceutical industry, food products, cosmetic formulations, agriculture, and textiles or even on wastewater treatment (Table 2.4) [234,235,241].

Table 2.4 Microbial chitinous polysaccharide properties and applications.

      2.7.3.1 Biomedical Applications

Chitin, chitosan, and chitinous polysaccharides have been subject of increasing interest on the biomedical field due to their biocompatibility, biodegradability, and nontoxicity [237]. Moreover, these polysaccharides also have biological activity including anticancer and antibacterial activity [234]. They are also immunostimulating, antithrombogenic, hemostatic, and wound healing [234,235]. These properties make these biopolymers interesting materials for drug delivery systems, tissue engineering, or wound healing products.

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