The complex world of polysaccharides edited by Desiree Nedra Karunaratne

 

The Complex World of Polysaccharides 

 

8 

the chitosan molecule. Thus, chitosan behaves like a polycation in solution [32]. Properties 

of chitosan, such as the mean polymerization degree, the degree of N-deacetylation, the 

positive charge, and the nature of chemical modifications of its molecule, strongly influence 

its biological activity. 

Chitin contains 6–7% nitrogen and in its deacetylated form, chitosan contains 7–9.5% 

nitrogen. In chitosan, between 60 to 80% of the acetyl groups available in chitin are removed 

[33]. The chain distribution is dependant on the processing method used to obtain 

biopolymer [34-36]. It is the N-deacetylated derivative of chitin, but the N-deacetylation is 

almost never complete [35]. Chitin and chitosan are names that do not strictly refer to a fixed 

stoichiometry. Chemically, chitin is known as poly-N-acetylglucosamine, and in accordance 

to this proposed name, the difference between chitin and chitosan is that the degree of 

deacetylation in chitin is very little, while deacetylation in chitosan occurs to an extent but 

still not enough to be called polyglucosamine [37]. 

 

Figure 3.

 Chitin and chitosan chemical structure 

9. Sources of chitosan 

Chitosan is commercially produced from deacetylated chitin found in shrimp and crab shell. 

However, supplies of raw materials are variable and seasonal and the process is laborious 

and costly [38]. Furthermore, the chitosan derived from such process is heterogeneous with 

respect to its physiochemical properties [38]. Recent advances in fermentation technology 

provide an alternative source of chitosan. Fungal cell walls and septa of Ascomycetes, 

Zygomycetes, Basidiomycetes and Deuteromycetes contain mainly chitin, which is responsible 

for maintaining their shape, strength and integrity of cell structure [38]. The production of 

chitosan from fungal mycelia has a lot of advantages over crustacean chitosans such as the 

degree of acetylation, molecular weight, viscosity and charge distribution of the fungal 

chitosan. They are more stable than crustacean chitosans. The production of chitosan by 

fungus in a bioreactor at a technical scale offers also additional opportunities to obtain 

identical material throughout the year. The fungal chitosan is free of heavy metal contents 

such as nickel, copper [39-41]. Moreover the production of chitosan from fungal mycelia 

gives medium-low molecular weight chitosans (1–12 × 10

4

 Da), whereas the molecular 

weight of chitosans obtained from crustacean sources is high (about 1.5 ×10

6 

Da) [41]. 

Chitosan with a medium-low molecular weight has been used as a powder in cholesterol 

absorption [42] and as thread or membrane in many medical-technical applications. For 

these reasons, there is an increasing interest in the production of fungal chitosan.  

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Is Chitosan a New Panacea? Areas of Application 

 

9 

There are some examples of chitosan extracted from fungi. Chitosans isolated from 

Mucorales typically show Mw in the range 4 x 10

5

 to 1.2 x 10

6

 Daltons and FA values 

between 0.2 and 0.09. Amino acid analysis of chitosan prepared from Aspergillus niger 

reveals covalently bound arginine, serine, and proline. Nadarajah et. al., 2001, studied 

chitosan production from mycelia of Rhizopus sp KNO1 and KNO2, Mucor sp KNO3 and 

Asperigullus niger with the highest amount of extractable chitosan obtained at the late 

exponential phase. Mucor sp KNO3, produced the highest amount of 557mg per 2.26 g of 

dry cell weight /250 ml of culture. Kishore et. al.(1993), examined the production of 

chitosan from mycelia of Absidia coerulea,  Mucor rouxii,  Gongronella butieri, Phvcomyces 

blakesleeanus and Absidia blakesleeana. Chitosan yields of A. coerulea, M. rouxii, G. butieri, P. 

blakesleeanus and A. blakesleeana were 47–50, 29–32, 21–25, 6 and 7 mg/100 mL of medium, 

respectively. The degree of acetylation of chitosan ranged from 6 to 15%; the lowest was 

from strains of A. coerulea. Viscosity average molecular weights of fungal chitosans were 

equivalent, approximately 4.5 x 10

5

 Daltons. Wei-Ping Wang et.al., (2008) evaluated the 

physical properties of fungal chitosan from Absidia coerulea (AF 93105), Mucor rouxii (Ag 

92033), and Rhizopus oryzae (Ag 92033). Their glucosamine contents and degrees of 

deacetylation (DD) were over 80%, differences had been observed in their molecular 

weight (Mw), ranging from 6.6 to 560 kDa. Chitosan was isolated and purified from the 

mycelia of Rhizomucor miehei and Mucor racemosus with a degree of deacetylation of 97 y 98 

respectively [43-45]. 

Considerable research has been carried out on using mycelium waste from fermentation 

processes as a source of fungal chitin and chitosan. It is argued that this would offer a stable 

non-seasonal source of raw material that would be more consistent in character than 

shellfish waste, but so far this route does not appear to have been taken up by chitosan 

producing companies. Currently there is only one commercial source of fungal chitosan and 

is produced by the company Kitozyme. However their raw material is not mycelium waste 

from a fermentation process, which is what is normally envisaged when fungal chitosan is 

referred to, but actually conventional edible mushrooms grown under contract in France 

and shipped to Belgium for processing. So mycelium waste still remains a vast and as yet 

untapped potential source of chitosan. 

10. Genetic engineering approach to produce chitin 

It is difficult to obtain pure carbohydrates, especially chitin, through conventional 

techniques. Bacterial cells have been engineered in an effort to overcome this problem [46]. 

E. coli has been engineered to produce chitobiose. This method took advantage of NodC, 

which is a chito-oligosaccharide synthase, and genetically engineered chitinase to make a 

cell factory with the ability to produce chito-oligosaccharides [47]. Recombinant chito-

oligosaccharides have also been obtained using E coli cells which expressed nodC or nodBC 

genes [48]. By expressing different combinations of nod genes in E. coli, O-acetylated and 

sulfated chito-oligosaccharide have been produced [49]. 

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