Natural Polymers and their Biological Activities - Natural Antioxidants and Biocides from Wild Medicinal Plants - page 210

with acetic anhydride. The action of chitosan
with molecular weights from 1.4 × 10 3 to 4.0 ×
10 5 Da against S. aureus, E. coli and Candida
albicans was determined. The water-soluble
half N-acetylated chitosans and chitooligomers
do not have significant antimicrobial activity.
Moreover, water-insoluble chitosan and chi-
tooligomers promote the growth of C. albicans .
In contrast, water-insoluble chitosans with a
molecular weight of around 5.0 × 10 4 Da
present a better antimicrobial action in these
tested samples. The antimicrobial mechanism
of water-insoluble chitosan was hypothesized
to form an impervious layer around the cell.
The antimicrobial activity of chitooli-
gosaccharides with different degrees of
deacetylation and polymerization was evalu-
ated on several fungal and bacterial species.
The antimicrobial activity of chitooligosac-
charides increased with an increase in
deacetylation but decreased with an increase
in polymerization. The chitooligosaccha-
rides showed a major antimicrobial activity
against bacteria rather than fungi. However,
the antimicrobial activity of chitooligosac-
charides was significantly higher than that of
chitosan because the low degree of polymeri-
zation of the chitooligosaccharides allows
them to penetrate the cell membrane of the
microorganisms, interact with DNA in the
cytoplasm and lead to a mistake in DNA rep-
lication, resulting in the suppression of
microbial growth (Wang et al ., 2007).
Recently, Lillo et al. (2008) studied the
antibacterial activity of chitooligosaccha-
rides obtained by partial acid hydrolysis of
chitosan. The fraction corresponding to the
molecular weight of 10,000 Da was modi-
fied by reductive alkylation of the amine
group of chitooligosaccharide with d -(+)
glucosamine hydrochloride in the presence
of sodium cyanoborohydride and afforded
the aminoglicosylated derivative shown in
Fig. 14.4. This derivative has a prominent
antibacterial activity against S. aureus .

high-value biopolymers with a variety of
industrial applications. Various types of
EPS have been used in medicine, foods, cos-
metics and other industries. They have
potent biological and pharmacological
activities, including immune-stimulating,
anti-tumour and hypoglycaemic activities.
In particular, many kinds of EPS have been
produced from submerged cultures of
mushrooms or entomopathogenic fungi
(Kim et al ., 2003).
The exopolysaccharide of Paecilomyces
tenuipes C240 is highly valued because of
its various biological and pharmacological
activities including its immuno-stimulating
and antitumor activities (Xu et al ., 2003).
Although many studies have examined the
effect of culture conditions on the produc-
tion of microbial polysaccharides, little is
known about the influence on the product
quality, particularly molecular characteris-
tics. Several investigators have pointed out
that culture medium and environmental
conditions affect the production and the
physico-chemical characteristics of exopol-
ysaccharides (Xu and Yun, 2004; Xu et al .,
2006).
Takagi and Kadowaki (1985) optimized
the submerged culture conditions to pro-
duce the exopolysaccharide 1→4-2-amino-
2-deoxy-a- d -galactan (Fig. 14.5), also known
as poly-a- d -galactosamine, from the fungi
Paecilomyces sp. I-1. Poly-a- d -galactosamine
may constitute an important starting
material for fine chemicals and biologically
active derivatives. It is known that it exhib-
its anti-tumoural effects and bacterial
activity. It shows similar physicochemical
properties to chitosan, but the easy produc-
tion of this polysaccharide, and its stability
against enzymes or microorganisms capable
of hydrolysing glucosamine residues, are
advantages over chitosan.
Lillo and Matsuhiro (2003) studied the
growth kinetics of Paecilomyces sp. and the
production of EPS. The major production of
EPS is obtained in four-day cultures. On the
other hand, the concentration of the EPS is
inversely proportional to the increase in the
biomass of the fungus. This decrease in the
production of EPS probably could be due to
the exhaustion of the carbon source in the

14.3 Fungal Polysaccharides

The microbial exopolysaccharides (extra-
cellular polysaccharides; EPS) are a class of