Biology Reference
In-Depth Information
14
Natural Polymers and
their Biological Activities
Luis Lillo,* Julio Alarcón, Gerardo Cabello,
Carlos L. Céspedes and Claudia Caro
14.1
Basic Polysaccharides
targets of chemical modification (Fig. 14.1)
(Hirano
et al
., 1987).
The antimicrobial activity of chitosan
against a variety of bacteria and fungi is greater
than that of chitin. Its biological activity is
based on the presence of the free amino group
at carbon 2 in the
d
-glucosamine units that, in
acidic conditions, are charged positively. These
groups interact with negative macromolecule
residues that are located at the cellular surface
of the bacterium, inhibiting its growth.
Chitosan of low molecular weight and
oligosaccharides of this biopolymer pre-
pared by acid and enzymatic depolymeriza-
tion have strong antibacterial and antifungal
activities (Kurita, 2001; Kumar
et al
., 2004).
The chitooligosaccharides are prepared
through enzymatic hydrolysis using chito-
nases. The oligosaccharides of a molecular
weight in the rank of 10,000 Da present a
greater antibacterial activity. The molecular
size of the chitooligosaccharides is of great
importance in the inhibition of microbial
growth (Jeon
et al
., 2001).
A series of chitooligosaccharide deriva-
tives obtained by chemical modfication
had a high antimicrobial activity on
Strep-
tococcus mutans
, the main etiological agent
of dental caries in humans. Oligosaccharides
of chitosan (COS) were reacted with glycidyl
The basic polysaccharides are composed of
units of amino sugar usually N-acetylated.
These polysaccarides and their derivatives
have applications in industry, medicine and
biochemistry (Muzzarelli, 1985; Yalpani,
1985). Chemical modification of the amino
group of basic polysaccharides allows the
introduction of new functional groups that
can confer novel properties such as antibac-
terial, antigenic and anticoagulant activities
(Lillo and Matsuhiro, 1997).
14.1.1
Chitosan, chitooligosaccharides
and derivatives
Chitosan presents biological activity owing
to its biocompatibility. This polysaccha-
ride is a cationic biopolymer obtained
by the N-deacetylation of chitin. These
polysaccharides are widely distributed in
the shells of crustacea (crab, shrimp, etc.),
in the cuticles of insects, in the shells and
skeletons of molluscs (krill, squid, etc.)
and in the cell walls of fungi (mushroom,
baker's yeast, etc.). The amino and two
hydroxyl groups found in chitosan are
* E-mail: llillo@ubiobio.cl
Search WWH ::
Custom Search