Biomedical Engineering Reference
In-Depth Information
and the energy of LPS binding with chitosans decreased with increase in
acetate group content in chitosans and resulted in changing of binding sites.
It was also observed that binding sites of chitooligosaccharides on LPS over-
lapped and chitooligosaccharide binding energies increased with increase
in number of monosaccharide residues in chitosan molecules.
6.4.2.3 pH
h e antimicrobial activity of chitosan is strongly af ected by pH [47, 58,
71]. h e antibacterial property is observed at acidic pH since at that pH,
chitosan will be protonated [80]. Tsai and Su examined the antimicrobial
activity of chitosan (DDA 0.98) against
E. coli
at dif erent pH values of 5.0,
6.0, 7.0, 8.0 and 9.0 [43]. h e greatest activity was observed at pH 5.0. h e
activity decreased as the pH increased, and chitosan had little antibacterial
activity at pH 9.0. Other researchers reported that chitosan had no anti-
microbial activity at pH 7.0 due to the deprotonation of amino groups and
poor solubility in water at pH 7 [43, 58].
6.4.2.4
Cations and Polyanions
Results regarding the ef ect of ionic strength on chitosan's antibacterial activ-
ity are still contradictory. While Chung,
et al.
[41], proposed that higher ionic
strength might enhance the solubility of chitosan and thus increase its anti-
bacterial activity, regardless of the test strain, Tsai and Su [43] suggested that
the presence of sodium ions (100 mM) reduced chitosan's activity against
E.
coli
. Raafat however, observed no detectable ef ect of NaCl (10 or 25 mM) on
the antimicrobial activity of chitosan against several indicator strains [81].
h e divalent cations at concentrations of 10 and 25 mM reduced the antibac-
terial activity of shrimp chitosan against
E. coli
in the order of Ba
2+
, Ca
2+
and
Mg
2+
[43]. Furthermore, the addition of Zn
2+
ions inhibited the antibacterial
activity of 0.2 M acetic acid-chitosan solution the most, compared to Ba
2+
,
Ca
2+
and Mg
2+
ions [41].
Analogous i ndings have been made for plant cells
(
Glycine max
), where chitosan-induced permeability changes were strongly
inhibited by divalent cations in the order Ba
2+
>Ca
2+
>Sr
2+
>Mg
2+
>Na+>K
+
[47]
It was assumed that the cations displaced Ca
2+
released from the cell sur-
face, form complexes stabilising the cell membrane and consequently reduce
the chitosan-induced leakage. However, Takanori,
et al
[80] and Chung,
et
al
[41]
claimed that the pH, rather than metal ion concentration, is more
important in antibacterial activity.
h e polyanions like Na-polygalacturonate and Na-poly-L-aspartate, but
not the monomeric galacturonate and aspartate, prevented the ef ect of
chitosan on plant cell. h e explanation of this provided was, that individual
