Evaluation On The Antibacterial Activities Of Chitosan And Its Derivatives

In this paper, chitosan (CTS, M_η: 4.7×10~5, DD: 85%) was degraded by hydrogen peroxide to nine products with different molecular weight (M_η: 4.7×10~5～8.0×10~4 ) and different degree of deacetylation (DD: 85%～100%). Solid plate method was used to estimate the antibacterial activities of all the chitosan samples for the gram-positive staphylococcus aureus and the gram-negative escherichia coli; the molecular weight, degree of deacetylation and the bacteria tested were reviewed, which would had effects on the antibacterial activities of chitosan. In order to overcome the highly strong intramolecular hydrogen bond between chitosan to increase its solubility in water, the modification was carried out to the amido and the hydroxy of chitosan. So hydroxypropyl chitosan (HP-CTS), O-carboxymethyl chitosan (O-CMCTS), N,O-carboxymethyl chitosan (N,O-CMCTS) and N-succinyl-chitosan (N-Suc-CTS) were prepared and the antibacterial activities of these derivatives for the staphylococcus aureus and the escherichia coli were studied. Effects on chitosan's antibacterial activities of the introduced function group and the molecular weight's change were also analyzed. CTS/PLA blended film with different scale were prepared by an emulsion blending technique, and ice acetic acid was firstly used as cosolvent to prepare the homogeneous CTS/PHB blended film with different scale. The film structure and the surface topography of these films were characterized and bacteriostatic circle method was used to test the antibacterial activities of the two kinds of films with different scale for E. coli and St. aureus. The research conclusions were as follows:When the concentration of chitosan was up to 1.0 g/L, its antibacterial activities for the two bacteria would be up to 100%. And the antibacterial activities of chitosan with the molecular weight of 8.0×10~4～2.5×10~3 for the gram-negative E. coli increased with increasing molecular weight. But when the molecular weight was less than 4.0×10~5, with the chitosan's molecular weight increased, the antibacterial activities for the St. aureus rose up at first and then decreased.The amido content of chitosan had a more interesting effect on the antibacterial activities for E. coli, compared to the change of molecular weight. But the factor of molecular weight played an more important role on the antibacterial activities for the St. aureus.The water-solubility of N,O-CMCTS, O-CMCTS, HP-CTS and N-Suc-CTS had highly been improved and, to some extent, the antibacterial activities of the chitosan was also improved, which had greatly expended the application of the chitosan. The introduced carboxyl group had highly improved the antibacterial activities of the chitosan, but the introduced hydroxypropyl didn't have an interesting effect on it.Compared to chitosan, HP-CTS, N-Suc-CTS and O-CMCTS exhibited an more excellent effect of moisture absorption and moisture retention.CTS/PLA blended film with different scale were prepared by an emulsion blending technique, and it was proved that the film was prepared by simplely blending CTS with PLA.Both of the two films were used for inhibiting bacterial, and it was found that the blended films had some antibacterial activities for E. coli and St. aureus. Especially, blended film had more antibacterial activeties if CTS content was higher.