Research On Preservatives And Antimicrobials Derived From Chitosan

Along with rising of people's living standard, it was widely concerned to develop natural, high-performance, safe and broad-spectrum antimicrobial agents. Due to its biodegradability, biocompatibility,non-toxicity and antimicrobial activity, how chitosan to be developed into natural antimicrobial agents has become one of hot research topics.The chemical active sites of chitosan were chemically modified to improve its solubility and to increase its antimicrobial activity. Three types of new chitosan derivatives including chitosan salts, chitosan derivatives bearing double antimicrobial functional groups and chitosan p-hydroxybenzoate were synthesized. The synthesis route, properties and antimicrobial activities of the chitosan derivatives were also discussed.In order to improve chitosan's solubility in water, salts of chitosan with organic acids were manufactured. By determining the solubility of chitosan in kinds of organic acid solutions, lactic acid was proved to be a best salting-forming agent. When chitosan was thoroughly soluble in lactic acid solution, its degree of protonation could be about 0.55 and [CH3CH(OH)COOH]/[Chit-NH2]=0.6. The chitosan lactate made under the conditions did not contain excess lactic acid. The content of lactic acid in chitosan lactate could accurately determined by potentiometric method, and the recovery of the method was 100.2%. The method could be used as a way to judge how excess of lactic acid was used in chitosan lactate.DSC curve showed that the chitosan lactate was heat-stability. Solubility test showed chitosan lactate was able to dissolve rapidly in natural water (in about 0.5-1.0h). The MICs of chitosan lactate against S. aurueus and E. coli were 0.05% and 0.1% respectively. The chitosan lactate could be applied in food system as a preservative.In order to increase its antimicrobial activity, chitosan was modified by introduced antimicrobial functional groups to hydroxyl and amino groups of chitosan.Through formation of schiff base, reduction, N-methylation and O–quaterisation, series of chitosan derivatives bearing single-antimicrobial functional group and bearing double antimicrobial functional groups had been synthesized, mainly including O-quaternized-N-alkyl-chitosans, O-quaternized-N-alkyl-bimethyl ammonium chitosans chloride and O-quaternized–N-chitosan schiff bases. Solubility test showed that these quaternized products were excellent solubility in water. FTIR, element analysis,1H NMR and degree of quaternization confirmed that derivation reactions had taken place. Solubility test showed that chitosan derivatives bearing functional group behaved better solubility in water than chitosan.