Modification Of Chitin/Chitosan And Evaluation Of Their Antioxidant Activity And Antibacterial Activity In Vitro

Chitin/Chitosan is an inexhaustible renewable natural resource with a variety of unique features such as good hygroscopicity, film-forming activity, biocompatibility, biodegradability, lipid-lowering ability and antibacterial activitiy. However, the widespread application of chitin and chitosan are limited by their poor solubilities in neutral solvement. The aim of this study is to prepare water soluble chitin and chitosan derivatives and assess their antibacterial and antioxidant activity. Main conclusions are as follows:(1) The results of antioxidant and antibactierial activity of different viscosity chitosans showed that two unmodified chitosans exhibited certain antioxidant and antibacterial activities. Overall, the antioxidant and antibacerial capacity of the high viscosity chitosan(423mpa.s) was lower than the lower one(50mpa.s).(2) Quaternary amino groups were introduced into chitin and chitosan to obtain O-(2-hydroxy-3-trimethylammonium)propyl chitin(OHT-chitin) and N-(2-hydroxy-3-trimethylammonium)propyl chitosan (NHT-chitosan). Structural characterization were determined by IR spectiometer and GPC. The molecular weight(Mw)of OHT-chitin and NHT-chitosan were8986and9723with polydispersity of1.01and1.02, respectively.(3) The β-Carotene-linoleic acid activity, reducing power, scavenging activity of H2O2and DPPH assay were used to evaluate the antioxidant acticity of chitin and its derivatives. It was found that β-carotene-linoleic acid values of OHT-chitin and NHT-chitosan at0.6mg/mL were up to90%or more. The reducing power were1.192and0.576at5mg/mL. H2O2scavenging activity of NHT-chitosan and OHT-chitin were59.4%and56.3%at240min, respectively. It was also found that scavenging mechanisms towards DPPH radicals were different after modification. Both absorption bands(326nm and517nm) of DPPH ehtanol solution were declined by quatemized chitin/chitosan while CMC(carboxymethyl chitosan) mainly roled at326nm, unmodified CTS(chitosan) and WS-CTS(water-soluble chitosan) roled at517nm.(4) Comparison on scavenging mechanisms towards DPPH radicals of BHT, Vc and NHT-chitosan with the range of concentration indicated that NHT-chitosan demonstrated a different free radical scavenging mechanism from BHT and Vc. The absorbance decrease of DPPH absorption bands at326nm and517nm was accompanied by the concurrent absorption band at433nm which corresponded to the formation of DPPH photoproducts. New product was separated by high-performance liquid chromatography.(5) MIC of NHT-chitosan against E. coli, S. cholerae-suis, S. aureus and B. subtilis were5.12,10.24,10.24and2.56mg/mL respectively, and MBC were20.48,40.96,40.96and10.24mg/mL Moreover, MIC of OHT-chitin against E. coli, S. cholerae-suis, S. aureus were all20.48mg/mL. OHT-chitn exibited strongest antibacterial effect on B. subtilis with the MIC of2.56mg/mL.To further explore the antimicrobial activities of OHT-chitin and NHT-chitosan, the time-kill assays were conducted. OHT-chitin and NHT-chitosan exhibited strong lethal effects on test bacteria when the concentration of the tested achieved MBC, and100%bacterial death was observated within incubation for6h from the begnining of the treatments(total bacteria count approximately105cfu/mL).