Degradation Of Chitosan By Radiation And The Antimicrobial Activity Of The Degraded Products

Chitosan is one kind of polysaccharides composed of glucoseamine and N-acetylglucosamine.Chitosan and its derivatives have a special set of interesting properities:nontoxicity,biocompatibility,controllable biodegradability,and nonantigenicity.These properities make chitosan an attractive biopolymer for applications in wide areas such as biotechnology,pharmaceuticals,wastewater treatment,agricultural,food science and other industries.In recent years,it has been reported that many properties of chitosan depend on the molecular weight,it has great discrepancy for chitosan with different molecular weight,some properities even on the contradiction.The previous studies demonstrated that the chitosan with an average molecular weight in the rangeof 10³-10⁴ Da is the most useful products,so it is a research spot to degradate the higher molecular weight of chitosan to satisfy the requirement of its various applications.The degradation of chitosan by ⁶⁰Co-γray irradiation in the solid state and synergetic degradation by irradiation and chemical agent were investigated in this paper.Four factors which affect the synergetic degradation of chitosan: irradiation dose,hydrogen peroxide concentration,the ratio of hydrogen peroxide and chitosan (volum/weight), acetic acid concentration were analyzed.The first three factors were measured by multiple comparisons of the different level and variance analysis.It is concluded that synergetic degradation is superior to degradation of chitosan by irradiation in the solid state.Chitosan's viscosity-average molecular weight was decreased from 8.7×10⁵ to 10⁴ at the condition of 15 % H₂O₂,HAc1.5%,4:1H₂O₂/chitosan,110kGy irradiation dose.Infrared sp(?)ctroscopy was applied to check the degradation products,and the chemical structure of degraded chitosan products changed slightly.Ring opening reaction caused by degradating chitosan with acetic acid is less than by improving the ratio of hydrogen peroxide and chitosan,besides of this,the redulting products has much lower average-molecular weight.The antimicrobial activities of chitosan products with different molecular weight against microorganisms were investigated,the results showed that,they have excellent antimicrobial activities of chitosan with the an average molecular weight in the range of 10⁴-10⁵DaThe best antimicrobial activities of chitosan against Escherichia coli, Staphylococcus aureus and Bacillus subtilis is 1.15×10⁴Da,1.021×10⁵ Da and 7.70×10⁴ Da respectively,the minimal inhibitory concentration is about 0.05%-0.1%.The best antimicrobial activities of chitosan against Aspergillus flavus is the chitosan sample with the molecular weight of 1.161×10⁵ Da and 7.19×10⁴Da, against Aspergillus niger is the chitosan sample with the molecular weight of 1.161×10⁵ Da and 2.76×10⁴,against penicillium is the chitosan sample with the molecular weight of 1.161×10⁵ Da and 3.21×10⁴Da,the minimal inhibitory concentration is about 0.1%-0.2%,a little higher than against bacteria.