Degradation Of Chitosan And Its Antimicrobial Activity, Resistance To Oxidation

Chitosan is rich in resources and can be produced by crabs waste. Industrial production of chitosan can bring enormous economic, social and ecological benefit if we strengthen the research and development of its derivatives. Low-molecular-weight chitosan were prepared with oxide degradation by using hydrogen peroxide. The structure of degradation products were identified with FT-IR infrared spectroscopy. The reaction kinetics of the oxidative degradation was researched, and their antibacterial activity and antioxidant activity were studied systematically in this thesis. The copper(Ⅱ)and zinc(Ⅱ) complexes of chitosan and its degradation productions were prepared. Compared antioxidation of the complexes and ligand. It was established that the foundations for study and apply for the future.The main contents and conclusions of the thesis are as follows:(1)High-molecular-weight chitosan degraded by hydrogen peroxide in the unhomegeneous phase. The structure of degradation products were identified with FT-IR infrared spectroscopy. Investigated the influence of the degradation temperature(T), degradation time(t) and concentration of hydrogen peroxide(C). The significant effects of the three factors were also discussed. Three affecting factors were selected to study the preparation technology of chitosan degration solution. The results showed that the oxidative degradation products had the same structure with chitosan. The significant effect of three factors on the degree of deacetylation (DD) was: T>t>C; the significant effect on the intrinsic viscosity(η) was: T>C>t; the significant effect on the molecular weight(M) was: T>C>t . Optimum technological condition is C2A3B2, that is, the degradation time is 60min, the degradation temperature is 60℃, the concentration of hydrogen peroxide is 10%.(2)The reaction kinetics of chitosan during oxide degradation by hydrogen peroxide in the simple unhomegeneous phase were investigated. The results showed that the oxide degradation accorded with the dynamic theory of random degradation. The reaction of oxidative degradation is first order reaction and the activation energy is 27.97KJ.mol-1. Ihe rate constant(k) increased with increasing of the temperature.(3) The antimicrobial activities of chitosan and its degradation productions on Staphylococcus aureus, Escherichia coli, Bacillus subtilis, S.cerevisiae, Penicillium notatum and Aspergillus nige were studied. The relationship between antibacterial activity and the molecular weight, concentration, pH value, cultivation time were studied, and the minimum inhibitory concentration (MIC) of chitosan with different molecular weights were studied. The main conclusions are as follows: the antimicrobial efficiency increased with the molecular weight reducing. The antibacteral effect with bacteria is better than that with fungi. Staphylococcus aureus has highest sensitivity to chitosans among the three kinds of bacteria. As a whole, the antimicrobial efficiency of chitosan is: Staphylococcus aureus > Escherichia coli > Bacillus subtilis > S.cerevisiae > Penicillium sp. > Aspergillus niger; chitosan has the most significant antimicrobial efficiency in the pH value of 6.0-6.5; chitosan has the same antimicrobial efficiency with potassium sorbate and sodium benzoate when the viscosity- average molecular weight decreased to 10,400.(4)The antioxidant activity of chitosan and its degradation productions on superoxide anion (O2-·), hydroxyl radical (·OH) and hydrogen peroxide (H2O2) were studied preliminary. The copper(Ⅱ) and zinc(Ⅱ) complexes of chitosan and its degradation productions were prepared, compared the antioxidation of the complexes and ligand. The results showed that the complexes of chitosan and its degradation productions with copper(Ⅱ) and zinc(Ⅱ) had excellent antioxidant activity. It was proved that the intrduction of metal copper(Ⅱ) and zinc(Ⅱ) enhanced antioxidant activity of these complexes. The antioxidant activity of six samples was: LCTS-Cu(Ⅱ) > HCTS-Cu(Ⅱ) > LCTS-Zn(Ⅱ) > HCTS-Zn(Ⅱ)> LCTS > HCTS; the scavenging capacity of chitosan and its complexes with copper(Ⅱ) and zinc(Ⅱ) to O2-·,·OH and H2O2 are similar, and have the similar rule that the scavenging capacity increased with the concentration reduced in a certain range. As a whole, the result is H2O2 < O2-·<·OH.