Research Of Preparation And Antibacterial Properties Of Chitosan Derivatives

Chitosan (CS), as a kind of alkaline polysaccharides, is essentially deacetylated chitin. Chitosan has broad spectra of antibacterial properties with a lot of application in industrials. However, high molecular weight (MW) chitosan can only be dissolved in acid solution rather than in alkaline solution. This characteristic is limiting the application of this material to a great extent. For the aim of improving the dissolubility of chitosan, many kinds of its derivatives have been synthesized and prepared. But from the state-of-art review, there is hardly viable preparation method that can directly put into processing practice. The disadvantages of the current methods are poor stability and yield of the product, complicated process, as well as overlong reaction time. Thus, to improve the preparation method and study the antimicrobial activity of water-soluble chitosan derivative are attracting more attention.Chitosan (MW 1800 KDa, Degree of deacetylation, DD 86%) is selected as the raw material. Alkyd degradation method has been employed to prepare different kinds of low MW chitosan. The MW of the low MW product is 1180KDa, 260KDa and 94KDa, respectively. Along with the reaction time, the MW drops but the DD value remains the same in the degradation process. The DD of different products are the same, 86±0.5%. The FTIR spectra analysis and DD value determination suggested that, only the glycosidic bond breaks in the degradation process. The amido bonds remain intact after chitosan is degraded. The feature is important that can guarantee the stability of the chitosan as raw material.The chitosan material is swelling and surface-modified. Then Chitosan acetate (CA) is prepared using the different MW CS above. The newly produced product is faint yellow powder, soluble in water and acid solution and insoluble in alkaline solution. The OD420 value of the product dissolved in water is 0.022 with a pH range from 4.91 to 5.01. In this research, the input-output ratio of different MW CA is 5:9 (CA_a), 5:8(CA_b) and 5:8 (CA_c), respectively. Using the designed substituted ratio test method, the ratio is 39.6±1.2% (CA_a), 38.5±1.5% (CA_b) and 39.6±1.1% (CA_c), respectively. FTIR spectra of CA indicate the binding site is ionic bond forming a–NH3+.RCOO- structure. After sealed in a bag for 180 d, the characteristics of CA are still similar to that of newly produced product.Three kinds of Hydroxypropyl Trimethyl ammonium chloride chitosan (HACC) of named HACCa,HACCb,HACCc are prepared from the different MW CS using the improved method described above. Bending vibration absorption is found at 1490cm-1 in the FTIR spectra which indicates the Epoxy propyl trimethyl ammonium chloride (EPTAC) has been successfully introduced on forming covalent bonds with a–NH2?RN+(CH3)3Cl- structure. The newly produced HACC is yellowish powder, soluble in neutral, acidic and alkaline solution. The OD420 value of the product dissolved in water is 0.090 with a pH range from 6.60 to 6.71. The input-output ratio of different MW HACC is 30:59(HACCa), 15:29 (HACCb ) and 15:29 (HACCc), respectively. Substituted ratio of the product is 91.3±0.2% (HACCa), 91.7±0.3% (HACCb) and 91.6±0.2% (HACCc). After sealed in a bag for 180 d, the characteristics of HACC are still similar to that of newly produced product.E. coli and S. aureu have been introduced in the antimicrobial activity determination. Turbidimetric analysis and spread plate method have been employed to maintain the accuracy in the test. In the Turbidimetric analysis, the antimicrobial activity rises along with the concentrations of the CA and HACC. When the concentration is lower than 0.05%(w/v), no obvious antimicrobial activity is found while it reaches 0.1%(w/v), high antimicrobial activity can be achieved. Under the same concentration, the two derivatives have better prohibitive effect on S.aureu than E.coli. Besides, the HACC performs better than CA. The high MW CS derivative is more effective to E.coli while the low MW CS derivative is more effective to S.aureu.In the spread plate method test, different MW CA and HACC has similarities of the Turbidimetric test results when used at the same concentration: when the concentration reaches 0.1%(w/v), they are both effective to E. coli and S. aureu. No visible colony can be found in the microscopic examination. For the Contrast bacteriostatic experiment, CA and HACC have been introduced in a comparison with Potassium Sorbate (PS). The result indicate that the antimicrobial activities of CS derivatives are similar to the PS in solution at given concentrations. Besides, the HACC performs better than CA as a mould inhibitor. When applied for the same period, soak processing has better effect than spray treatment. The feasibility of CS derivatives using as biopreservatives is proved by the research. These derivatives have promising and hopeful development as a new type of biopreservative.