| Chitosan which is biodegradable, biocompatible and biological nontoxic can inhibit microbes and is also considered as a kind of good materials for developing natural, safe food preservatives. Due to the antimicrobial activity is easily affected by the pH and solubility, chitosan cannot be widely used in food industry as a preservative. To improve the antimicrobial activity of chitosan and enlarge chitosan's pH range of application, we have used chitosan and benzoyl chloride to synthesize benzoyl chitosan ester. There will be high academic value for the development and application of chitosan as a preservative and its further processing.Using macromolecules of chitosan and N-Acetyl-D-Glucosamine(NAG) as raw materials and benzoyl chloride as acylating agent, we synthesised benzoyl chitosan ester and benzoyl NAG ester. Our research showed that when the reaction temperature was 0℃, the time was 3h (benzoyl chloride/glucosamine residues), the yield would be the highest. While when the molar ratio of reagents was 6:1, the substitution degree of benzoyl chitosan ester was 1.8, the yeild was 60%~70%. When the molar ratio of reagents was 4:1 (benzoyl chloride/NAG), the yeild of benzoyl NAG ester was 80%~85%.The chemical structure of the products were characterized by FT-IR, LC-MS. The solubility and thermal stability were also studied.The results showed that acylation occurred at the hydroxyl of chitosan. Benzoyl NAG triester accounted for 97%. The thermal decomposition temperature of benzoyl chitoan ester was 187~196℃and its thermal stability was better than chitosan. The thermal decomposition temperature of benzoyl NAG ester was 187~196℃and its thermal stability was worse than NAG.. In acetone, ethyl acetate and other organic solvents, they all had a good solubility.The antibacterial activity was conducted by inhibition zone and plate colony count method. The influencing factors were studied. We compared their inhibitory effect with benzoic acid, chitosan, NAG at different pH values. Also we preliminary analysised the relation between molecular structure and antimicrobial effect.The antibacterial activity increased with the concentration and changing pH values had little effect on their inhibitory effect.The inhibitory experiments showed that the two products had significant effect against the growth of microorganisms tested from pH3.5 to pH7.5.The minimum inhibitory concentration (MIC) of benzoyl chitosan ester against Escherichia coli, Staphylococcus aureus, Aspergillus niger, Saccharomyces cerevisiae were 0.02%~0.04%,0.20%~0.29%, 0.04%~0.10%,0.05%~0.07%. The MIC of benzoyl NAG ester against microorganisms tested were 0.24%~0.26%,0.14%~0.16%,0.20%~0.22%,0.18%~0.20%.The antibacterial effect incr- eased with increasing substitution degree of benzoyl chitosan ester.The inhibitory effect of benzoyl NAG ester against Escherichia coli was between benzoyl chitosan ester(D=0.5) and benzoyl chitosan ester (D=0.9),against Staphylococcus aureus was a little higher than benzoyl chitosan ester(D=1.8),against Aspergillus niger and Saccharomyces cerevisiae were the same as benzoyl chitosan ester(D=0.9).Our study showed that in acidic and neutral conditions, the two products both had good inhibition effect on microorganisms tested. They were expected to be developed into a low toxic, high efficient, broad antibacterial spectrum preservatives that could be widely used in food industry.
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