Synthesis Of Chitosan Derivatives And Analysis Of Their Antibacterial Activities

Chitosan is a renewable resource and exhibits unique characteristics, including biodegradability, biocompatibility, antioxidant activity and actibacterial activity. However, chitosan is only able to dissolve in some dilute acid solutions due to its inter- and intramolecular hydrogen-bonding network. This reduced solubility greatly limits its applications. In recent years, enzymatic method has many advantages in the synthesis of chitosan derivatives with high-activity, efficient reaction process and low content. Therefore, enzymatic method was used to synthesize novel chitosan derivatives, which have antibacterial activities to Ralstonia solanacearum and the preservation effect of mulberry fruit. The main research results are as follows:Chitosan and five kinds of phenolic acids were used as the substrates, and laccase was used as a catalyst to synthesize novel chitosan derivatives, and evaluate the antibacterial activity to Ralstonia solanacearum. The chitosan derivatives have band of amide I or ester band at 1670 cm-1 and 1700 cm-1. They also have a reduced packing density and higher thermostability than chitosan. IC50 of CTS-g-CA against mulberry bacterial wilt pathogen RS-5 was 2/5 of chitosan, and IC50 of chitosan derivatives against potato bacterial wilt pathogen GIM1.74 was 1/10 of chitosan. These results suggest that the antibacterial activities of chitosan derivatives improved when compare with chitosan.The fluorescence quantitative PCR was first used to detect the antibacterial activity of chitosan derivatives against mulberry bacterial wilt pathogen RS-5. While log(CFU/mL from 104 to 108) versus Ct was y=-3.193x+44.44(R2=0.9998). When the concentration of chitosan derivatives were 2.0 mg/mL, the concentration of bacterium decreased above 70%. These results suggested that qPCR could relect the antibacterial activities of chitosan derivatives against RS-5 by concentration of bacterium directly.CTS-g-CA was first used to preserve the quality and extend the shelf life of mulberry fruit. The co-toxicity factor of CA+CTS and CTS-g-CA were 12.91 and 52.99, respectively. Results suggested that CA+CTS showed an additive effect, and CTS-g-CA showed a synergistic effect in preserving mulberry fruit. On day 18, the rotting rate of CTS-g-CA treated mulberry fruit was only 37.67% when compared with that of the control at 97.67%. At the same time, CTS-g-CA could also maintain higher main active substances than other treatments. Therefore, CTS-g-CA is a novel preservative.In conclusion, five kinds of chitosan derivatives were successfully synthesized in this paper, which were used to research the antibacterial activities to Ralstonia solanacearum and the preservation effect of mulberry fruit. The qPCR method was built to detect the antibacterial activity of chitosan derivatives against mulberry bacterial wilt pathogen RS-5 fastly and directly. These methods provide potential support to control Ralstonia solanacearum and preserve mulberry fruit.