Enzymatic modification of chitosan by cinnamic acids: Antibacterial activity against Ralstonia solanacearum

•Five chitosan derivatives with cinnamic acids (CTS-g-CADs) were synthesized.•IC50 of CTS-g-CA against mulberry bacterial wilt pathogen RS-5 was 2/5 of CTS.•3. IC50 of CTS-g-CADs against potato bacterial wilt pathogen GIM1.74 was 1/10 of CTS.

This study aimed to identify chitosan polymers that have antibacterial activity against the bacterial wilt pathogen. The chitosan polymers were enzymatically synthesized using chitosan and five cinnamic acids (CADs): caffeic acid (CA), ferulic acid (FA), cinnamic acid (CIA), p-coumaric acid (COA) and chlorogenic acid (CHA), using laccase from Pleurotus ostreatus as a catalyst. The reaction was performed in a phosphate buffered solution under heterogenous reaction conditions. The chitosan derivatives (CTS-g-CADs) were characterized by FT-IR, XRD, TGA and SEM. FT-IR demonstrated that the reaction products bound covalently to the free amino groups or hydroxyl groups of chitosan via band of amide I or ester band. XRD showed a reduced packing density for grafted chitosan comparing to original chitosan. TGA demonstrated that CTS-g-CADs have a higher thermostability than chitosan. Additionally, chitosan and its derivatives showed similar antibacterial activity. However, the IC50 value of the chitosan-caffeic acid derivative (CTS-g-CA) against the mulberry bacterial wilt pathogen RS-5 was 0.23 mg/mL, which was two-fifths of the IC50 value of chitosan. Therefore, the enzymatically synthesized chitosan polymers can be used to control plant diseases in biotechnological domains.

Graphical abstractFive chitosan derivatives that contain cinnamic acids (CTS-g-CADs) were successfully synthesized with laccase as a catalyst via band of amine I and ester band. Next, we evaluated the antibacterial activities of CTS, CTS-g-CADs and the initial CADs against Ralstonia solanacearum.Figure optionsDownload full-size imageDownload as PowerPoint slide