Antimicrobial and inhibitory enzyme activity of N-(benzyl) and quaternary N-(benzyl) chitosan derivatives on plant pathogens

Chemical modification of a biopolymer chitosan by introducing quaternary ammonium moieties into the polymer backbone enhances its antimicrobial activity. In the present study, a series of quaternary N-(benzyl) chitosan derivatives were synthesized and characterized by 1H-NMR, FT-IR and UV spectroscopic techniques. The antimicrobial activity against crop-threatening bacteria Agrobacterium tumefaciens and Erwinia carotovora and fungi Botrytis cinerea, Botryodiplodia theobromae, Fusarium oxysporum and Phytophthora infestans were evaluated. The results proved that the grafting of benzyl moiety or quaternization of the derivatives onto chitosan molecule was successful in inhibiting the microbial growth. Moreover, increase water-solubility of the compounds by quaternization significantly increased the activity against bacteria and fungi. Exocellular enzymes including polygalacturonase (PGase), pectin-lyase (PLase), polyphenol oxidase (PPOase) and cellulase were also affected at 1000 mg/L. These compounds especially quaternary-based chitosan derivatives that have good inhibitory effect should be potentially used as antimicrobial agents in crop protection.