Applications of chitosan (CS) are hindered by its weak antimicrobial ability, poor solubility in basic and neutral solutions, structural modification is needed to improve its functional properties. Herein, a new chitosan-gentamicin derivative (CS-GT) was successfully synthesized via protection, regioselective bromination, nucleophile substitution reaction, and deprotection. Characterization techniques confirmed the successful introduction of GT onto the C-6 position of CS with a grafting rate of 76.19%. The additional amino groups provided by GT decreased the crystallinity and thermal stability of CS-GT, while enhancing its solubility in neutral and alkaline solutions. Compared to CS, CS-GT exhibited 2.50 and 2.41 times higher antibacterial activities against Escherichia coli and Staphylococcus aureus, respectively. Besides, an active packaging coating was develop by incorporating glycerol into CS-GT. The hydrogen bond networks formed within coatings endowed them good thermal stability and tightly uniform morphology. Furthermore, increasing CS-GT from 1% to 3% improved the coating's ultraviolet resistance and flexibility, but reduced its waterproof performance, visual appearance, and water barrier properties. Preservation experiments with papaya and litchi showed that CS-GT coatings effectively inhibited microbial growth and maintained quality and appearance up to 16 and 8 days of storage, respectively. In conclusion, CS-GT show promising potential for applications in food packaging.

Preparation and characterization of a chitosan-gentamicin derivative and its effect on tropical fruit preservation