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

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. A chitosan-gentamicin derivative (CS-GT) was synthesized by introduction of gentamicin at C-6 hydroxyl group of chitosan. The introduction of gentamicin endowed CS-GT with more amino groups, resulting in improved water solubility and antibacterial activity. In addition, CS-GT coatings have been designed for food packaging. The obtained coatings exhibited appropriate appropriate physico-chemical performances. Thus, these CS-GT coatings can reduce the microbial erosion of litchis and papayas, thus, effectively delay the senescence of litchis and papayas and have broad prospects for applications in food packaging. [Display omitted] •A chitosan grafted with gentamicin (CS-GT) was successfully synthesized.•CS-GT has improved water solubility and antibacterial activity.•CS-GT coatings have appropriate physico-chemical performances.•CS-GT coatings can effectively delay the senescence of litchis and papayas.