Preparation and characterization of hydroxypropyl chitosan modified with nisin

Nisin had been grafted to hydroxypropyl chitosan (HPCS) using microbial transglutaminase (MTGase) as biocatalyst. HPCS was synthesized from chitosan and propylene oxide under alkali condition. The chemical structures of derivatives were characterized by FT-IR and ¹H NMR spectroscopy. The process conditions were optimized from the aspects of the reaction time, the reaction temperature, the molar ratio of nisin to HPCS and the mass ratio of MTGase to HPCS. In this study, the results of moisture absorption and retention tests showed HPCS-nisin had moisture absorption and moisture retention abilities. In addition, in vitro antibacterial activity assessment, HPCS-nisin with the concentration of 0.008mg/mL showed pronounced inhibitory effect against Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli). Furthermore, the methyl thiazolyl tetrazolium assay (MTT) was applied to evaluate the biocompatibility of HPCS-nisin, and the result indicated that HPCS-nisin with the degree of substitution (DS) of 0.18 displayed pronounced cell viability at 500ppm in the range of certain toxicity. Therefore, the results suggest that HPCS-nisin could be potential wound dressings for pharmaceutical applications.