Modification of chitosan for simultaneous antioxidant and antibacterial functions

Abstract

Chitosan is a biocompatible polymer with antibacterial activity against a broad spectrum of bacteria while essential oils are known to possess antimicrobial and antioxidant activity. L-ascorbic acid is also popular as an antioxidant. In this thesis, chitosan was conferred with both antioxidant and antibacterial properties by grafting with eugenol, carvacrol and ascorbic acid, respectively. The surface concentration of the grafted essential oils and ascorbic acid was determined by X-ray photoelectron spectroscopy (XPS). The antioxidant activities of the carvacrol-grafted chitosan nanoparticles (CHCA NPs), the eugenol-grafted chitosan nanoparticles (CHEU NPs) and chitosan ascorbate (CHAA) were assayed with diphenylpicrylhydrazyl (DPPH). Antibacterial assays were carried out with a representative gram-negative bacterium, Escherichia coli (E. coli) and a gram-positive bacterium, Staphylococcus aureus (S. aureus). The grafted essential oils and ascorbic acid conferred antioxidant activity to the chitosan, and the essential oil-grafted chitosan nanoparticles achieved an antibacterial activity equivalent to or better than that of the unmodified chitosan nanoparticles. On the other hand, the antibacterial efficacy of CHAA decreased compared to that of pristine chitosan. Cytotoxicity assays using 3T3 mouse fibroblast showed that the cytotoxicity of CHEU NPs, CHCA NPs and CHAA were significant lower than those of the pure essential oils and ascorbic acid.