Enzymatic grafting of gallate ester onto chitosan: evaluation of antioxidant and antibacterial activities

Summary The antioxidant octyl gallate ( OG ) has been successfully grafted onto chitosan by means of horseradish peroxidase biocatalyst. The maximum gallate incorporation onto chitosan determined by 1 H NMR spectroscopy was up to 16 molar%. The resulting materials displayed antioxidant capacities with DPPH radical inhibition percentage up to 23% upon the assay conditions. The grafting of the antioxidant on chitosan enhanced its antimicrobial activity. Minimal inhibitory concentration ( MIC ) for E scherichia coli was 0.5 g L −1 . The native medium molecular weight chitosan alone or grafted with the lowest OG incorporation (ca. 11 molar%) attained 100% inhibition of E . coli , whereas lower inhibition was observed for all other materials 50.7–68.9% corresponding a reduction in the counts from 10.6 to 5.23–3.30 Log CFU mL −1 . The inhibition of L isteria monocytogenes was significantly higher (59.8–100%) than that with the G ram negative bacterium reaching the MIC at 0.25 g L −1 with a reduction in the counts from 12.6 Log CFU mL −1 to 5.06–0 Log CFU mL −1 .