Abstract: In this paper, chitosan (CTS) grafted copolymer with gallic acid (GA) was synthesized by laccase and horse radish peroxidase to enhance the antioxidant activity of chitosan. The effects of enzyme type and dosage, initial reaction pH, temperature, reaction time, and enzyme-to-substrate ratio on the grafting ratio were studied. The maximum grafting ratio (65.2%) was obtained when the reaction took place at 25 ℃ for 5 h in 100 mL of acetate buffer solution (100 mmol/L) at pH 4.5 with a mass ratio of GA to CTS of 3 in the presence of 4 U of laccase under constant stirring. At the same dosage, the CTSGA copolymer showed significantly higher antioxidant activity than chitosan and had no cytotoxicity.

Key words: enzyme, derivative from chitosan and gallic acid, antioxidant, cytotoxicity