Enhancement of antioxidant activity of chitosan by irradiation

Chitosan was irradiated in acetic acid solution (1%) with different doses (2-20 kGy) of Co-60 gamma rays to investigate the enhancement of antioxidant activity of irradiated chitosan. The structure of irradiation degraded chitosan was characterized by GPC, FT-IR and H-1 NMR spectroscopy. The molecular weight of chitosan decreased with increasing irradiation dose. Radical mediated lipid peroxidation inhibition, reducing power, superoxide anion radical and hydroxyl radical quenching assays were used for the evaluation of the antioxidant activity of irradiated chitosan. Chitosan (M-w 2.1 x 10(3)) which had been irradiated at 20 kGy exhibited high reductive capacity and expressed good inhibition of linoleic acid peroxidation. At a concentrtion of 0.1 mg/mL it could scavenge 74.2% of superoxide radical. At 2.5 mg/mL, scavenging percentage of chitosan irradiated for 0, 2, 10, 20 kGy against hydroxyl radical was 16.6%, 41.1%, 47.1% and 63.8%, respectively. The results show that gamma ray irradiation, especially for 20 kGy, of chitosan gives enough degradation to increase its antioxidant activity as a result of a change in molecular weight. (C) 2007 Elsevier Ltd. All rights reserved.