Improvement of antioxidant activity of chitosan by chemical treatment and ionizing radiation

► We modified chitosan to N-maleoylchitosan, N-phthaloylchitosan and sulfonated chitosan. ► We examined changes upon effect of γ-rays on chitosan and its derivatives. ► We evaluated the antioxidant activity of chitosan derivatives using different methods. ► Irradiation of chitosan and its derivatives enhance their antioxidant activities. ► Chitosan and its derivatives could be used as natural antioxidants.