Effect of molecular weight of chitosans on their antioxidative activities in apple juice

This work studies how chitosans with low molecular weight (LMWC, M-w=12 kDa), medium molecular weight (MMWC, M-w=95 kDa) and high molecular weight (HMWC, M-w=318 kDa) affect antioxidant activity in an aqueous system and in apple juice. Antioxidant activity was determined, including that of DPPH radicals, hydrogen peroxide and superoxide anion radicals, as well as metal ion chelating capacity, ABTS radicals of chitosans with different molecular weights (DMWCs) in apple juice. LMWC exhibited stronger scavenging activity toward DPPH radicals, superoxide anion radicals and hydrogen peroxide, compared to either MMWC or HMWC. At a concentration of 0.8 mg/ml, the LMWC in apple juice exhibited 88.2%, 99.8% and 93.0% scavenging activities toward DPPH radicals, hydrogen peroxide and superoxide anion radicals, respectively. At a concentration of 1.0 mg/ml the LMWC in apple juice exhibited 70.0% ferrous ion chelating activity. The TEAC (Trolox Equivalent Antioxidant Capacity) values of LMWC (3.24 +/- 0.21) were markedly higher than those of HMWC (1.75 +/- 0.12) in apple juice. The data obtained in vitro models clearly establish the antioxidant potency of DMWCs. These in vitro results suggested that LMWC can increase antioxidant activity in apple juice. However, comprehensive studies need to be conducted to ascertain the in vivo safety of LMWC in experimental animal models. (c) 2006 Elsevier Ltd. All rights reserved.