Antioxidant properties of chitosan from crab shells

Abstract

Crab chitosan was prepared by alkaline N-deacetylation of crab chitin for 60, 90 and 120 min and its antioxidant properties studied. Chitosan exhibited showed antioxidant activities of 58.3–70.2% at 1 mg/mL and showed reducing powers of 0.32–0.44 at 10 mg/mL. At 10 mg/mL, the scavenging ability of chitosan C60 on 1,1-diphenyl-2-picrylhydrazyl radicals was 28.4% whereas those of other chitosans were 46.4–52.3%. At 0.1 mg/mL, scavenging abilities on hydroxyl radicals were 62.3–77.6% whereas at 1 mg/mL, chelating abilities on ferrous ions were 82.9–96.5%. All EC₅₀ values of antioxidant activity were below 1.5 mg/mL. With regard to antioxidant properties assayed, the effectiveness of chitosans C60, C90 and C120 correlated with their N-deacetylation times. Overall, crab chitosan was good in antioxidant activity, scavenging ability on hydroxyl radicals and chelating abilities on ferrous ions and may be used as a source of antioxidants, as a possible food supplement or ingredient in the pharmaceutical industry.

Introduction

Chitin, found in the shell of crustaceans, the cuticles of insects, and the cell walls of fungi, is the second abundant biopolymer in the nature (Knorr, 1984). Structurally, chitin is a straight-chain polymer composed of β-1,4-N-acetylglucosamine and classified into α-, β- and γ-chitin (Cabib, 1981, Cabib et al., 1988). Chitosan derived by partial N-deacetylation of chitin is also a straight-chain polymer of glucosamine and N-acetylglucosamine (Muzzarelli, Rochetti, Stanic, & Weckx, 1997). α-Chitin, the most abundant in nature, has a structure of antiparallel chains and is found in the crab, shrimp and lobster whereas β-chitin found in squid has intrasheet hydrogen bonding by parallel chains (Jang et al., 2004, Minke and Blackwell, 1978). However, γ-chitin found in the cell walls of fungi has a mixture of parallel and antiparallel chains, which is a combination of α-chitin and β-chitin (Jang et al., 2004).

Because chitin and chitosan possesses many beneficially biological properties such as antimicrobial activity (Kobayashi et al., 1990, Tokoro et al., 1989), biocompatibility, biodegradability, hemostatic activity and woundhealing property, much attention has been paid to its biomedical applications (Farkas, 1990, Fleet and Phaff, 1981). Due to these unique properties, chitosan and its derivatives have been proposed for applications in biomedical, food, agriculture, biotechnology and pharmaceutical fields (Felse and Panda, 1999, Kumar, 2000, Shahidi et al., 1999).

Antioxidant properties of chitosan derivatives have been studied (Lin and Chou, 2004, Xie et al., 2001, Xing et al., 2005). Furthermore, antioxidant properties of fungal chitosan from shiitake stipes have also been studied (Yen, Tseng, Li, & Mau, 2007). However, antioxidant properties of chitosan derived from crab shells are not available. Accordingly, the objective of this study was to assess the antioxidant properties of chitosan prepared from crab chitin by N-deacetylation using a concentrated sodium hydroxide solution. Antioxidant properties assayed were antioxidant activity by the conjugated diene method, reducing power, scavenging abilities on radicals and chelating ability on ferrous ions.