Chemical characteristics and antioxidant activity of exopolysaccharide fractions from Microbacterium terregens Mohsen Mohamed Selim Asker a, * , Youssri Mohamed Ahmed a , Mohamed Fawzy Ramadan b a Microbial Biotechnology Department, National Research Center, El-Bohoss St., Dokki 12622, Cairo, Egypt b Biochemistry Department, Faculty of Agriculture, Zagazig University, Zagazig 44511, Egypt article info Article history: Received 23 October 2008 Received in revised form 12 January 2009 Accepted 26 January 2009 Available online 13 February 2009 Keywords: Microbacterium terregens Exopolysaccharide Isolation Purification Structure features GC–MS IR DPPH Antioxidant activity abstract The Gram-positive bacterial strain isolated from soil was identified as the non-pathogenic Microbacterium terregens. The exopolysaccharide (CPS) produced from M. terregens was obtained by isopropanol precip- itation (13.72 g L 1 growth medium), The resulted exopolysaccharide was purified by chromatography on DEAE-cellulose and Sephacryl S-200 columns, when two polysaccharide fractions termed CPSI and CPSII were obtained. Structure features of CPSI and CPSII were investigated by a combination of chemical and chromatographic analyses, such as acid hydrolysis, methylation analysis, periodate oxidation–Smith deg- radation, HPLC, GC–MS, and IR. The results indicated that CPSI and CPSII were composed of glucose: man- nose in a ratio of 2.7:1 and 3.2:1 with molecular weights 80 and 150 kDa, respectively. It has a backbone of (1 ? 4)-linked b-glucose residues, which occasionally branches at O-6. The branches were composed of (1 ? 4)-linked b-mannose residues. The antioxidant activity of the CPS, CPSI and CPSII was evaluated in-vitro by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay (RSA). CPSI fraction showed the highest antioxidant activity among the three fractions, with an IC 50 value of 230 lg mL 1 . The effect of molecular weight of the polysaccharide on the improvement of the antioxidant potential seems to be significant. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Exopolysaccharides represent a class of high-value polymers with many industrial applications in food, cosmetic, textile and pharmaceutical industries due to their rheological properties. They have been used as emulsifiers, as stabilizers and as texture en- hances in food industry. Traditionally, these important polysaccha- rides have been obtained from plant or algae sources. However, in the last years, new gums from cultivable microbial sources have been received increase attention. Thus, anionic extracellular poly- saccharides have been recovered from different bacteria such as Klebsiella pneumoniae (Kang, Veder, & Cottrell, 1983), Pseudomonas sp. (Williams & Winpenng, 1977) and Arthrobacter viscosus (Slaneker, Orentas, Knutsen, Watson, & Jeanes, 1968), as well as basidiomycetes such as Agricus sp., Oudemansiella conarri (Maziero, Cavazzoni, & Bononi, 1999) and Schizophyllum commune (Brever, 1991). However, the only extracellular polysaccharides that have been produced on a commercial scale are dextran and xanthan. On the other side, polysaccharides have been demonstrated to play important role as dietary free radical scavenger for the prevention of oxidative damage. There are increasing evidence indicating that reactive oxygen species produced by sunlight, ultraviolet light, ion- izing radiation, chemical reactions and metabolic processes have a wide variety of pathological effects, such as causing DNA damage, carcinogenesis and cellular degeneration related to aging (Blennder, Oliveira, Conboy, Haigis, & Guarente, 2003; Haran, 1993; Liu, Ooi, & Chang, 1997). In recent years, many studies have shown that reactive oxygen species (ROS) is responsible for various diseases such as cancer, Alzheimer’s diseases, Parkinson’s diseases, epilepsy, inflammation, retrolental fibroplasias, atherosclerosis, lung injury, ischemia-reperfusion injury and other disorders (Raouf, Patrice, Andre, Jean-Michel, & Yvan, 2000). Although almost all organisms possess antioxidant defense and repair systems that have evolved to protect them against oxidative damage, these sys- tems are insufficient to entirely prevent the damage. Against this background, natural antioxidants play an important role in the pre- vention of these diseases. Because many of synthetic antioxidants such as butylated hydroxyanisole and butylated hydroxytoluene used in foods are suspected to have cytotoxicity (Valentao et al., 2002), more attention has been paid to natural non-toxic antioxi- dants. In recent years, an increasing amount of evidence highlights that some polysaccharides isolated from plants, herbs and fungi had antioxidant activities and low cytotoxicity (Liu et al., 1997). The preliminary research showed that Misgurnus anguillicaudatus polysaccharide was able to remove O  2 , HO  ,H 2 O 2 and other active compounds of oxygen and significantly protected DNA chains from 0144-8617/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2009.01.037 * Corresponding author. Tel.: +2 02 33335982/01 29552825; fax: +2 02 333371931. E-mail address: mohsenmsa@yahoo.com (M.M.S. Asker). Carbohydrate Polymers 77 (2009) 563–567 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol