Evaluation of antioxidant capacity of ulvan-like polymer obtained by regioselective oxidation of gellan exopolysaccharide Elboutachfaiti Redouan a,⇑ , Petit Emmanuel a , Pillon Michelle a , Courtois Bernard a , Courtois Josiane a , Delattre Cédric b a LPMV, Université de Picardie Jules Verne, Avenue des facultés, Le Bailly, F-80025 Amiens Cedex 1, France b GREENTECH Naturally, Biopôle Clermont Limagne, 63360 Saint Beauzire, France article info Article history: Received 20 September 2010 Received in revised form 14 November 2010 Accepted 18 January 2011 Available online 25 January 2011 Keywords: Antioxidant Gellan Regiospecific oxidation Rhamnoglucuronan Ulvan like abstract Gellan is an exopolysaccharide produced in high yield by the non-pathogenic bacterium Sphingomonas elodea ATCC 31461. In this study, four carboxylated derivatives of gellan (OG-1, OG-2, OG-3 and OG-4) with different uronics acid content were prepared using the TEMPO (nitroxyl radical 2,2,6,6-tetrameth- ylpiperidine-1-oxyl radical) mediated oxidation and their antioxidant activities were investigated includ- ing scavenging activity of hydroxyl, superoxide anion and 1,1-diphenyl-2-picryl-hydrazyl radicals. The results of chemical analysis and 13 C NMR spectrums indicated that the modification was successful. In addition, certain derivative exhibited stronger antioxidant activity compared to that of native ones. The high uronic acids derivative (OG-4) showed the most excellent antioxidant activity in three assays. These results suggested the potential of TEMPO-mediated oxidation in developing water-soluble antiox- idative polysaccharides from gellan still taking advantage of its low-cost production. The original carbo- hydrate structure of OG-4 derivative might find use as surrogates of ulvan, a cell-wall polysaccharides extracted from green seaweeds Ulva sp. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction A growing amount of research in biology and medicine has been devoted to reactive oxygen species (ROS). There now is consider- able evidence that highly reactive and charged ROS in the forms of superoxide anion ( Å O  2 ), hydroxyl radical ( Å OH) and hydrogen peroxide (H 2 O 2 ) can attack and induce oxidative damage in vital biomolecules such as DNA, lipids and proteins in cells and body flu- ids. This damage causes atherosclerosis, ageing, cancer, and several other diseases (Wang et al., 2009). Antioxidants, which scavenge free radicals, are known to play important roles in preventing ROS-induced diseases (Wade, Jackson, Highton, & van Rij, 1987). However, the commonly used synthetic antioxidants such as BHA (buthylated hydroxyanisole) and BHT (buthylated hydroxytoluene) are restricted by legislative rules because they are suspected to have some toxic effects and as possible carcinogens as well as gen- eral tendencies in consumer preferences towards naturalness of foods, there is a growing interest in natural antioxidants. Recently, there is a considerable interest in the food industry and in the preventive medicine for the development of antioxi- dants from natural sources, such as marine flora and fauna, bacte- ria, fungi and higher plants (Chattopadhyay et al., 2010). Among them, marine algae represent one of the richest sources of bioac- tive compounds. One particularly interesting feature of marine algae is their richness in sulphated polysaccharides. The uses of these biomacromolecules span from food, cosmetic and pharma- ceutical industries to microbiology and biotechnology (Chattopad- hyay et al., 2010). In recent years, several classes of sulphated polysaccharides have been demonstrated to show antioxidant activity, too. The com- pounds tested included ulvan from marine green algae Ulva sp., mainly composed of rhamnose, xylose, glucuronic acid, iduronic acid, and sulphate, with smaller amounts of glucose, mannose, arab- inose, and galactose. The mainly repeating disaccharide units are [b-D-GlcpA-(1 ? 4)-a-L-Rhap 3s] and [L-IdopA-(1 ? 4)-a-L-Rhap 3s] (Lahaye & Robic, 2007). These sulphated rhamnoglycuronan poly- mer have been demonstrated to play an important role as free radical scavengers in vitro and antioxidants for the prevention of oxidative damage in living organisms (Qi & Zhang et al., 2005). Their activity depends on several structural parameters such as the degree of sul- phation (DS), the molecular weight and type of sugar (Qi et al., 2005; Qi & Zhao et al., 2005). Usually, ulvan is extracted from green sea- weeds Ulva sp. using hot water often containing a calcium chelating agent such as sodium oxalate (Elboutachfaiti et al., 2009; Lahaye & Robic, 2007). Nevertheless, under these extraction conditions, the chemical structure can varies according to (i) its period of collect, (ii) the seaweed species, and (iii) all the post-collect treatment 0308-8146/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2011.01.067 ⇑ Corresponding author. Tel.: +33 3 2253494; fax: +33 3 22956254. E-mail address: redouan_elboutachfaiti@hotmail.com (E. Redouan). Food Chemistry 127 (2011) 976–983 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem