An exopolysaccharide (EPS) with a molecular weight of 230 kDa, was isolated from Bordetella sp. B4. The EPS was identified as linear alpha-1,6-(6-methyl)glucan with N-acetyl-D-glucosamine branches at alpha-1, 4-linkages by IR and NMR spectroscopy. The free radical scavenging capacities of EPS on 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS(center dot+)), H2O2, -OH and lipid peroxidation were 2-, 86-, 134- and 18-fold higher than that of ascorbic acid, respectively. Compared with ascorbic acid, the EPS was more effective in preventing DNA and protein from free radical damage induced by 2,2'-azobis (2-amidinopropane) dihydrochloride (MPH). More significantly, the EPS did not degrade DNA and protein by the pro-oxidant effect in the presence of copper ions and H2O2. Furthermore, EPS could protect human umbilical vein endothelium cells (HUVECs) from high glucose-mediated damage. The production of EPS reached 10.2 g/L in the fermentation medium containing 3.0 g/L cholesterol, suggesting that Bordetella sp. B4 was a potential producer of antioxidant EPS. (C) 2012 Elsevier Ltd. All rights reserved.