In the present study, a critical effect of aeration on the production of exopolysaccharides (EPS) and their quality was described. The maximum production of EPS (2.36 g l(-1)) and mycelial biomass (21.56 g l(-1)) were achieved at a high aeration rate of 3.5 vvm. There was a significant variance in the morphology between different aeration conditions: loose mycelial clumps developed and their size and hairiness increased as the aeration rate increased from 0.5 to 3.5 vvm, increasing the apparent viscosity of the broth. The three EPS groups (designated as Fr-I, Fr-II, and Fr-III) were fractionated from the culture filtrates by a gel filtration chromatography on Sepharose CL-6B and their molecular weights were estimated to be 1820, 14-45.4, and 1.8-1.9 kDa, respectively. The compositional analysis revealed that all three EPS groups were proteoglycans consisting of 76.6-84.4% carbohydrates and 15.6-23.4% proteins. The group Fr-III had the same molecular weight and similar chemical composition, whereas the groups Fr-I and Fr-II showed quite different chemical compositions while produced by varying the aeration conditions. (C) 2004 Elsevier Inc. All rights reserved.