An experimental study was carried out on the production of β-glucans, a group of immuno-stimulating exopolysaccharides, by Agaricus blazei in submerged culture. The influences of seed condition, inoculmn size, pH, medium composition, and dissolved oxygen concentration (DOC) on exopolysaccharide production were investigated in flask and batch cultures. The temperature was 28 oC. Blending of seed culture broth to control the pellet size was found to have significant effects on initial cell growth and exopolysaccharide production. The optimum inoculum size and pH were 10 % (v/v) and 5, respectively. The optimal weight ratio of the two major carbon sources, glucose and dextrin was 1 : 4. The optimal weight ratio of the two major nitrogen ssources, yeast extract and soytone peptone was 2 : 1. The addition of 500 mg/L of MnSO4.5H2O slightly increased cell growth and exopolysaccharide production. The effects of DOC and DOC control methods on cell growth and exopolysaccharide production were investigated in a 7L bioreactor system. DOC showed no significant effects over 20 % of air saturation. When DO was controlled at about 20 % by manipulation of agitation speed, cell mass productivity and exopolysaccharide productivity were observed to increase by 41 % and 100 %, respectively, as compared to the control (cultures with no DO control). When DO was controlled at about 20 % by supply of pure oxygen at a fixed agitation speed, cell mass productivity and exopolysaccharide productivity were observed to be 42 % and 70 % higher, respectively, than the control. These results implied that an increased shear stress caused by more rigorous agitation speed as in the case of no oxygen supply could have positive effects. In order to overcome cell growth retardation at the end of batch fermentation and to maximize cell growth and exopolysaccharide production, two types of fed-batch operation modes, pH-stat and DO-stat cultures, were performed for various feeding medium compositions. When a feeding stock solution containing 45 % glucose, 6 % yeast extract and 3 % soytone peptone was added in a DO-stat culture, 37.10 g/L of maximum cell mass and 10.87 g/L of maximum exopolysaccharide concentration were obtained. The cell mass and exopolysaccharide productivities were 0.344 g/L-h and 0.101 g/L-h, respectively.
