RESUMEN
Polysaccharides, such as barley flour, dextrin and soluble starch, were better carbon sources than monosaccharides and disaccharides, such as glucose and maltose, for cell growth of Bacillus subtilis ZJF-1A5 and beta-glucanase production. beta-Glucanase produced by B. subtilis ZJF-1A5 was associated partially with cell growth and increased significantly when cells entered stationary phase; yeast extract was the best nitrogen source, followed by soybean flour. All inorganic nitrogen sources chosen in the experiments were not favorable for cell growth and enzyme production. A fractional factorial design (2(6-2)) was applied to elucidate medium components that significantly affect beta-glucanase production. The concentration of barley flour, corn flour and soybean flour in medium were significant factors. The steepest ascent method was used to locate the optimal domain and a central composite design was used to estimate the quadratic response surface from which the factor levels for maximum production of beta-glucanase were determined. The composition of fermentation medium optimized with response surface methodology was (g/l): barley flour, 63.5; corn flour, 44.8; KH2PO4, 1.0; MgSO4 x 7H2O, 0.1; CaCl2, 0.1. beta-Glucanase activity was 251 U/ml at 48 h using optimized medium, 1.4 times higher than that in original medium.