OPTIMIZATION OF ACETONE-BUTANOL PRODUCTION USING RESPONSE-SURFACE METHODOLOGY

Acetone-butanol fermentation of sweet potato (SP) cultivar Hi-Dri W-190, supplemented with phosphate and nitrogen sources, was optimized using response surface methodology (RSM). The range of components examined as (g/100 g slurry, SPS): starch, 5.40 to 4.05; CaCO3, 0.3 to 0.1; (NH4)2SO4, 0.6 to 0.2; and KH2PO4, 0.03 to 0.01. SPS was inoculated with 24 h culture of Clostridium acetobutylicum P262 using 2% inoculum containing 1.3 x 10(8) cells ml-1 and incubated anaerobically at 34-degrees-C. Statistical analyses indicated that starch and calcium carbonate significantly affected yields and productivities, but phosphate and nitrogen did not. Response surface regression and consequent canonical analyses established the following optimal concentrations (g/100 g SPS): starch, 4.54; CaCo3, 0.24, (NH4)2SO4, 0.24; KH2PO4, 0.01 for maximal yield, and starch 5.15; CaCO3, 0.29; (NH4)2SO4, 0.14; KH2PO4, 0.009; for maximal productivity. Predicted yield and productivity at stationary points were 34.2% and 0.17 g solvents l-1 h-1, respectively, but experimental yield and productivity were 33.2% and 0.18 g solvents l-1 h-1 when quantitative variables were kept at optimal concentrations.