Process optimization for ethanol production from very high gravity (VHG) finger millet medium using response surface methodology

The Box-Wilson central composite design (CCD) based on response surface methodology (RSM) was used for ethanol fermentation using very high gravity (VHG) finger millet hydrolysate. Optimized process variables were namely, concentrations of yeast extract, magnesium sulphate and pH of the medium. High gravity mashes (>300 g dissolved solids per liter) were prepared by a thermo-stable α-amylase, followed by simultaneous saccharification and fermentation (SSF) at 30ºC for 60 h. Ethanol concentration as high as 13.66% (v/v) was obtained after optimizing the variables. The coefficient of determination (R2) value of 0.9808 indicates the goodness of fit for regression model. The predicted values for optimization process conditions were in good agreement with experimental data. The optimum values for tested variables were yeast extract 7.13 (g/l) magnesium sulphate 23.32 mM and pH 4.8. Verification of the model indicated no significant difference between predicted and observed values.