Optimization of Yeast and Enzyme Dose for Dry-Grind Corn Fermentation Process for Ethanol Production

Ethanol production in the dry grind ethanol industry is done by converting the starch in corn to ethanol using enzymes and yeast. This study was conducted to determine the effects of initial enzyme and yeast dose on starch-to-glucose and glucose-to-ethanol conversion, and to optimize the yeast and enzyme dose for the production of ethanol and sugar during the simultaneous saccharification and fermentation (SSF) process. The dry grind fermentation laboratory procedure was used for evaluating the effect of yeast and enzyme dose on the ethanol yield-time profile. Fermentation was performed on a yellow dent corn hybrid with three enzymes doses (80, 110, and 140 microliter) of Spirizyme glucoamylase enzyme and three yeast doses (2, 4, and 6 mL of 0.1 g dry yeast per mL of slurry). Samples were taken at 2, 4, 6, 8, 10, 12, 24, 48, and 72 h from the start of SSF. Samples were analyzed using high-pressure liquid chromatography (HPLC) and near-infrared spectroscopy for the ethanol and sugar contents. Each treatment was replicated three times. Response surface methodology (RSM) was used for studying effects of treatment on the response and optimization of the SSF process. It was found that both enzyme and yeast dose had a significant effect on the level of sugar present during the SSF process. However, only yeast dose had a significant effect on the ethanol content. Effect of treatment on the responses was also found to be dependent on the time after the fermentation. Both HPLC and NIR measurements found that time was the most significant factor affecting ethanol yield, followed by yeast dose and the interaction between time and yeast. For total soluble sugars, time, enzyme dose, yeast dose, and the interaction between yeast and enzyme dose were significant factors. Response surface analysis indicated that for the given range of yeast and enzyme dose, ethanol increases with an increase in yeast dose and a decrease in enzyme dose.