Ethanol fermentation from sweet sorghum juice
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In recent years bio-ethanol, considered the cleanest liquid fuel alternative to fossil fuels derived from agricultural staples or waste has been of great interest as the ethanol consumption is expected to reach 11.2 billion gallons by 2012. Sweet sorghum containing 18-20% fermentable sugar is an ideal feedstock grown in the Southeast and Midwest states for its easy ethanol fermentation by yeast. The objective is to optimize the fermentation efficiency and ethanol production by varying strategies to process the juice before fermentation, and perform kinetic study to determine the factors that may affect the rate of sugar consumption and ethanol production during fermentation of two different varieties of juice. Even though variety 2 has a higher ethanol yield (35 g/L) than variety 1 (25 g/L), yet variety 1 has a faster consumption and production rate due to its' lower glucose and sucrose proportion in the juice than in variety 2. Applying the Michaelis-Menten model, the consumption rate for variety 1 juice is 5.8 g/L.hr while variety 2 is 3.8 g/L.hr. Microbe concentration may need to be increased for a higher rate for variety 2. Fermentation efficiency is above 90% for frozen and autoclaved juice, and 25% sugar content juice except 30% sugar content juice had the lowest fermentation efficiency of 79%. All these results help us understand the different processing conditions of sweet sorghum juice during fermentation.
