Abstract
High initial glucose concentrations may inhibit glucose utilization and decrease ethanol fermentation efficiency. To minimize substrate inhibition, the effects of feeding yeast with different glucose concentrations on the ethanol production by batch and fed-batch cultures in a 5-L fermentor were investigated. When a batch culture system with Saccharomyces cerevisiae was used for ethanol fermentation with glucose concentrations ranging 10–260 g/L, as a result, 0.2–7.0 g/L biomass and 5.1–115.0 g/L ethanol were obtained. However, substrate inhibition was observed with the initial glucose concentrations greater than 200 g/L in the fermentative media. When a fed-batch culture system (an initial glucose concentration of 180 g/L and total glucose concentration of 260 g/L) was performed, the maximum ethanol concentrations and ethanol yield were significantly higher than those of the batch cultures. The cell biomass, maximum ethanol concentration, and ethanol yields for the fed-batch fermentation cultures were 8.3 g/L, 130.1 g/L and 51% (100% of the theoretical value), respectively. The results indicated that high ethanol concentration and ethanol yield could be achieved by the fed-batch cultures with total glucose concentrations up to 260 g/L.
Highlights
The increasing consumption of crude oil and greenhouse effects connected with petroleum combustion has initiated a worldwide concern for the development of alternative and renewable fuels that are environmentally friendly
Glucose was depleted within 20 h, by which time the ethanol concentration and ethanol yield reached 1.6 glucose and ethanol (g/L) and 50%, respectively
It has been reported that decreases in the growth and viability of yeasts occur as sugar concentrations in the media increase from 12% to 18% (w/v) [9,11,12]; when initial glucose concentrations were higher than 18% (w/v), they had a considerable inhibitory effect on yeast cell growth, ethanol concentration and ethanol yield
Summary
The increasing consumption of crude oil and greenhouse effects connected with petroleum combustion has initiated a worldwide concern for the development of alternative and renewable fuels that are environmentally friendly. Bioethanol is believed to be one such alternative, which can be produced from renewable biomasses such as sugar, starch and cellulosic materials. Bioethanol is a renewable energy source that is well positioned to be an excellent clean-burning, high-energy alternative fuel to gasoline. Bioethanol is commonly blended with conventional gasoline for use in automobile fuels to reduce greenhouse gases emissions. Because the raw materials used to produce bioethanol come from renewable resources with low CO2 emissions, bioethanol has offered many distinctive advantages over fossil fuels [1]. Saccharomyces cerevisiae is the well-known brewing yeast that can ferment glucose into ethanol under anaerobic conditions. The microorganism is ideal for ethanol production because it possesses
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