The Kinetics of Ethanol Fermentation Based on Adsorption Processes

Liu, Zhen

doi:10.15255/kui.2013.023

Cited by 2 publications

(1 citation statement)

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“…In biological membranes, water penetrates the lipid bilayer and forms hydrogen bonds with the polar groups of phospholipids, at increased ethanol concentrations, this water is replace by ethanol, altering the structure and function of the membrane [50]. Another possibility is that ethanol denatures proteins by interacting with non-polar parts of the molecules [51].…”

Section: Yeast Viabilitymentioning

confidence: 99%

Effects of Ultrasound on Fermentation of Glucose to Ethanol by Saccharomyces cerevisiae

2019

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Previous studies have shown that pretreatment of corn slurries using ultrasound improves starch release and ethanol yield during biofuel production. However, studies on its effects on the mass transfer of substrates and products during fermentation have shown that it can have both beneficial and inhibitory effects. In this study, the effects of ultrasound on mass transfer limitations during fermentation were examined. Calculation of the external and intraparticle observable moduli under a range of conditions indicate that no external or intraparticle mass transfer limitations should exist for the mass transfer of glucose, ethanol, or carbon dioxide. Fermentations of glucose to ethanol using Saccharomyces cerevisiae were conducted at different ultrasound intensities to examine its effects on glucose uptake, ethanol production, and yeast population and viability. Four treatments were compared: direct ultrasound at intensities of 23 and 32 W/L, indirect ultrasound (1.4 W/L), and no-ultrasound. Direct and indirect ultrasound had negative effects on yeast performance and viability, and reduced the rates of glucose uptake and ethanol production. These results indicate that ultrasound during fermentation, at the levels applied, is inhibitory and not expected to improve mass transfer limitations.Ultrasound generates alternating high-and low-pressures, causing compression and rarefaction cycles in the medium. Rarefaction leads to the formation of cavities, which implode during compression [8,9]. This is a function of the frequency and the amplitude of the oscillations. The sudden drop in pressure creates vacuum bubbles or cavities. This is followed by a rapid return to the original pressure, which causes the cavities to collapse, releasing energy, which is then transferred to the medium [9]. The intensity of cavitation creates high local temperatures and powerful pressures for brief periods of time [8]. This could potentially have beneficial effects on mass transfer.Ultrasound has been used in bioprocessing for different purposes and with different types of equipment and methods of application. It has been used in feedstock pretreatment for de-agglomeration, particle size reduction, dispersion [6,10-15], particle separation [16], and corn ethanol and wastewater treatment processes [17,18]. It has also been used to disrupt cells [19][20][21][22][23][24] and cell membranes, allowing the recovery of intracellular components [25,26] and for the inactivation of microbes [27,28].A few studies have focused on the benefits of ultrasound during fermentation. Improvements were found due to enhanced mixing, cell deagglomeration, and facilitating the release of CO 2 from the medium, lowering its concentration [23,[29][30][31][32][33][34]. Another mechanism by which ultrasound may impact ethanol fermentation is by reducing mass transfer limitations for glucose, ethanol, and carbon dioxide in the vicinity of yeast cells [35,36]. Mass transfer limitations may limit the rate of fermentation by reducing glucose concentration at the cell s...

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Section: Yeast Viabilitymentioning

confidence: 99%