High Gravity Conditions Research Articles

The use of dried spent yeast as a low-cost nitrogen supplement in ethanol fermentation from sweet sorghum juice under very high gravity conditions

Dried spent yeast (DSY) was used as a low-cost nitrogen supplement for ethanol fermentation from sweet sorghum juice under very high gravity (VHG) conditions by Saccharomyces cerevisiae NP 01. The fermentation was carried out at 30oC in a 5-litre bioreactor. The results showed that DSY promoted ethanol production efficiencies. The ethanol concentration ( P ), productivity ( Q p ) and yield ( Y p/s ) of the sterile juice (total sugar of 280 g l -1 ) supplemented with 8 g l -1 of DSY were not different from those supplemented with yeast extract and/or peptone at the same amount. The initial yeast cell concentration of 5 x 10 7 cells ml -1 was found to be optimal for scale-up ethanol production. In addition, an increase in sugar concentration in inoculum preparation medium (from 10 to 100 g l -1 ) improved the ability of the inoculum to produce ethanol under the VHG conditions. When S. cerevisiae NP 01 grown in the juice containing 100 g l -1 of total sugar was used as the inoculum for ethanol fermentation, the P , Q p and Y p/s obtained were 108.98 ± 1.16 g l -1 , 2.27 ± 0.06 g l -1 h -1 and 0.47 ± 0.01 g g -1 , respectively. Similar results were also observed when the ethanol fermentation was scaled up to a 50-litre bioreactor under the same conditions. The cost of the sweet sorghum for ethanol production was US$ 0.63 per litre of ethanol. These results clearly indicate the high potential of using sweet sorghum juice supplemented with DSY under VHG fermentation for ethanol production in industrial applications.

Consolidated bioprocessing strategy for ethanol production from Jerusalem artichoke tubers by Kluyveromyces marxianus under high gravity conditions

Developing an innovative process for ethanol fermentation from Jerusalem artichoke tubers under very high gravity (VHG) conditions. A consolidated bioprocessing (CBP) strategy that integrated inulinase production, saccharification of inulin contained in Jerusalem artichoke tubers and ethanol production from sugars released from inulin by the enzyme was developed with the inulinase-producing yeast Kluyveromyces marxianus Y179 and fed-batch operation. The impact of inoculum age, aeration, the supplementation of pectinase and nutrients on the ethanol fermentation performance of the CBP system was studied. Although inulinase activities increased with the extension of the seed incubation time, its contribution to ethanol production was negligible because vigorously growing yeast cells harvested earlier carried out ethanol fermentation more efficiently. Thus, the overnight incubation that has been practised in ethanol production from starch-based feedstocks is recommended. Aeration facilitated the fermentation process, but compromised ethanol yield because of the negative Crabtree effect of the species, and increases the risk of contamination under industrial conditions. Therefore, nonaeration conditions are preferred for the CBP system. Pectinase supplementation reduced viscosity of the fermentation broth and improved ethanol production performance, particularly under high gravity conditions, but the enzyme cost should be carefully balanced. Medium optimization was performed, and ethanol concentration as high as 94·2 g l(-1) was achieved when 0·15 g l(-1) K(2) HPO(4) was supplemented, which presents a significant progress in ethanol production from Jerusalem artichoke tubers. A CBP system using K. marxianus is suitable for efficient ethanol production from Jerusalem artichoke tubers under VHG conditions. Jerusalem artichoke tubers are an alternative to grain-based feedstocks for ethanol production. The high ethanol concentration achieved using K. marxianus with the CBP system not only saves energy consumption for ethanol distillation, but also significantly reduces the amount of waste distillage discharged from the distillation system.

Bioethanol production from sugar beet molasses and thick juice using Saccharomyces cerevisiae immobilized on maize stem ground tissue

The potential of by-products and intermediate products of sugar beet processing as raw materials for bioethanol production in Vojvodina region has a big scope in view of the demand of ethanol as an alternative for fossil fuels. Also, from ecological point of view, use of agricultural waste as carriers for cells immobilization is justifiable. The biocatalyst prepared by immobilization of Saccharomyces cerevisiae on maize stem ground tissue was used for batch fermentation of sugar beet molasses and thick juice under normal and very high gravity (VHG) conditions. Cell immobilization was observed by electron microscopy. The carrier was effective for cell immobilization and provided strength and stability to the yeast cell mass and functioned as a fortification against toxins and inhibitors, enabling efficient ethanol fermentation, particularly in VHG conditions. Three different initial glucose concentrations were tested: 100, 150 and 300g/l. The maximum ethanol concentration of 83.20g/l for molasses and 132.39g/l for thick juice were achieved in VHG fermentation by immobilized cells, whereas the free yeast cells were unsuccessful in the same media. Taking into consideration significant process parameters sugar beet thick juice was found to be economically favorable, compared to molasses, particularly in the VHG fermentation process.

Optimization of bioethanol production during simultaneous saccharification and fermentation in very high-gravity cassava mash

Hydrolysis and fermentation conditions for production of ethanol from very high-gravity cassava mash by Saccharomyces cerevisiae during simultaneous saccharification and fermentation (SSF) processing were optimized using a statistical methodology. During the first part of the study, Placket-Burman design (PBD) was used to study 19 factors that could potentially influence ethanol production. Gravity, particle size, initial pH, and fermentation temperature were identified as key factors that significantly increased final ethanol concentration. The main and interaction effects of these factors were subsequently evaluated based on a quadratic equation generated by central composite design (CCD) using response-surface methodology (RSM). Under the optimized very high-gravity conditions, the final ethanol concentration obtained from experiment increased from 8.21% (wt.%) to 15.03% (wt.%) and was in good agreement with model prediction. By employing two other commercial Saccharomyces strains, similar results were obtained under the same optimized condition. Therefore, we conclude that final ethanol concentration, ethanol productivity (V (P/max)), glucose utilization (Y (G/s), Y (P/s)), and fermentation efficiency (η (f)) were enhanced or maintained under the optimized condition of 40% gravity, 390μm particle size, initial pH 5.5, and 27°C fermentation temperature.

Heater Size and Gravity Based Pool Boiling Regime Map: Transition Criteria Between Buoyancy and Surface Tension Dominated Boiling

A pool boiling regime map demarcating the boundary between the surface tension and buoyancy dominated boiling regimes is developed based on heater size and gravity. For large heaters and/or high gravity conditions, boiling is dominated by buoyancy, and the ebullition cycle dominates the contribution to heat transfer. As the gravity level and/or heater size is decreased, surface tension forces become increasingly dominant, and a decrease in heat transfer is observed. The ratio of the heater size Lh (length of a side for a square heater) to the capillary length Lc is found to be a suitable parameter to define the transition criterion between these regimes. Based on the data obtained using FC-72 and pentane, the threshold value of Lh/Lc above which pool boiling is buoyancy dominated was found to be about 2.1. This transition criterion was found to be the same for gravity levels between ∼0g–1.7g and liquid subcoolings between 6.6°C and 26.6°C.

Global transcription engineering of brewer’s yeast enhances the fermentation performance under high-gravity conditions

Global transcription engineering was developed as a tool to reprogram gene transcription for eliciting new phenotypes important for technological applications (Science 2006, 314(5805):1565-1568). A recent report indicated that the beneficial growth advantage of yeast cells expressing the SPT15-300 mutation is the result of enhanced uptake and/or improved utilization of leucine and thus was seen only on defined media with low concentrations of leucine (Appl Environ Microbiol 2009, 75(19):6055-6061). Further investigation towards a leucine-prototrophic strain of industrial lager brewer's yeast indicated that integration one copy of SPT15-300 in SPT15 allele, however, did lead to an increased ethanol tolerance on complex rich medium at high gravity fermentation condition. Under brewing conditions, the SPT15-300 mutant produced 80.78 g/L ethanol from 200 g/L carbohydrates after 384 h, almost twice as much as that of the wild-type strain. The results convinced us that the effect of global regulator modification of yeast is at multi-genes level and is extremely complicated.

Reduction Kinetics of Iron Oxides in Molten Lunar Soil Simulant by Graphite

In space exploration including the utilization of materials and energy outside the earth, construction of a moon base is one of considerable measures to develop the front line. Due to the huge cost of transportation from the earth, structural materials such as iron should be in-situ produced on the moon. Fortunately, the Apollo 14 mission has reported that the lunar soil contains about 10 mass% of iron oxides. When considering ironmaking from lunar soils by graphite on the moon, understanding the reduction behaviour should come first but has not yet been attempted for iron resources whose concentration of iron oxides is as low as 10 mass%. Thus, the present work has focused on reduction kinetics of iron oxides in molten lunar soil simulant by graphite, and apparent rate constants for reduction reactions have been derived from experiments with systematic variation in reduction conditions for comprehensive discussion about the reaction mechanism. The apparent rate constant derived is 2.0×10−4 cm/s at 1803 K and the corresponding activation energy estimated is about 360 kJ/mol. The use of a graphite rod rotation mechanism enabled the stirring condition to be changed, resulting in a finding that stronger stirring shifts the rate-determining step from reduction of FeO by CO gas to direct reduction of FeO by graphite. On the basis of all these kinetic findings, it is likely that ironmaking from lunar soils by graphite on the moon is possible in that high vacuum and low gravity conditions would probably promote the removal of CO gas film from the graphite surface.

High-Gravity Brewing and Distilling—Past Experiences and Future Prospects

High-gravity brewing employs wort (15–20°P original gravity) at a higher than normal concentration, and to obtain sales-gravity beer, dilution with water (usually carbon filtered and deoxygenated) is required at a later stage in processing. Using this method, increased production demands can be met without significant expansion of brewing, fermenting, and storage facilities. Scotch whisky production, particularly grain whisky, also is increasingly employing high-gravity techniques (18–21°P wort) during a continuous fermentation procedure. The principal advantage to this procedure is the more efficient use of existing processes. The disadvantages of high-gravity brewing include decreased beer foam stability, a variety of stress effects on yeast, and problems with beer flavor matching compared with sales-gravity brewed beers. The stress effects of high-gravity wort also include enlargement of the yeast vacuole and changes in the topography of the yeast cell surface. Hydrodynamic stress effects on yeast are also a problem, particularly when employing centrifugation at the end of fermentation to crop yeast for recycling into a subsequent fermentation. Finally, difficulties encountered in both brewing and distilling include the inability of yeast to completely utilize the largest fermentable wort sugar—maltotriose. This is particularly the case during grain whisky production by continuous fermentation under high-gravity wort conditions.

Histone modifying proteins Gcn5 and Hda1 affect flocculation in Saccharomyces cerevisiae during high-gravity fermentation

The performance of yeast is often limited by the constantly changing environmental conditions present during high-gravity fermentation. Poor yeast performance contributes to incomplete and slow utilization of the main fermentable sugars which can lead to flavour problems in beer production. The expression of the FLO and MAL genes, which are important for the performance of yeast during industrial fermentations, is affected by complex proteins associated with Set1 (COMPASS) resulting in the induction of flocculation and improved maltose fermentation capacity during the early stages of high-gravity fermentation. In this study, we investigated a possible role for other histone modifying proteins. To this end, we tested a number of histone deacetylases (HDACs) and histone acetyltransferases and we report that flocculation is induced in absence of the histone deacetylase Hda1 or the histone acetyltransferase Gcn5 during high-gravity fermentation. The absence of Gcn5 protein also improved utilization of high concentrations of maltose. Deletion of SIR2 encoding the HDA of the silent informator regulator complex, did not affect flocculation under high-gravity fermentation conditions. Despite the obvious roles for Hda1 and Gcn5 in flocculation, this work indicates that COMPASS mediated silencing is the most important amongst the histone modifying components to control the expression of the FLO genes during high-gravity fermentation.

Synthesis of single-walled carbon nanotubes by arc-vaporization under high gravity condition

Arc-vaporization is one of the common methods to synthesize single-walled carbon nanotubes (SWNTs). However the detailed synthesis mechanism is still not clear, and the synthesis of longer and chirality-selected SWNTs has not been obtained. Here influence of the gravity G = 1 g 0, 2 g 0, and 3 g 0 is studied in order to develop the synthesis method of SWNTs. Simultaneously, calculations of heat convection are also carried out by using a fluid simulation program and the results are compared with the experimental results.

On-line estimation of biomass, glucose and ethanol in Saccharomyces cerevisiae cultivations using in-situ multi-wavelength fluorescence and software sensors

Batch bioreactor cultivations using Saccharomyces cerevisiae at high (190–305 g l −1 glucose) or low (21–25 g l −1 glucose) gravity conditions were monitored on-line using multi-wavelength fluorescence (MWF) and standard monitoring sensors. Partial least squares models were calibrated for the prediction of cell dry weight (CDW), ethanol and consumed glucose, using the two data types separately. The low gravity cultivations (LGCs) consisted of two phases (glucose consumption with concomitant ethanol production followed by ethanol consumption after glucose depletion), which proved difficult to model using one and the same model for both phases. Segmented modelling, using different models for the two phases, improved the predictions significantly. The prediction models calibrated on standard on-line process data displayed similar or lower root mean square error of prediction (RMSEP) compared to the fluorescence models. The best prediction models for high gravity cultivations (HGCs) had RMSEPs of 1.0 g l −1 CDW, 1.8 g l −1 ethanol and 5.0 g l −1 consumed glucose, corresponding to 4%, 2% and 2% of the respective concentration intervals. Corresponding numbers in low gravity models were 0.3 g l −1 CDW, 0.7 g l −1 ethanol and 1.0 g l −1 consumed glucose, corresponding to 4%, 8% and 4% of the respective concentration intervals.

Effects of dynamic load on flow and heat transfer of two-phase boiling water in a horizontal pipe

An experimental investigation was performed to obtain the flow and heat transfer characteristics of single-phase water flow and two-phase pipe boiling water flow under high gravity (Hi-G) in present work. The experiments were conducted on a rotating platform, and boiling two-phase flow state was obtained by means of electric heating. The data were collected specifically in the test section, which was a lucite pipe with inner diameter of 20 mm and length of 400 mm. By changing the parameters, such as rotation speed, inlet temperature, flow rate, and etc., and analyzing the fluid resistance, effective heat and heat transfer coefficient of the experimental data, the effects of dynamic load on the flow and heat transfer characteristics of single phase water and two-phase boiling water flow were investigated and obtained. The two-phase flow patterns under Hi-G condition were obtained with a video camera. The results show that the dynamic load significantly influences the flow characteristic and boiling heat transfer of the two-phase pipe flow. As the direction of the dynamic load and the flow direction are opposite, the greater the dynamic load, the higher the outlet pressure and the flow resistance, and the lower the flow rate, the void fraction, the wall inner surface temperature and the heat transfer capability. Therefore, the dynamic load will block the fluid flow, enhance heat dissipation toward the ambient environment and reduce the heat transfer to the two-phase boiling flow.

Metabolic flux and cell cycle analysis indicating new mechanism underlying process oscillation in continuous ethanol fermentation with Saccharomyces cerevisiae under VHG conditions

Process oscillation characterized by long oscillation period and large oscillation amplitude was observed in continuous ethanol fermentation with Saccharomyces cerevisiae under very high gravity conditions. Metabolic flux analysis was applied to the fermentation system, and the results indicated that carbon flux distributions at the metabolic notes oscillated, correspondingly, and the root reason for the process oscillation was the intracellular metabolism of yeast cells. Cell cycle analysis with the flow cytometry showed that no cell-cycle-dependent synchronization of the daughter and mother cells occurred within the duration of the oscillation, and thus different mechanism existed compared with the oscillation observed in the continuous culture of Saccharomyces cerevisiae and triggered by the synchronization of the daughter and mother cells under specific conditions. Furthermore, the overall metabolic activity of the yeast cells was examined, which was found not exactly out of phase but lag behind ethanol concentration that accumulated within the fermentation system and its inhibition on the yeast cells as well, which supported the mechanistic speculation for the process oscillation: the lag response of yeast cells to ethanol inhibition.

Phase-separation of lead borate glasses under different gravity conditions

Glasses with the composition 3.5PbO·96.5B2O3 were melted and solidified through drop shaft experiment and ground experiment to explore the phase-separation of the glass under abnormal gravity condition. The composition homogeneity and the microstructure for different samples were compared. Results show that all the samples phase-separated into two different glass phases, the separated Pb-rich phase and the continuous B-rich phase, regardless of the gravity level in which the phase-separation happened. For the sample from experiment PB-1, the size of separated Pb-rich phase in the top is much smaller than that in the bottom. The big heterogeneity in composition along the vertical direction and obvious differences in microstructures for this sample could be attributed to the high gravity condition that the phase-separation occurred. There is no visible composition heterogeneity and the microstructure difference for the samples from experiments PB-2 and PB-G.

Effect of Gravity on the Gelation of Silica Sols

Acid-catalyzed silica polymerization was carried out under gravity conditions varied from 0.01g aboard a reduced gravity aircraft to 70g in a centrifuge. The silicate connectivity of the final xerogels was analyzed using solid state 29Si NMR and the porosity using nitrogen adsorption. Gravity was found to have an important influence on the occurrence of intra- and intermolecular condensation reactions. Under reduced gravity buoyancy driven-free convection is limited and silica polymerization occurs in a diffusion-limited regime. Intramolecular condensations and densifications prevail and extended coils of cages are formed through cyclization reactions in the sol particles. In terrestrial and high-gravity conditions, bimolecular reactions compete more favorably with internal condensations. More open structures composed of chains and rings are formed. These flexible species delay the onset of gelation, leading to an increase in gelation time as the gravity level is increased. During the subsequent drying procedure, pore collapse changes the structure from meso- to microporous. The porosity of the finally obtained xerogels is mostly defined by the drying conditions of the gel, irrespective of the silicate connectivity.

E225 地球、火星、月でのPMMA上の火炎の燃え拡がり現象の数値計算(固体燃焼・微小重力燃焼・触媒燃焼)

It is planned to launch Orion Crew Vehicle to International Space Station, Moon and Mars by NASA. The fire protection is the most important problem in the cabin of low pressure, high Oxygen mass fraction and low gravity conditions. The experimental test of flame spread over flammable material in low gravity requires huge cost and it is actually unacceptable. This study tested upward flame spread over PMMA in different conditions of pressure, Oxygen mass fraction and gravity by numerical simulations. The flame spread speed and peak heat release fell as gravity was dropped at same pressure and Oxygen mass fraction conditions.

Isolation and Characterization of Brewer's Yeast Variants with Improved Fermentation Performance under High-Gravity Conditions

To save energy, space, and time, today's breweries make use of high-gravity brewing in which concentrated medium (wort) is fermented, resulting in a product with higher ethanol content. After fermentation, the product is diluted to obtain beer with the desired alcohol content. While economically desirable, the use of wort with an even higher sugar concentration is limited by the inability of brewer's yeast (Saccharomyces pastorianus) to efficiently ferment such concentrated medium. Here, we describe a successful strategy to obtain yeast variants with significantly improved fermentation capacity under high-gravity conditions. We isolated better-performing variants of the industrial lager strain CMBS33 by subjecting a pool of UV-induced variants to consecutive rounds of fermentation in very-high-gravity wort (>22 degrees Plato). Two variants (GT336 and GT344) showing faster fermentation rates and/or more-complete attenuation as well as improved viability under high ethanol conditions were identified. The variants displayed the same advantages in a pilot-scale stirred fermenter under high-gravity conditions at 11 degrees C. Microarray analysis identified several genes whose altered expression may be responsible for the superior performance of the variants. The role of some of these candidate genes was confirmed by genetic transformation. Our study shows that proper selection conditions allow the isolation of variants of commercial brewer's yeast with superior fermentation characteristics. Moreover, it is the first study to identify genes that affect fermentation performance under high-gravity conditions. The results are of interest to the beer and bioethanol industries, where the use of more-concentrated medium is economically advantageous.

Proteomic Analysis of Saccharomyces cerevisiae under High Gravity Fermentation Conditions

Saccharomyces cerevisiae KAY446 was utilized for ethanol production, with glucose concentrations ranging from 120 g/L (normal) to 300 g/L (high). Although grown in a high glucose environment, S. cerevisiae still retained the ability to produce ethanol with a high degree of glucose utilization. iTRAQ-mediated shotgun proteomics was applied to identify relative expression change of proteins under the different glucose conditions. A total of 413 proteins were identified from three replicate, independent LC-MS/MS runs. Unsurprisingly, many proteins in the glycolysis/gluconeogenesis pathway showed significant changes in expression level. Twenty five proteins involved in amino acid metabolism decreased their expression, while the expressions of 12 heat-shock related proteins were also identified. Under high glucose conditions, ethanol was produced as a major product. However, the assimilation of glucose as well as a number of byproducts was also enhanced. Therefore, to optimize the ethanol production under very high gravity conditions, a number of pathways will need to be deactivated, while still maintaining the correct cellular redox or osmotic state. Proteomics is demonstrated here as a tool to aid in this forward metabolic engineering.

Aluminum oxide thin dielectric film formation under elevated gravity conditions

In an attempt to grow low defect, dense crystalline aluminum hydrous oxide [AlO(OH)] films with better dielectric properties, hydration experiments on a high purity, high cubicity aluminum foil were conducted in deionized water at 85 °C under high gravity conditions. Fields from 100 up to 14,100 g and reaction times from 1 min up to 6 h were used. The films obtained were examined by field emission-scanning electron microscopy and X-ray diffraction. Hydration for up to 30 min using g-forces up to 3000 g showed the presence of only one crystalline phase with particle size 20–30 nm identified as pseudo-boehmite. A second phase, bayerite, was found to be growing from the pseudo-boehmite film at times greater than 30 min using fields above 5000 g.

P- and n-Type Charge Transport in Field-Effect Transistors of Pristine Poly(p-Phenylenevinylene)

ABSTRACTPoly(p-phenylenevinylene) (PPV) thin films were prepared by using drop casting under high gravity condition and p- and n-type PPV based field effect transistors (FET) have been fabricated. PPV FETs with gold source-drain electrodes showed the p-channel FET conduction. The FET characteristics of PPV were improved by annealing and the field-effect hole mobility was 8.8×10−4cm2V−1s−1. On the other hand, PPV FET with calcium source-drain electrodes showed the n-channel FET conduction and the field-effect electron mobility was 1.0×10−6cm2V−1s−1.