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1.
John D. Wright Charles E. Wyman Karel Grohmann 《Applied biochemistry and biotechnology》1988,18(1):75-90
Simultaneous saccharification and fermentation (SSF) processes for producing ethanol from lignocellulose are capable of improved
hydrolysis rates, yields, and product concentrations compared to separate hydrolysis and fermentation (SHF) systems, because
the continuous removal of the sugars by the yeasts reduces the end-product inhibition of the enzyme complex. Recent experiments
using Genencor 150L cellulase and mixed yeast cultures have produced yields and concentrations of ethanol from cellulose of
80% and 4.5%, respectively. The mixed culture was employed because B.clausenii has the ability to ferment cellobiose (further reducing end-product inhibition), while the brewing yeastS. cerevisiae provides a robust ability to ferment the monomeric sugars. These experimental results are combined with a process model to
evaluate the economics of the process and to investigate the effect of alternative processes, conditions, and organisms. 相似文献
2.
Experimental results are presented for continuous conversion of pretreated hardwood flour to ethanol. A simultaneous saccharification
and fermentation (SSF) system comprised ofTrichoderma reesei cellulase supplemented with additional β-glucosidase and fermentation bySaccharomyces cerevisiae was used for most experiments, with data also presented for a direct microbial conversion (DMC) system comprised ofClostridium thermocellum. Using a batch SSF system, dilute acid pretreatment of mixed hardwood at short residence time(10 s, 220°C, 1% H2SO4) was compared to poplar wood pretreated at longer residence time (20 min, 160°C, 0.45% H2SO4). The short residence time pretreatment resulted in a somewhat (10–20%) more reactive substrate, with the reactivity difference
particularly notable at low enzyme loadings and/or low agitation. Based on a preliminary screening, inhibition of SSF by byproducts
of short residence time pretreatment was measurable, but minor. Both SSF and DMC were carried out successfully in well-mixed
continuous systems, with steady-state data obtained at residence times of 0.58–3 d for SSF as well as 0.5 and 0.75 d for DMC.
The SSF system achieved substrate conversions varying from 31% at a 0.58-d residence time to 86% at a 2-d residence time.
At comparable substrate concentrations (4–5 g/l) and residence times (0.5–0.58 d), substrate conversion in the DMC system
(77%) was significantly higher than that in the SSF system (31%). Our results suggest that the substrate conversion in SSF
carried out in CSTR is relatively insensitive to enzyme loading in the range 7–25 U/g cellulose and to substrate concentration
in the range of 5–60 g/L cellulose in the feed. 相似文献
3.
Rosa S. M. A. Felipe M. G. A. Silva S. S. Vitolo M. 《Applied biochemistry and biotechnology》1998,(1):127-135
The effect of pH, time of fermentation, and xylose and glucose concentration on xylitol production, cell growth, xylose reductase
(XR), and xylitol dehydrogenase (XD) activities ofCandida guilliermondii FTI 20037 were determined. For attaining XR and XD activities of 129-2190 U/mg of protein and 24-917 U/mg of protein, respectively,
the cited parameters could vary as follows: initial pH: 3.0-5.0; xylose: 15-60 g/L; glucose: 0-5 g/L; and fermentation time:
12-24 h. Moreover, the high XR and XD activities occurred when the xylitol production by the yeast was less than 19.0 g/L. 相似文献
4.
Ballesteros I. Oliva J. M. Carrasco J. Cabañas A. Navarro A. A. Ballesteros M. 《Applied biochemistry and biotechnology》1998,(1):369-381
In this work, the effect of the addition of different concentrations of Tween-80 and three different zeolite-like products
on enzymatic hydrolysis, ethanol fermentation, and simultaneous saccharification and fermentation (SSF) process has been investigated.
The ability of these products to enhance the effectiveness of the SSF process to ethanol of steam-exploded poplar biomass
using the thermotolerant strainKluyveromyces marxianus EMS-26 has been tested.
Tween-80 (0.4 g/L) increased enzymatic hydrolysis yield by 20% when compared to results obtained in hydrolysis in absence
of the additive. Zeolite-like products (ZESEP-56 and ZECER-56) (2.5 g/L) improved rates of conversion and ethanol yields in
the fermentation of liquid fraction recovered from steam-exploded poplar. The periods required for the completion of fermentation
were approx 10 h in the presence of zeolite-like products and 24 h in the absence of additives. The probable mode of action
is through lowered levels of inhibitory substances because of adsorption by the additive. 相似文献
5.
In this technoeconomic evaluation of the manufacture of acetic acid by fermentation, the use of the bacterium:Acetobacter suboxydans from the old vinegar process was compared with expected performance of the newerClostridium thermoaceticum bacterium. Both systems were projected to operate as immobilized cells in a continuous, fluidized bed bioreactor, using solvent
extraction to recover the product.
Acetobacter metabolizes ethanol aerobically to produce acid at 100 g/L in a low pH medium. This ensures that the product is in the form
of a concentrated extractable free acid, rather than as an unextractable salt. Unfortunately, yields from glucose by way of
the ethanol fermentation are poor, but near the biological limits of the organisms involved. 相似文献
6.
The effect of the trace metals Cu, K, Na, and Ca, separately or in mixture, on fermentation time, ethanol production rate,
and cell growth in the fermentation of synthetic media containing sucrose is discussed. The results are related to the range
of contents found in raw materials, molasses and raisins, in order to determine their optimum concentrations for alcohol production. 相似文献
7.
In this paper a heterogeneous model is developed for the alcoholic fermentation process. The model is expressed in terms of
intracellular and extracellular concentrations of ethanol and sugar as well as biomass concentration as state variables. The
model takes into consideration the floc size and the mass transfer rates of both ethanol and sugar. The intrinsic kinetics
of the process used in the model was developed from published data which includes the inhibitory effects of ethanol and cells.
The model development is achieved through comparison with one set of experimental results given by Novak et al. (1). The model is then checked against two other sets of experimental results. The developed model is also used to simulate
an industrial fed-batch fermentar. 相似文献
8.
9.
Kaster Jeffrey A. Michelsen Donald L. Velander William H. 《Applied biochemistry and biotechnology》1990,(1):469-484
A microbubble dispersion (MBD) was used to supply oxygen for aerobic fermentations in a standard 2 L stirred tank fermenter.
The microbubble dispersion was formed using only surfactants produced naturally. Growth rates ofSaccharomyces cerevisiae cultures were found to be equal or greater with MBD sparging than with gas sparging. The oxygen transfer coefficent with
MBD sparging was found to be 190/h and independent of impeller speed from 100–580 rpm. The oxygen transfer coefficient with
air sparging rose from 55 to 132/h over the same range of impeller speeds. Power requirements for the fermenter systems were
estimated. 相似文献
10.
Cortez Ely V. Pessoa Adalberto Assis Adilson N. 《Applied biochemistry and biotechnology》1998,(1):661-666
Xylans are the major components of the hemicellulosic fraction of lignocellulosic biomass and their hydrolysis can be obtained
using xylanases fromPenicillium janthinellum. In this work, sugarcane bagasse hemicellulosic hydrolysate was used as the substrate for producing xylanase. The precipitation
of these enzymes was studied using ethanol and Na2SO4 as precipitating agents. Ethanol precipitation experiments were performed batchwise in concentrations ranging from 10 to
80%, pH 4.0 to 7.0, at 4áC. The concentrations used in the precipitations with Na2SO4 were from 5 to 60% at pH 5.5 and 25áC. Solubility curves as a function of xylanase activity and total protein for both precipitating
agents were made. According to the results, Na2SO4 is not appropriate for precipitating xylanases in this medium since at salt concentrations higher than 25%, the enzyme was
denaturated and at this concentration less than 80% of the enzyme and total protein were precipitated. Because of differences
in xylanase and total protein solubility, a fractionated precipitation using ethanol can be performed, since with 40% ethanol,
49% of the total protein was precipitated and more than 95% of the enzyme was kept in solution. On the other hand approx 100%
of the xylanases were recovered by precipitation after adding 80% ethanol. 相似文献
11.
Tucker M. P. Farmer J. D. Keller F. A. Schell D. J. Nguyan Q. A. 《Applied biochemistry and biotechnology》1998,(1):25-35
Single-stage cocurrent dilute acid pretreatments were carried out on yellow poplar (Liriodendron tulipifera) sawdust using an as-installed and short residence time modified pilot-scale Sunds hydrolyzer and a 4-L bench-scale NREL
digester (steam explosion reactor). Pretreatment conditions for the Sunds hydrolyzer, installed in the NREL process development
unit (PDU), which operates at 1 t/d (bone-dry t) feed rate, spanned the temperature range of 160 – 210°C, 0.1 – 1.0% (w/w)
sulfuric acid, and 4-10-min residence times. The batch pretreatments of yellow poplar sawdust in the bench-scale digester
were carried out at 210 and 230°C, 0.26% (w/w) sulfuric acid, and 1-, 3-, and 4-min residence times. The dilute acid prehydrolysis
solubilized more than 90% of the hemicellulose, and increased the enzymatic digestibility of the cellulose that remained in
the solids. Compositional analysis of the pretreated solids and liquors and mass balance data show that the two pretreatment
devices had similar pretreatment performance. 相似文献
12.
Ballesteros I. Oliva J. M. Ballesteros M. Carrasco J. 《Applied biochemistry and biotechnology》1993,(1):201-211
Different treatments to improve the thermotolerance of fermenting yeasts for simultaneous ethanol saccharification and fermentation
process of cellulosic materials have been examined. Yeasts of the generaSaccharomyces andKluyveromyces were tested for growth and fermentation at progressively higher temperatures in the range of 42–47°C. The best results were
obtained withK. marxianus LG, which was then submitted to different treatments in order to achieve thermotolerant clones. A total of 35 new clones
were obtained that dramatically improved the SSF of 10% Solka-floc substrate at 45°C when compared to the original strain,
some with ethanol concentrations as high as 33 g/L. 相似文献
13.
Suva Silvio S. Felipe Maria G. A. Mancilha Ismael M. 《Applied biochemistry and biotechnology》1998,(1):331-339
Xylitol is a sweetener with important technological properties like anticariogenicity, low caloric value, and negative dissolution
heat. Because it can be used successfully in food formulations and pharmaceutical industries, its production is in great demand.
Xylitol can be obtained by microbiological process, since many yeasts and filamentous fungi synthesize the xylose reductase
enzyme, which catalyses the xylose reduction into xylitol as the first step in the xylose metabolism. The xylitol production
by biotechnological means has several economic advantages in comparison with the conventional process based on the chemical
reduction of xylose. The efficiency and the productivity of this fermentation chiefly depends upon the microorganism and the
process conditions employed. In this mini-review, the most significant upstream parameters on xylitol production by biotechnological
process are described. 相似文献
14.
Keller Fcred A. Bates Delicia Ruiz Ray Nguyen Quang 《Applied biochemistry and biotechnology》1998,(1):137-148
Several strains and genera of yeast, includingSaccharomyces cerevisiae D5A,Pachysolen tannophilus, S. cerevisiae K-l,Brettanomyces custersii, Candida shehatae, andCandida acidothermophilum, are screened for growth on dilute acid-pretreated softwood prehydrolysate. Selected softwood species found in forest underbrush
of the western United States, which contain predominantly hexosan hemicellulose, were studied. This phase of the work emphasized
debarked Douglas fir. The two best initial isolates were gradually selected for improved growth by adaptation to increasing
prehydrolysate concentrations in batch culture, with due consideration of nutrient requirements. Microaerophilic conditions
were evaluated to encourage tolerance of pretreatment hydrolysate, as well as ethanol product. Adaptation and simultaneous
saccharification and fermentation (SSF) results are used to illustrate improved performance with an adapted strain, compared
to the wild type. 相似文献
15.
Neurospora crassa XI was found to ferment xylose and glucose simultaneously. Xylose was the appropriate inducer for the production of xylose
reductase that had two isoenzymes designated as EI and EII. Both EI and EII, which were purified by affinity chromatography,
had NADPH-dependent xylose reductase activities. EII also had NADH-dependent activity, and EI is the only xylose reductase
found so far without any NADH-dependent activity. EI and EII had MWs of 30 kDa and 27 kDa, and pIs of 5.6 and 5.2, respectively. The specifities of EI and EII against triose, pentoses, and hexoses were studied. The Kms against xylose for EI and EII were 2.3 mM and 1.1 mM respectively, which were much lower than those of the xylose reductase from yeast. 相似文献
16.
17.
Nguyen Q. A. Tucker M. P. Boynton B. L. Keller F. A. Schell D. J. 《Applied biochemistry and biotechnology》1998,(1):77-87
Selective thinning of forests in the western United States will generate a large, sustainable quantity of softwood residues
that can be an attractive feedstock for fuel ethanol production. The major species available from thinning of forests in northern
California and the eastern Rocky Mountains include white fir (Abies concolor), Douglas fir (Pseudotsuga menziesii), and Ponderosa pine (Pinus ponderosa). Douglas fir chips were soaked in 0.4% sulfuric acid solution, then pretreated with steam at 200 – 230°C for 1 – 5 min.
After pretreatment, 90 – 95% of the hemicellulose and as much as 20% of the cellulose was solubilized in water, and 90% of
the remaining cellulose can be hydrolyzed to glucose by cellulase enzyme. The prehydrolysates, at as high as 10% total solid
concentration, can be readily fermented by the unadapted yeastSaccharomyces cerevisiae D5A. 相似文献
18.
Alcohol fuels produced from biomass can improve air quality, enhance energy security, create employment opportunities, and
reduce waste disposal problems. Opportunities in California exist to produce alcohols from waste streams from various sectors
of the economy. Government agencies have promoted waste-to-alcohol activities, but efforts have been inconsistent and intermittent.
Often these efforts have been hindered by contradictory but mandate-driven policies.
A prudent approach to coordinate statewide efforts includes the development of an integrated statewide policy to examine barriers
that impede private sector business efforts to produce alcohols from biomass. A multi-agency task force to promote research,
development, commercialization, and marketing efforts for biomass-produced alcohols is desirable.
The views and opinions contained in this document do not necessarily reflect those of the California Energy Commission, its
staff, management, or the State of California. 相似文献
19.
Based on this preliminary study, a metric ton of dry southern red oak chips subjected to a first-stage dilute sulfuric acid
hydrolysis would yield 132 kg of xylose and 40 kg of glucose and mannose. A second-stage dilute sulfuric acid hydrolysis on
the first-stage residue would yield only 128 kg of additional glucose, but a second-stage cellulytic enzyme hydrolysis on
the first-stage residue would yield an additional 265 kg of glucose. Fermentation of these hydrolyzates would show that the
hybrid process would yield over 50% more ethanol. Results on other biomass are also included. 相似文献
20.
The operational characterization of a fluidized-bed bioreactor for ethanol fermentation using Ca-alginate immobilized yeast
cells is described. An additional air stream is supplied to the fermenter to ensure and maintain satisfactory fluidization
behavior of beads and to avoid slug formation. The influence of physical properties such as bead density and liquid density
on the fluidization quality and stability are discussed. 相似文献