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1.
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
2.
Arabinose utilization by xylose-fermenting yeasts and fungi 总被引:1,自引:0,他引:1
Various wild-type yeasts and fungi were screened to evaluate their ability to fermentl-arabinose under oxygen-limited conditions when grown in defined minimal media containing mixtures ofl-ara-binose,d-xylose, andd-glucose. Although all of the yeasts and some of the fungi consumed arabinose, arabinose was not fermented to ethanol by any
of the strains tested. Arabitol was the only major product other than cell mass formed froml-arabinose; yeasts converted arabinose to arabitol at high yield. The inability to fermentl-arabinose appears to be a consequence of inefficient or incomplete assimilation pathways for this pentose sugar. 相似文献
3.
Donnelly Mark I. Millard Cynthia Sanville Clark David P. Chen Michael J. Rathke Jerome W. 《Applied biochemistry and biotechnology》1998,(1):187-198
Escherichia coli strain NZN111, which is unable to grow fermentatively because of insertional inactivation of the genes encoding pyruvate:
formate lyase and the fermentative lactate dehydrogenase, gave rise spontaneously to a chromosomal mutation that restored
its ability to ferment glucose. The mutant strain, named AFP111, fermented glucose more slowly than did its wild-type ancestor,
strain W1485, and generated a very different spectrum of products. AFP111 produced succinic acid, acetic acid, and ethanol
in proportions of approx 2:1:1. Calculations of carbon and electron balances accounted fully for the observed products; 1
mol of glucose was converted to 1 mol of succinic acid and 0.5 mol each of acetic acid and ethanol. The data support the emergence
in E.coli of a novel succinic acid:acetic acid:ethanol fermentation pathway. 相似文献
4.
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
5.
The potential market for lactic acid as the feedstock for biodegradable polymers, oxygenated chemicals, and specialty chemicals
is significant. L-lactic acid is often the desired enantiomer for such applications. However, stereospecific lactobacilli
do not metabolize starch efficiently. In this work, Argonne researchers have developed a process to convert starchy feedstocks
into L-lactic acid. The processing steps include starch recovery, continuous liquefaction, and simultaneous saccharification
and fermentation. Over 100 g/L of lactic acid was produced in less than 48 h. The optical purity of the product was greater
than 95%. This process has potential economical advantages over the conventional process. 相似文献
6.
The aim of preclarification is to minimize sludge going to yeast separators. This purpose is partially fulfilled. However,
it has been measured during the plant trial runs that preclarification does not noticeably improve fermentation.
The aim of postclarification is to minimize sludge going to distillation. This purpose is well served as noted from the fact
that cycle run of distillation columns using postclarification is three times longer (9–12 mo) as compared to the normal one
(3–4 mo). 相似文献
7.
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
8.
Ballesteros I. Ballesteros M. CabaÑas A. Carrasco J. MartÍn C. Negro M. J. Saez F. Saez R. 《Applied biochemistry and biotechnology》1991,(1):307-315
A total of 27 yeast strains belonging to the groupsCandida, Saccharomyces, andKluyveromyces were screened for their ability to grow and ferment glucose at temperatures ranging 32-45°C.
K. marxianus andK. fragilis were found to be the best ethanol producing organisms at the higher temperature tested and, so, were selected for subsequent
simultaneous saccharification and fermentation (SSF) studies. 相似文献
9.
Danner H. Neureiter M. Madzingaidzo L. Gartner M. Braun R. 《Applied biochemistry and biotechnology》1998,(1):895-903
A process for the continuous production of high purityL-lactic acid in a membrane bioreactor at 65°C has been developed. Two differentBacillus stearothermophilus strains have been tested in batch experiments. Lactic acid yields are between 60 and more than 95% of theoretical yields.
The amounts of ethanol, acetate, and formate formed varied between 0 and 0.4, 0 and 0.1, and 0 and 0.5, respectively (mol/mol
glucose). All byproducts are valuable and may be separated easily by rectification of the fermentation broth. Complete cell
retention enables high volumetric productivity (5 g/Lh), and a minimum of growth supplements. The high temperature of 65°C
allows the autoselective fermentation without problems with contamination. 相似文献
10.
Saha Badal C. Dien Bruce S. Bothast Rodney J. 《Applied biochemistry and biotechnology》1998,(1):115-125
Corn fiber, which consists of about 20% starch, 14% cellulose, and 35% hemicellulose, has the potential to serve as a low
cost feedstock for production of fuel ethanol. Currently, the use of corn fiber to produce fuel ethanol faces significant
technical and economic challenges. Its success depends largely on the development of environmentally friendly pretreatment
procedures, highly effective enzyme systems for conversion of pretreated corn fiber to fermentable sugars, and efficient microorganisms
to convert multiple sugars to ethanol. Several promising pretreatment and enzymatic processes for conversion of corn fiber
cellulose, hemicellulose, and remaining starch to fermentable sugars were evaluated. These hydrolyzates were then examined
for ethanol production in bioreactors, using genetically modified bacteria and yeast. Several novel enzymes were also developed
for use in pretreated corn fiber saccharification.
Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard
of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also
be suitable. 相似文献
11.
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
12.
Synthesis of Cyclodextrin Glucosyl Transferase byBacillus cereus for the production of cyclodextrins
R. Jamuna N. Saswathi R. Sheela S. V. Ramakrishna 《Applied biochemistry and biotechnology》1993,43(3):163-176
A potent indigenous bacillus isolate identified asBacillus cereus (RJ-30) was found to produce Cyclodextrin Glucosyl Transferase (CGTase) extracellularly. Process optimization of various
fermentation parameters has been established for optimal growth of bacillus and the maximum enzyme synthesis. The organism
had the highest specific growth rate (0.7μ) with a generation time of 1 h in glucose containing medium at the conditions of
pH 7.0, 37°C at 300 rpm, 1.5 vvm of agitation, and aeration. At these conditions, it exhibited the maximum activity of 54
U/mL at the synthesis rate of 2.7 U/L/h. CGTase was produced from the early exponential growth and peaked during the midsporulating
stage of about 16 h thereafter maintained at the same level of 50 U/mL. Saccharides containing media were better inducers
than starch, and the influence of carbohydrate substrates has shown that enzyme synthesis is promoted by xylose (65 U/mL)
and, more remarkably, by the supplementation of wheat bran extract in glucose medium (106 U/mL). This organism produced CGTase
stably in a chemostat culturing over a period of 400 h with a maximum productivity of 5.4 kU/L/h (threefold higher than obtained
in batch culturing [1.75 kU/L/h]). Comparatively, CGTase was produced by immobilized cells in a continuous fluidized bed reactor
for over approx 360 h, at a relatively high dilution rate of 0.88 h−1 resulting in the productivity of 23.0 kU/L/h. 相似文献
13.
14.
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
15.
L-Malate was produced from fumarate by using immobilized Saccharomyces cerevisiae cells entrapped in polyacrylamide. This preparation performed better when pretreated with malonate. Under the experimental conditions described here, succinate was not detected as a by-product of the reaction, as had been reported for other microorganisms. 相似文献
16.
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
17.
Chiang Heien-Kun Foutch Gary L. Fish Wayne W. 《Applied biochemistry and biotechnology》1991,(1):513-525
Acetaldehyde has been produced biologically using whole-cellPichia pastoris in a semibatch fermentor. Ethanol and air were fed continuously, and the product, acetaldehyde, was removed by the air stream.
Operation of the reactor exceeded 100 h, maintaining high alcohol oxidase activity. Low cell-mass concentration (9.9 g/L)
minimized product inhibition. Ethanol concentration in the broth, oxygen concentration in the air, and pH were evaluated for
their effects on the fermentation process. 相似文献
18.
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
19.
Succinic acid was produced efficiently from fumaric acid by a recombinantE. coli strain DH5αt/pGC1002 containing multicopy fumarate reductase genes. The effects of initial fumaric acid and glucose concentration
on the production of succinic acid were investigated. Succinic acid reached 41 to over 60 g/L in 48.5 h starting with 50 to
64 g/L fumaric acid. Significant substrate inhibition was observed at initial fumaric acid concentration of 90 g/L. L-Malic
acid became the major fermentation product under these conditions. Provision of glucose (5-30 g/L) to the fermentation medium
stimulated the initial succinic acid production rate over two folds. 相似文献
20.
Stenberg Kerstin Tengborg Charlotte Galbe Mats Zacchi Guido Palmqvist Eva Hahn-Hägerdal Bärbel 《Applied biochemistry and biotechnology》1998,(1):697-708
In ethanol production from lignocellulose by enzymatic hydrolysis and fermentation, it is desirable to minimize addition of
fresh-water and waste-water streams, which leads to an accumulation of substances in the process. This study shows that the
amount of fresh water used and the amount of waste water thereby produced in the production of fuel ethanol from softwood,
can be reduced to a large extent by recycling of either the stillage stream or part of the liquid stream from the fermenter.
A reduction in fresh-water demand of more than 50%, from 3 kg/kg dry raw material to 1.5 kg/kg dry raw material was obtained
without any negative effects on either hydrolysis or fermentation. A further decrease in the amount of fresh water, to one-fourth
of what was used without recycling of process streams, resulted in a considerable decrease in the ethanol productivity and
a slight decrease in the ethanol yield 相似文献