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1.
The inhibitory effects of pH and acetic acid on the co-fermentation of glucose and xylose in complex medium by recombinant flocculent Saccharomyces cerevisiae MA-R4 were evaluated. In the absence of acetic acid, the fermentation performance of strain MA-R4 was similar between pH?4.0?C6.0, but was negatively affected at pH?2.5. The addition of acetic acid to batch cultures resulted in negligible inhibition of several fermentation parameters at pH?6.0, whereas the interactive inhibition of pH and acetic acid on the maximum cell and ethanol concentrations, and rates of sugar consumption and ethanol production were observed at pH levels below 5.4. The inhibitory effect of acetic acid was particularly marked for the consumption rate of xylose, as compared with that of glucose. With increasing initial acetic acid concentration, the ethanol yield slightly increased at pH?5.4 and 6.0, but decreased at pH values lower than 4.7. Notably, ethanol production was nearly completely inhibited under low pH (4.0) and high acetic acid (150?C200?mM) conditions. Together, these results indicate that the inhibitory effects of acetic acid and pH on ethanol fermentation by MA-R4 are highly synergistic, although the inhibition can be reduced by increasing the medium pH. 相似文献
2.
Glucose/xylose mixtures (90 g/L total sugar) were evaluated for their effect on ethanol fermentation by a recombinant flocculent Saccharomyces cerevisiae, MA-R4. Glucose was utilized faster than xylose at any ratio of glucose/xylose, although MA-R4 can simultaneously co-ferment both sugars. A high percentage of glucose can increase cell biomass production and therefore increase the rate of glucose utilization (1.224 g glucose/g biomass/h maximum) and ethanol formation (0.493 g ethanol/g biomass/h maximum). However, the best ratio of glucose/xylose for the highest xylose consumption rate (0.209 g xylose/g biomass/h) was 2:3. Ethanol concentration and yield increased and by-product (xylitol, glycerol, and acetic acid) concentration decreased as the proportion of glucose increased. The maximum ethanol concentration was 41.6 and 21.9 g/L after 72 h of fermentation with 90 g/L glucose and 90 g/L xylose, respectively, while the ethanol yield was 0.454 and 0.335 g/g in 90 g/L glucose and 90 g/L xylose media, respectively. High ethanol yield when a high percentage of glucose is available is likely due to decreased production of by-products, such as glycerol and acetic acid. These results suggest that ethanol selectivity is increased when a higher proportion of glucose is available and reduced when a higher proportion of xylose is available. 相似文献
3.
Different initial cell concentrations of a recombinant flocculent Saccharomyces cerevisiae MA-R4 were evaluated for their effects on xylose fermentation and glucose–xylose cofermentation. A high initial cell concentration greatly increased both the substrate utilization and ethanol production rates. During xylose fermentation, the highest rates of xylose consumption (2.58 g/L h) and ethanol production (0.83 g/L h) were obtained at an initial cell concentration of 13.1 g/L. During cofermentation, the highest rates of glucose consumption (14.4 g/L h), xylose consumption (2.79 g/L h), and ethanol production (6.68 g/L h) were obtained at an initial cell concentration of 12.7 g/L. However, a high initial cell density had no positive effect on the maximum ethanol concentration and ethanol yield mainly due to the increased amount of by-products including xylitol. The ethanol yield remained almost constant (0.34 g/g) throughout xylose fermentation (initial cell concentration range, 1.81–13.1 g/L), while it was slightly lower at high initial cell concentrations (9.87 and 12.7 g/L) during cofermentation. The determination of the appropriate initial cell concentration is necessary for the improvement of substrate utilization and ethanol yield. 相似文献
4.
For optimum fermentation, fermenting xylose into acetic acid by Clostridium thermoaceticum (ATCC 49707) requires adaptation of the strain to xylose medium. Exposed to a mixture of glucose and xylose, it preferentially
consumesxylose over glucose. The initial concentration of xylose in the medium affects the final concentration and the yield
of acetic acid. Batch fermentation of 20 g/L of xylose with 5g/L of yeast extract as the nitrogen source results in a maximum
acetate concentration of 15.2 g/L and yield of 0.76 g of acid/g of xylose. Corn steep liquor (CLS) is a good substitute for
yeast extract and results in similar fermentation profiles. The organism consumes fructose, xylose, and glucose from a mixture
of sugars in batch fermentation. Arabinose, mannose, and galactose are consumed only slightly. This organism loses viability
on fed-batch operation, even with supplementation of all the required nutrients. In fed-batch fermentation with CSL supplementation,
d-xylulose (an intermediate in the xylose metabolic pathway) accumulates in large quantities. 相似文献
5.
The influence of other hemicellulosic sugars (arabinose, galactose, mannose, and glucose), oxygen limitation, and initial
xylose concentration on the fermentation of xylose to xylitol was in vestigated using experimental design methodology. Oxygen
limitation and initial xylose concentration had strong influences on xylitol production by Candida tropicalis ATCC 96745. Under semiaerobic conditions, xylitol yield was highest (0.62 g/g), whereas under aerobic conditions volumetric
productivity was highest (0.90g/[L·h]). In the presence of glucose, xylose utilization was strongly repressed and sequential
sugar utilization was observed. Ethanol produced from the glucose caused a 50% reduction in xylitol yield when the ethanol
con centration exceeded 30 g/L. When complex synthetic hemicellulosic sugars were fermented, glucose was initially consumed
followed by a simultaneous uptake of the other sugars. The highest xylitol yield (0.84 g/g) and volumetric productivity (0.49
g/[L·h]) were obtained for substrates containing high arabinose and low glucose and mannose contents. 相似文献
6.
Fermentation kinetics of ethanol production from glucose, xylose, and their mixtures using a recombinant Saccharomyces 1400 (pLNH33) are reported. Single-substrate kinetics indicate that the specific growth rate of the yeast and the specific
ethanol productivity on glucose as the substrate was greater than on xylose as a substrate. Ethanol yields from glucose and
xylose fermentation were typically 95 and 80% of the theoretical yield, respectively. The effect of ethanol inhibition is
more pronounced for xylose fermentation than for glucose fermentation. Studies on glucose-xylose mixtures indicate that the
recombinant yeast co-ferments glucose and xylose. Fermentation of a 52.8 g/L glucose and 56.3 g/L xylose mixture gave an ethanol
concentration of 47.9 g/L after 36 h. Based on a theoretical yield of 0.51 g ethanol/g sugars, the ethanol yield from this
experiment (for data up to 24 h) was calculated to be 0.46 g ethanol/g sugar or 90% of the theoretical yield. The specific
growth rate of the yeast on glucose-xylose mixtures was found to lie between the specific growth rate on glucose and the specific
growth rate on xylose. Kinetic studies were used to develop a fermentation model incorporating the effects of substrate inhibition,
product inhibition, and inoculum size. Good agreements were obtained between model predictions and experimental data from
batch fermentation of glucose, xylose, and their mixtures. 相似文献
7.
Xylose-fermenting recombinant Zymomonas mobilis has been proposed as a candidate biocatalyst for the production of fuel ethanol from cellulosic biomass and wastes. This study documents the effect of glucose on xylose utilization by recombinant Z. mobilis CP4:pZB5 using a nutrient-rich synthetic (puresugar) hardwood dilute-acid prehydrolyzate medium containing 0.8% (w/v) glucose and 4% (w/v) xylose that was enriched with respect to xylose concentration within the range 6–10% (w/v) xylose. Supplementation with glucose toafinal concentration of 2% (w/v) resulted in faster xylose utilization of both 6% and 8% xylose; however, higher levels of glucose supplementation (>2%) did not result in a decrease in the time required for fermentation of either 6% or 8% xylose. An improvement in the rate of 8% xylose utilization was also achieved through, continuous glucose feeding in which the total glucose concentration was about 1.3% (w/v). This fedbatch experiment was designed to mimic the continuous supply of glucose provided by the cellulose saccharifying enzymes in a simultaneous saccharifying and cofermentation process. The upper limit ethanol concentration at which xylose utilization by recombinant Z. mobilis CP4:pZB5 is completely inhibited is about 5.5% (w/v) at pH 5 and >6% at pH 5.75. At pH 5.75, this level of ethanol was achieved with the following media of pure sugar mixtures (each containing the same sugar loading of 12% (w/v): - 6% xylose+6% glucose;
- 8% xylose+4% glucose; and
- 4% xylose+8% glucose.
At the level of inoculum used in this study, complete fermentation of the 12% sugar mixtures required 2–3 d (equivalent to a volumetric ethanol productivity of 0.83–1.25 g ethanol/L.h). The sugar-to-ethanol conversion efficiency was 94–96% of theoretical maximum. 相似文献
8.
采用乙醇分级沉淀法,首次从野生菱角壳中提取出4种多糖化合物,利用气相色谱-质谱法,确定了菱角多糖分别由阿拉伯糖,鼠李糖,木糖,甘露糖,半乳糖,葡萄糖,乳糖和蜜二糖组成,其中以葡萄糖,半乳糖,甘露糖和木糖为主。 相似文献
9.
Lactobacillus species capable of fermenting glucose are generally incapable of utilizing xylose for growth or fermentation. In this study,
a novel aspect of a well-known Lactobacillus strain, L. casei subsp. rhamnous (ATCC 10863), was uncovered: it can ferment xylose as efficiently as glucose. This strain is a registered organism, extremely
stable on long-term operation. Fermentation by this strain is characterized by an initial lag phase lasting 24–72 h before
xylose consumption takes place. The yield (grams/gram) of lactic acid from xylose is in excess of 80% with initial volumetric
productivity of 0.38 g/(L-h). Acetic acid is the primary byproduct formed at the level of about 10% of the lactic acid. In
addition to xylose, it can ferment all other minor sugars in hemicellulose except arabinose. Subjected to mixed sugar fermentation,
this strain consumes glucose first, then mannose, followed by almost simultaneous utilization of xylose and galactose. It
shows high tolerance for lactic acid as well as extraneous toxins. It can ferment the mixed sugars present in acid-treated
hydrolysate of softwood, giving yields similar to that of pure sugar but at a slower rate.
Author to whom all correspondence and reprint requests should be addressed. 相似文献
10.
报道了测定多糖中单糖组成的糖醇乙酸酯的毛细管气相色谱分析方法。使用OV-225毛细管气相色谱柱分离了11种单糖的糖醇乙酸酯衍生物,在0.2~1.68g/L质量浓度范围内,11种单糖定量校正曲线的线性关系廊。应用该法测定了胡麻我发多糖和少 我中单糖的组成。为这些药物多糖的基础研究提供了有用的信息。 相似文献
11.
Multiple linear regression analysis was used to deduce the correlation between the monosaccharide composition ratios of 10 regionally different strains of Lentinula edodes and their in vitro macrophage stimulatory activities. Arabinose, xylose, mannose and galactose were identified as the monosaccharides that could be related to macrophage stimulatory activities. Additional principal component analysis and factor analysis methods were used to treat the same monosaccharide composition ratio data and the compositions of arabinose, xylose, mannose and galactose were found to be important. Interestingly, glucose, although presented in large compositions in all strains presumably forms the backbone of the polysaccharide structures, is not selected as the determinant factor for either structural characteristics or that of the in vitro macrophage stimulatory activities. 相似文献
12.
In the production of ethanol from lignocellulosic biomass, the hydrolysis of the acetylated pentosans in hemicellulose during pretreatment produces acetic acid in the prehydrolysate. The National Renewable Energy Laboratory (NREL) is currently investigating a simultaneous saccharification and cofermentation (SSCF) process that uses a proprietary metabolically engineered strain ofZymomonas mobilis that can coferment glucose and xylose. Acetic acid toxicity represents a major limitation to bioconversion, and cost-effective means of reducing the inhibitory effects of acetic acid represent an opportunity for significant increased productivity and reduced cost of producing fermentation fuel ethanol from biomass. In this study, the fermentation performance of recombinant Z.mobilis 39676:pZB4L, using a synthetic hardwood prehydrolysate containing 1% (w/v) yeast extract, 0.2% KH2PO4, 4% (w/v) xylose, and 0.8% (w/v) glucose, with varying amounts of acetic acid was examine. To minimize the concentration of the inhibitory undissociated form of acetic acid, the pH was controlled at 6.0. The final cell mass concentration decreased linearly with increasing level of acetic acid over the range 0-0.75% (w/v), with a 50% reduction at about 0.5% (w/v) acetic acid. The conversion efficiency was relatively unaffected, decreasing from 98 to 92%. In the absence of acetic acid, batch fermentations were complete at 24 h. In a batch fermentation with 0.75% (w/v) acetic acid, about two-thirds of the xylose was not metabolized after 48 h. In batch fermentations with 0.75% (w/v) acetic acid, increasing the initial glucose concentration did not have an enhancing effect on the rate of xylose fermentation. However, nearly complete xylose fermentation was achieved in 48 h when the bioreactor was fed glucose. In the fed-batch system, the rate of glucose feeding (0.5 g/h) was designed to simulate the rate of cellulolytic digestion that had been observed in a modeled SSCF process with recombinant Zymomonas. In the absence of acetic acid, this rate of glucose feeding did not inhibit xylose utilization. It is concluded that the inhibitory effect of acetic acid on xylose utilization in the SSCF biomass-to-ethanol process will be partially ameliorated because of the simultaneous saccharification of the cellulose. 相似文献
13.
The synthesis and structure-activity relationships of a new series of indolo[2,3- a]carbazole glycosides, analogs of rebeccamycin, derived from the natural sugars (glucose, fucose, mannose, xylose, rhamnose, and galactose) is described. 相似文献
14.
A mutant Cs3512, which showed better fermentation of xylose and the mixtures of xylose and glucose, was obtained through mutation
of Candida shehatae ATCC 22984 and screening with a medium containing antimycin A and TTC (2,3,5-triphenyltetrazolium chloride). Cs3512 produced
44.4 g/l of ethanol from 121.3 g/l of xylose, which was 13% higher than that by ATCC 22984. At the same time, xylitol production
was reduced by 38% to 10.2 g/l from 16.3 g/l by ATCC 22984. Cs3512 also showed 8% increase in ethanol yield from 0.39 to 0.42 g/g
comparing to ATCC 22984 when fermenting the sugar mixture composed of 52.9 g/l glucose and 21.2 g/l xylose. When Cs3512 was
used in the simultaneous saccharification and fermentation of lime pretreated rice straw via CaCCO (calcium capturing by carbonation)
process, it produced ethanol at 77% of the theoretical yield. The results imply that Cs3512 is a potential non-recombinant
yeast strain for ethanol production from lignocellulosic biomass. 相似文献
15.
Recent studies have proven ethanol to be the idael liquid fuel for transportation, and renewable ligno cellulosic materials
to be the attractive feed stocks for ethanol fuel production by fermentation. The major fermentable sugars from hydrolysis
of most cellulosic biomass are D-glucose and D-xylose. The naturally occurring Saccharomyces yeasts that are used by industry to produce ethanol from starches and cane sugar cannot metabolize xylose. Our group at Purdue
University succeded in developing genetically engineered Saccharomyces yeasts capable of effectively cofermenting glucose and xylose to ethanol, which was accomplished by cloning three xylose-metabolizing
genes into the yeast. In this study, we demonstrated that our stable recombinant Sacharomyces yeast, 424A (LNH-ST), which contains the cloned xylose-metabolizing genes stably integrated into the yeast chromosome in
high copy numbers, can efficiently ferment glucose and xylose present in hydrolysates from different cellulosic biomass to
ethanol. 相似文献
16.
Of the sugars recovered from lignocellulose, d-glucose can be readily converted into ethanol by baker’s or brewer’s yeast ( Saccharomyces cerevisiae). However, xylose that is obtained by the hydrolysis of the hemicellulosic portion is not fermentable by the same species
of yeasts. Xylose fermentation by native yeasts can be achieved via isomerization of xylose to its ketose isomer, xylulose.
Isomerization with exogenous xylose isomerase (XI) occurs optimally at a pH of 7–8, whereas subsequent fermentation of xylulose
to ethanol occurs at a pH of 4–5. We present a novel scheme for efficient isomerization of xylose to xylulose at conditions
suitable for the fermentation by using an immobilized enzyme system capable of sustaining two different pH microenvironments
in a single vessel. The proof-of-concept of the two-enzyme pellet is presented, showing conversion of xylose to xylulose even
when the immobilized enzyme pellets are suspended in a bulk solution whose pH is sub-optimal for XI activity. The co-immobilized
enzyme pellets may prove extremely valuable in effectively conducting “simultaneous isomerization and fermentation” (SIF)
of xylose. To help further shift the equilibrium in favor of xylulose formation, sodium tetraborate (borax) was added to the
isomerization solution. Binding of tetrahydroxyborate ions to xylulose effectively reduces the concentration of xylulose and
leads to increased xylose isomerization. The formation of tetrahydroxyborate ions and the enhancement in xylulose production
resulting from the complexation was studied at two different bulk pH values. The addition of 0.05 M borax to the isomerization
solution containing our co-immobilized enzyme pellets resulted in xylose to xylulose conversion as high as 86% under pH conditions
that are suboptimal for XI activity. These initial findings, which can be optimized for industrial conditions, have significant
potential for increasing the yield of ethanol from xylose in an SIF approach. 相似文献
17.
Fermentative hydrogen production is strongly affected by pH. In order to maximize hydrogen production and substrate consumption in Escherichia coli Δ hycA, Δ lacI (WDHL) cheese whey fermentation, the influence of pH control at values of 5.5, 6, and 6.5 was studied in batch stirred-tank bioreactors. From the conditions evaluated, pH 6.5 was the best condition, at which the highest cumulative hydrogen production and yield (1.78 mol H 2/mol lactose) were obtained. Moreover, at this pH, all carbohydrates from the cheese whey were consumed, and a mix of ethanol and organic acids, mainly lactate, were produced from glucose, whereas galactose yielded acetate, ethanol, and succinate. Operating the reactor at pH 5.5 resulted in the highest maximum specific production rate, but smaller hydrogen yield because only glucose was metabolized and galactose was accumulated. At pH 6, not all cheese whey carbohydrates were consumed, and it was not favorable for hydrogen production. Lactose consumption and growth kinetics were not affected by the pH. The results show the importance of controlling pH to maximize hydrogen production and substrate consumption using cheese whey as substrate. 相似文献
18.
Mixed fungal cultures used for making tempe, a fermented soy bean food, were screened for biomass conversion. Thirty-two zygomycetes strains from two tempe cultures were isolated and identified as Rhizopus, Mucor, Rhizomucor, and Absidia species based upon morphology. The dry weight biomass of these strains contained 49% to 63% protein and 10?C24% chitosan. The strains with the best growth performance were selected and registered at Culture Collection of Gothenburg University as Rhizomucor CCUG 61146 and Rhizomucor CCUG 61147. These strains were able to grow both aerobically and micro-aerobically. Their ethanol yields were 0.38?C0.47, 0.19?C0.22, and 0.31?C0.38?g/g on glucose, xylose, and a mix sugars consisting of cellobiose, glucose, xylose, arabinose, galactose, and mannose, respectively. The biomass yield of the strains varied between 65 and 140?mg dry weight/g glucose. 相似文献
19.
The fermentation characteristics of two recombinant strains of Zymomonas mobilis, viz. CP4 (pZB5) and ZM4 (pZB5), capable of converting both glucose and xylose to ethanol, have been characterized in batch
and continuous culture studies. The strain ZM4 (pZB5) was found to be capable of converting a mixture of 65 g/L glucose and
65 g/L xylose to 62 g/L ethanol in 48h with a yield of 0.46 g/g. Higher sugar concentrations resulted in incompletexylose
utilization (80h) presumably owing to ethanol inhibition of xylose assimilation or metabolism. The fermentation results with
ZM4 (pZB5) show a significant improvement over results published previously for recombinant yeasts and other bacteria capable
of glucose and xylose utilization. 相似文献
20.
The five-carbon sugar d-xylose is a major component of hemicellulose and accounts for roughly one-third of the carbohydrate content of many lignocellulosic
materials. The efficient fermentation of xylose-rich hemicellulose hydrolyzates (prehydrolyzates) represents an opportunity
to improve significantly the economics of large-scale fuel ethanol production from lignocellulosic feedstocks. The National
Renewable Energy Laboratory (NREL) is currently investigating a simultaneous saccharification and cofermentation (SSCF) process
for ethanol production from biomass that uses a dilute-acid pretreatment and a metabolically engineered strain of Zymomonas mobilis that can coferment glucose and xylose. The objective of this study was to establish optimal conditions for cost-effective
seed production that are compatible with the SSCF process design.
Two-level and three-level full factorial experimental designs were employed to characterize efficiently the growth performance
of recombinant Z. mobilis CP4:pZB5 as a function of nutrient level, pH, and acetic acid concentration using a synthetic hardwood hemicellulose hydrolyzate
containing 4% (w/v) xylose and 0.8% (w/v) glucose. Fermentations were run batchwise and were pH-controlled at low levels of
clarified corn steep liquor (cCSL, 1-2% v/v), which were used as the sole source of nutrients. For the purpose of assessing
comparative fermentation performance, seed production was also carried out using a “benchmark” yeast extract-based laboratory
medium. Analysis of variance (ANOVA) of experimental results was performed to determine the main effects and possible interactive
effects of nutrient (cCSL) level, pH, and acetic acid concentration on the rate of xylose utilization and the extent of cell
mass production. Results indicate that the concentration of acetic acid is the most significant limiting factor for the xylose
utilization rate and the extent of cell mass production; nutrient level and pH exerted weaker, but statistically significant
effects. At pH 6.0, in the absence of acetic acid, the final cell mass concentration was 1.4 g dry cell mass/L (g DCM/L),
but decreased to 0.92 and 0.64 g DCM/L in the presence of 0.5 and 1.0% (w/v) acetic acid, respectively. At concentrations
of acetic acid of 0.75 (w/v) or lower, fermentation was complete within 1.5 d. In contrast, in the presence of 1.0% (w/v)
acetic acid, 25% of the xylose remained after 2 d. At a volumetric supplementation level of 1.5–2.0% (v/v), cCSL proved to
be a cost-effective single-source nutritional adjunct that can support growth and fermentation performance at levels comparable
to those achieved using the expensive yeast extract-based laboratory reference medium. 相似文献
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