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1.
The kinetics of P. acidipropionici (ATCC25562), a xylose-utilizing rumen microorganism, was studied to assess its use for propionic acid production from wood
hydrolyzates.
Propionic acid has been shown to have a stronger inhibitory effect than acetic acid, with the undissociated acid form being
responsible for the majority of the inhibitory effect. Thus, in batch tests with pH controlled at 6.0, the propionic acid
concentration reaches 25 g/L and the acetic acid 7 g/L. Xylose uptake rate is dependent on the specific growth rate and glucose
concentration.
An immobilized cell columnar reactor at very high product yields (80%) proved adequate for propionic production. At cell concentrations
of 95 g/L with high product concentration, volumetric productivities of 2.7 g/L·h were obtained in ultrafiltration cell recycle
systems. 相似文献
2.
Lactic acid is an important product arising from the anaerobic fermentation of sugars. It is used in the pharmaceutical, cosmetic, chemical, and food industries as well as for biodegradable polymer and green solvent production. In this work, several bacterial strains were isolated from industrial ethanol fermentation, and the most efficient strain for lactic acid production was selected. The fermentation was conducted in a batch system under anaerobic conditions for 50 h at a temperature of 34 °C, a pH value of 5.0, and an initial sucrose concentration of 12 g/L using diluted sugarcane molasses. Throughout the process, pulses of molasses were added in order to avoid the cell growth inhibition due to high sugar concentration as well as increased lactic acid concentrations. At the end of the fermentation, about 90% of sucrose was consumed to produce lactic acid and cells. A kinetic model has been developed to simulate the batch lactic acid fermentation results. The data obtained from the fermentation were used for determining the kinetic parameters of the model. The developed model for lactic acid production, growth cell, and sugar consumption simulates the experimental data well. 相似文献
3.
The economics of large-scale production of fuel ethanol from biomass and wastes requires the efficient utilization of all
the sugars derived from the hydrolysis of the heteropolymeric hemicellulose component of lignocellulosic feedstocks. Glucuronic
and 4-0-methyl-glucuronic acids are major side chains in xylans of the grasses and hardwoods that have been targeted as potential
feedstocks for the production of cellulosic ethanol. The amount of these acids is similar to that of arabinose, which is now
being viewed as another potential substrate in the production of biomass-derived ethanol.
This study compared the end-product distribution associated with the fermentation of D-glucose (Glc) and D-glucuronic acid
(GlcUA) (as sole carbon and energy sources) by Escherichia coli B (ATCC 11303) and two different ethanologenic recombinants—a strain in which pet expression was via a multicopy plasmid (pLOI297) and a chromosomally integrated construct, strain KO11. pH-stat batch fermentations
were conducted using a modified LB medium with 2% (w/v) Glc or GlcUA with the set-point for pH control at either 6.3 or 7.0.
The nontransformed host culture produced only lactic acid from glucose, but fermentation of GlcUA yielded a mixture of ethanol,
acetic, and lactic acids, with acetic acid being the predominant end-product. The ethanol yield associated with GlcUA fermentation
by both recombinants was similar, but acetic acid was a significant by-product. Increasing the pH from 6.3 to 7.0 increased
the rate of glucuronate fermentation, but it also decreased the ethanol mass yield from 0.22 to 0.19 g/g primarily because
of an increase in acetic acid production. In all fermentations there was good closure of the carbon mass balance, the exception
being the recombinant bearing plasmid pLOI297 that produced an unidentified product from GlcUA. The metabolism of GlcUA by
this metabolically engineered construct remains unresolved. The results offered insights into metabolic fluxes and the regulation
of pyruvate catabolism in the wild-type and engineered strains. End-product distribution for metabolism of glucuronic acid
by the nontransformed, wild-type E. coli B and recombinant strain KO11 suggests that the enzyme pyruvate-formate lyase is not solely responsible for the production
of acetylCoA from pyruvate and that derepressed pyruvate dehydrogenase may play a significant role in the metabolism of GlcUA. 相似文献
4.
Two distinctive forms of growth (mycelial filamentous and mycelial pellets) of Rhizopus oryzae were obtained by manipulating the initial pH of the medium with the controlled addition of CaCO 3 in a bubble fermenter. In the presence of CaCO 3, diffused filamentous growth was obtained when the initial pH of the substrate was 5.5. In the absence of CaCO3, mycelial
pellet growth was obtained when the initial pH was 2.0. The fermentation study indicated that the mycelial growth has a shorter
lag period before the onset of acid formation. Both physical forms of growth of Rhizopus exhibited a high yield of L-lactic acid in the bubble fermenter when the initial glucose concentration exceeded 70 g/L. A
final lactic acid concentration of 62 g/L was produced by the filamentous form of Rhizopus from 78 g/L glucose after 27 h. This showed a weight yield of 80% of glucose consumed, with an average specific productivity
of 1.46 g/h/g. Similarly, the pellet form of Rhizopus produced a final lactic acid concentration of 66 g/L from 76 g/L glucose after 43 h, with a weight yield of 86% and an average
specific productivity of 1.53 g/h/g. 相似文献
5.
The fermentative production of lactic acid from cheese whey and corn steep liquor (CSL) as cheap raw materials was investigated
by using Lactobacillus sp. RKY2 in order to develop a cost-effective fermentation medium. Lactic acid yields based on consumed lactose were obtained
at more than 0.98 g/g from the medium containing whey lactose. Lactic acid productivities and yields obtained from whey lactose
medium were slightly higher than those obtained from pure lactose medium. The lactic acid productivity gradually decreased
with increase in substrate concentration owing to substrate and product inhibitions. The fermentation efficiencies were improved
by the addition of more CSL to the medium. Moreover, through the cell-recycle repeated batch fermentation, lactic acid productivity
was maximized to 6.34 g/L/h, which was 6.2 times higher than that of the batch fermentation. 相似文献
6.
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
7.
In pH-controlled batch fermentations with pure sugar synthetic hardwood hemicellulose (1% [w/v] glucose and 4% xylose) and
corn stover hydrolysate (8% glucose and 3.5% xylose) lacking acetic acid, the xyloseutilizing, tetracycline (Tc)-sensitive,
genomically integrated variant of Zymomonas mobilis ATCC 39676 (designated strain C25) exhibited growth and fermentation performance that was inferior to National Renewable
Energy Laboratory's first-generation, Tc-resistant, plasmid-bearing Zymomonas recombinants. With C25, xylose fermentation following glucose exhaustion wasmarkellyslower, and the ethanol yield (based
on sugars consumed) was lower, owing primarily to an increase in lactic acid formation. There was an apparent increased sensitivity
to acetic acid inhibition with C25 compared with recombinants 39676:pZB4L, CP4:pZB5, and ZM4:pZB5. However, strain C25 performed
well in continous ferm entation with nutrient-rich synthetic corn stover medium over the dilution range 0.03–0.06/h, with
a maximum provess ethanol yield at D=0.03/h of 0.46 g/g and a maximum ethanol productivity of 3 g/(L·h). With 0.35% (w/v) acetic acid in the medium, the process
yield at D=0.04/h dropped to 0.32 g/g, and the maximum productivity decreased by 50% to 1.5 g/(L·h). Under the same operating conditions,
rec Zm Zm 4:pZB5 performed better; however, the medium contained 20 mg/L of Tc to constantly maintain selective pressure.
The absence of any need for antibiotics and antiboitic resistance genes makes the chromosomal integrant C25 more com patible
with current regulatory specifications for biocatalysts in large-scale commercial operations. 相似文献
8.
The fermentative production of lactic acid from cheese whey and corn steep liquor (CSL) as cheap raw materials was investigated by using Lactobacillus sp. RKY2 in order to develop a cost-effective fermentation medium. Lactic acid yields based on consumed lactose were obtained at more than 0.98 g/g from the medium containing whey lactose. Lactic acid productivities and yields obtained from whey lactose medium were slightly higher than those obtained from pure lactose medium. The lactic acid productivity gradually decreased with increase in substrate concentration owing to substrate and product inhibitions. The fermentation efficiencies were improved by the addition of more CSL to the medium. Moreover, through the cell-recycle repeated batch fermentation, lactic acid productivity was maximized to 6.34 g/L/h, which was 6.2 times higher than that of the batch fermentation. 相似文献
9.
This study documents the similar pH-dependent shift in pyruvate metabolism exhibited by Zymomonas mobilis ATCC 29191 and ATCC 39676 in response to controlled changes in their steady-state growth environment. The usual high degree
of ethanol selectivity associated with glucose fermentation by Z. mobilis is associated with conditions that promote rapid and robust growth, with about 95% of the substrate (5% w/v glucose) being
converted to ethanol and CO 2, and the remaining 5% being used for the synthesis of cell mass. Conditions that promote energetic uncoupling cause the conversion
efficiency to increase to 98% as a result of the reduction in growth yield (cell mass production). Under conditions of glucose-limited
growth in a chemostat, with the pH controlled at 6.0, the conversion efficiency was observed to decrease from 95% at a specific
growth rate of 0.2/h to only 80% at 0.042/h. The decrease in ethanol yield was solely attributable to the pH-dependent shift
in pyruvate metabolism, resulting in the production of lactic acid as a fermentation byproduct. At a dilution rate (D) of
0.042/h, decreasing from pH 6.0 to 5.5 resulted in a decrease in lactic acid from 10.8 to 7.5 g/L. Lactic acid synthesis depended
on the presence of yeast extract (YE) or tryptone in the 5% (w/v) glucose-mineral salts medium. At D = 0.15/h, reduction in
the level of YE from 3 to 1 g/L caused a threefold decrease in the steady-state concentration of lactic acid at pH 6. No lactic
acid was produced with the same mineral salts medium, with ammonium chloride as the sole source of assimilable nitrogen. With
the defined salts medium, the conversion efficiency was 98% of theoretical maximum. When chemostat cultures were used as seed
for pH-stat batch fermentations, the amount of lactic acid produced correlated well with the activity of the chemostat culture;
however, the mechanism of this prolonged induction 相似文献
10.
Xylose is the major pentose and the second most abundant sugar in lignocellulosic feedstock. Its efficient utilization is regarded as a technical barrier to the commercial production of bulk chemicals from lignocellulosic biomass. This work aimed at evaluating the lactic acid production from the biomass-derived xylose using non-sterilized fermentation by Bacillus coagulans NL01. A maximum lactic acid concentration of about 75 g/L was achieved from xylose of 100 g/L after 72 h batch fermentation. Acetic acid and levulinic acid were identified as important inhibitors in xylose fermentation, which markedly reduced lactic acid productivity at 15 and 1.0 g/L, respectively. But low concentrations of formic acid (<2 g/L) exerted a stimulating effect on the lactic acid production. When prehydrolysate containing total 25.45 g/L monosaccharide was fermented with B. coagulans NL01, the same preference for glucose, xylose, and arabinose was observed and18.2 g/L lactic acid was obtained after 48 h fermentation. These results proved that B. coagulans NL01 was potentially well-suited for producing lactic acid from underutilized xylose-rich prehydrolysates. 相似文献
11.
Propionic acid (PA) is widely used as additive in animal feed and also in the manufacturing of cellulose-based plastics, herbicides, and perfumes. Salts of propionic acid are used as preservative in food. PA is mainly produced by chemical synthesis. Nowadays, PA production by fermentation of low-cost industrial wastes or renewable sources has been an interesting alternative. In the present investigation, PA production by Propionibacterium acidipropionici ATCC 4965 was studied using a basal medium with sugarcane molasses (BMSM), glycerol or lactate (BML) in small batch fermentation at 30 and 36 degrees C. Bacterial growth was carried out under low dissolved oxygen concentration and without pH control. Results indicated that P. acidipropionici produced more biomass in BMSM than in other media at 30 degrees C (7.55 g l(-1)) as well as at 36 degrees C (3.71 g l(-1)). PA and biomass production were higher at 30 degrees C than at 36 degrees C in all cases studied. The best productivity was obtained by using BML (0.113 g l(-1) h(-1)), although the yielding of this metabolite was higher when using glycerol as carbon source (0.724 g g(-1)) because there was no detection of acetic acid. By the way, when using the other two carbon sources, acetic acid emerged as an undesirable by-product for further PA purification. 相似文献
12.
The production of lactic acid from glucose has been demonstrated using a CSTR (continuous stirred-tank reactor) with cell
recycle. Studies were conducted with Lactobacillus delbrueckii at a fermentation temperature of 42°C and a pH of 6.25. A cell density of 140 g dry weight/L and a volumetric productivity
of 150 g/L.h, with complete glucose consumption, were obtained. It was not possible to obtain a lactic acid concentration
above 60 g/L because of product inhibition. A cell purge was not necessary to maintain high viability bacteria culture or
to obtain a steady state. At steady state the net cell growth appeared to be negligible. The specific glucose consumption
for cell maintenance was 0.33 g glucose/g cells-h. 相似文献
13.
The hydrolysis process on corncob residue was catalyzed synergetically by the cellulase from Trichoderma reesei and the immobilized cellobiase. The feedback inhibition to cellulase reaction caused by the accumulation of cellobiose was
eliminated efficiently. The hydrolysis yield of corncob residue was 82.5%, and the percentage of glucose in the reducing sugar
reached 88.2%. The glucose in the cellulosic hydrolysate could be converted into lactic acid effectively by the immobilized
cells of Lactobacillus delbrueckii. When the enzymatic hydrolysis of cellulose and the fermentation of lactic acid were coupled together, no glucose was accumulated
in the reaction system, and the feedback inhibition caused by glucose was also eliminated. Under the batch process of synergetic
hydrolysis and lactic acid fermentation with 100 g/L of cellulosic substrate, the conversion efficiency of lactic acid from
cellulose and the productivity of lactic acid reached 92.4% and 0.938 g/(L·h), respectively. By using a fed-batch technique,
the total concentration of cellulosic substrate and lactic acid in the synergetic process increased to 200 and 107.5 g/L,
respectively, whereas the dosage of cellulase reduced from 20 to 15 IU/g of substrate in the batch process. The results of
the bioconversion of renewable cellulosic resources were significant. 相似文献
14.
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
15.
Escherichia coli KO11, in which the genes pdc (pyruvate decarboxylase) and adh (alcohol dehydrogenase) encoding the ethanolpathway from Zymomonas mobili were inserted into the chromosome, has been shown to metabolize all major sugars that are consituents of hemicellulosic hydrolysates
to ethanol, in anaerobic conditions. However, the growth and fermentation performance of this recombinant bacteria may be
affected by acetic acid a potential inhibitor present in hemicellulose hydrolysates in a range of 2.0–15.0 g/L. It was observed
that acetate affected the growth of E. coli KO11, prolonging the lag phase and inducing loss of biomass production and reduction of growth rate. At lower pH levels,
the sensitivity to acetic acid was enhanced owing to the increased concentration of the protonated species. On the other hand,
the recombinant bacteria showed a high tolerance to acetic acid regarding fermentative performance. In Luria broth medium
with glucose or xylose as a single sugar source, it was observed that neither yield nor productivity was affected by the addition
of acetate in a range of 2.0–12.0 g/L, suggesting some uncoupling of the growth vs ethanol production. 相似文献
16.
The production of propionic acid by Propionibacterium freudenreichii CCTCC M207015 was investigated in a 7.5-l stirred-tank fermentor. Batch fermentations by P. freudenreichii CCTCC M207015 at various pH values ranging from 5.5 to 7.0 were studied. Based on the analysis of the time course of specific
cell growth rate ( μ
x) and specific propionic acid formation rate ( μ
p), a two-stage pH-shift control strategy was proposed. At first 48 h, pH was controlled at 6.5 to obtain the maximal μ
x, subsequently pH 6.0 was used to maintain high μ
p to enhance the production of propionic acid. By applying this pH-shift control strategy in propionic acid fermentation, the
maximal propionic acid and glucose conversion efficiency had a significant improvement and reached 19.21 g/l and 48.03%, respectively,
compared with those of constant pH operation (14.58 g/l and 36.45%). Fed-batch fermentation with pH-shift control strategy
was also applied to produce propionic acid; the maximal propionic acid yield and glucose conversion efficiency reached 25.23 g/l
and 47.76%, respectively. 相似文献
17.
The transport behavior of five carboxylic acids of relevance in biotechnology (acetic, propionic, lactic, oxalic, citric) in diffusion dialysis and neutralization dialysis through an anion exchange membrane is investigated. The dependence of acid anion flux on base concentration in neutralization dialysis is analyzed in terms of two limiting situations (boundary layer control and membrane control) by an empirical two-parameter flux equation in formal analogy to a Langmuir function. When coupled to a life fermenter, neutralization dialysis is a means to control the pH of the fermentation medium. By removing biotoxic acids, it improves microbial productivity, as exemplified with the Propioni system producing vitamin B 12 and propionic acid. 相似文献
18.
Two biotechnological systems were developed for sucrose conversion into levan and ethanol with Zymomonas mobilis, ensuring a 66.7% transfer of substrate carbon in a batch and 61% carbon transfer in a continuous culture. The effect of
glucose, ethanol, and medium pH on sucrose conversion by Z. mobilis was studied. The addition of ethanol to the fermentation medium, in the final conc. of 100 g/L, uncoupled levan synthesis
from ethanol fermentation. For a continuous culture, the most efficient conversion of substrate carbon into levan was reached
at pH 4.8, giving 64.2 g/L levan, with the levan yield of 0.22 g/g and the productivity of 3.2 g/L/h. 相似文献
19.
The effect of various nitrogen sources on cell growth and lactic acid production was investigated. The most effective nitrogen
source was yeast extract; more yeast extract gave higher cell growth and lactic acid productivity. Yeast extract dosage and
cell growth were proportional up to a yeast extract concentration of 30 g/L, and lactic acid productivity was linearly correlated
up to a yeast extract dosage of 25 g/L. However, increasing the yeast extract content raises the total production cost of
lactic acid. Therefore, we attempted to find the optimum yeast extract dosage for a repeated-batch operation with cell recycling.
The results show that when using Enterococcus faecalis RKY1 only 26% of the yeast extract dosage for a conventional batch fermentation was sufficient to produce the same amount
of lactic acid, whereas the lactic acid concentration in the product stream (92–94 g/L) and lactic acid productivity (6.03–6.20
g/[L·h]) were similar to those of a batch operation. Furthermore, long-term stability was established. 相似文献
20.
Utilizing all forms of sugars derived from lignocellulosic biomass via various pretreatment and hydrolysis process is a primary criterion for selecting a microorganism to produce biofuels and biochemicals. A broad carbon spectra and potential inhibitors such as furan, phenol compounds and weak acids are two major obstacles that limited the application of dilute-acid hydrolysate of lignocellulosics in lactic acid fermentation. Two strains of bacteria isolated from sour cabbage, S3F4 ( Lactobacillus brevis) and XS1T3-4 ( Lactobacillus plantrum), exhibited the ability to utilize various sugars present in dilute-acid hydrolysate of biomass. The S3F4 strain also showed strong resistance to potential fermentation inhibitors such as ferulic acid and furfural. Fermentation in flasks by this strain resulted in 39.1 g/l of lactic acid from dilute acid hydrolysates of corncobs that had initial total sugar concentration of 56.9 g/l (xylose, 46.4 g/l; glucose, 4.0 g/l; arabinose, 6.5 g/l). The hydrolysate of corncobs was readily utilized by S3F4 without detoxification, and the lactic acid concentration obtained in this study was higher compared to other reports. 相似文献
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