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1.
Rotary biofilm contactor (RBC) is a reactor consisting of plastic discs that act as supports for micro-organisms. The discs are mounted on a horizontal shaft and placed in a medium-containing vessel. During nitrogen-rich growth phase, mycelia ofRhizopus oryzae ATCC 20344 grew on and around the discs and formed the “biofilm” of self-immobilized cells on the surface of the plastic discs. During the fermentation phase, the discs are slowly rotated, and the biofilms are exposed to the medium and the air space, alternately. With RBC, in the presence of CaCO3,Rhizopus biofilm consumes glucose and produces fumaric acid with a volumetric productivity of 3.78 g/L/h within 24 h. The volumetric productivity is about threefolds higher with RBC than with a stirred-tank fermenter with CaCO3. Furthermore, the duration of fermentation is one-third of the stirred-tank system. The immobilized biofilm is active for over a 2-wk period with repetitive use without loss of activity. 相似文献
2.
Lactic acid is used as a food additive for flavor and preservation and a precursor in the development of poly-lactic acid,
a product used to make biodegradable plastics and textiles. Rhizopus oryzae NRRL 395 is known to be a strain that produces optically pure l-(+)-lactic acid. The morphology of Rhizopus cultures is complex, forming filamentous, clumps, and pellet mycelia. Different morphology growth has significant effects
on lactic acid production. In bioreactors, the filamentous or clump mycelia increase the viscosity of the medium, wrap around
impellers, and block the nutrient transportation, leading to a decrease in production efficiency and bioreactor performance.
Growing fungi in pellet form can significantly improve these problems. In this study, factors that affect lactic acid production
in pelletized flask cultures using R. oryzae NRRL 395 were investigated in detail. Completely randomized designs were used to determine the influence of culture temperature,
time, concentration of glucose, and inoculum size. Lactic acid fermentation using clump and pellet morphologies were performed
in a 5 L fermentor at the optimal values obtained from flask culture. Finally, fed-batch culture was used to enhance the lactate
concentration in broth. The final lactate concentration of fed-batch culture reached 92 g/L. The data presented in the article
can provide useful information on optimizing lactic acid production using alternative source materials. 相似文献
3.
The effect of an external supply of carbon dioxide and pH on the production of succinic acid by Anaerobiospirillum succiniciproducens was studied. In a rich medium containing yeast extract and peptone, when the external carbon dioxide supply was provided
by a 1.5M Na 2CO 3 solution that also was used to maintain the pH at 6.0, no additional carbon dioxide supply was needed. In fact, sparging
CO 2 gas into the fermenter at 0.025 L/L-min or higher rates resulted in significant decreases in both production rate and yield
of succinate. Under the same conditions, the production of the main by-product acetate was not affected by sparging CO 2 gas into the fermenter. The optimum pH (pH 6.0) for the production of succinic acid was found to be in agreement with results
previously reported in the literature. Succinic acid production also was studied in an industrial-type inexpensive medium
in which light steep water was the only source of organic nutrients. At pH 6.0 and with a CO 2 gas sparge rate of 0.08 L/L-min, succinate concentration reached a maximum of 32 g/L in 27 h with a yield of 0.99 g succinate/g
glucose consumed. 相似文献
4.
The genus Propionibacterium acidipropionici was grown under pH-controlled batch fermentation conditions for the production of acetic and propionic acids using 19.1 g/L glucose as a carbon source. The optimum pH range was found to be between 5.5 and 6.5. Bacterial metabolism and fermentation pathways were altered at pH values outside this range. Lactic acid was produced as a key intermediate, with the final acetic and propionic acid production entirely dependent on the cell's ability to metabolize the lactic acid. Most of the glucose in the medium was consumed in less than 20 h of fermentation and converted to lactic acid. Batch fermentation at pH 6 showed that lactic acid was completely utilized to produce 8.5 g/L propionic acid and 5.7 g/L acetic acid. However, the bacteria were unable to metabolize lactic acid at pH 7, resulting in 0.7 g/L propionic acid and 7.0 g/L acetic acid in the fermenter. A kinetic study of batch fermentation at pH 6 showed two distinct growth phases during the fermentation. Most of the cell growth was achieved in the exponential growth stage when glucose was consumed as a main substrate. A nonexponential growth stage was observed when lactic acid was utilized as a carbon source, producing propionic and acetic acids as secondary metabolites. 相似文献
5.
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
6.
This work represents a continuation of our investigation into environmental conditions that promote lactic acid synthesis
by Zymomonas mobilis. The characteristic near theoretical yield of ethanol from glucose by Z. mobilis can be compromised by the synthesis of d- and l-lactic acid. The production of lactic acid is exacerbated by the following conditions: pH 6.0, yeast extract, and reduced
growth rate. At a specific growth rate of 0.048/h, the average yield of dl-lactate from glucose in a yeast extract-based medium at pH 6.0 was 0.15 g/g. This represents a reduction in ethanol yield
of about 10% relative to the yield at a growth rate of 0.15/h. Very little lactic acid was produced at pH 5.0 or using a defined
salts medium (without yeast extract) Under permissive and comparable culture conditions, a tetracycline-resistant, d- ldh negative mutant produced about 50% less lactic acid than its parent strain Zm ATCC 39676. d-lactic acid was detected in the cell-free spent fermentation medium of the mutant, but this could be owing to the presence
of a racemase enzyme. Under the steady-state growth conditions provided by the chemostat, the specific rate of glucose consumption
was altered at a constant growth rate of 0.075/h. Shifting from glucose-limited to nitrogen-limited growth, or increasing
the temperature, caused an increase in the specific rate of glucose catabolism. There was good correlation between an increase
in glycolytic flux and a decrease in lactic acid yield from glucose. This study points to a mechanistic link between the glycolytic
flux and the control of end-product glucose metabolism. Implications of reduced glycolytic flux in pentose-fermenting recombinant
Z. mobilis strains, relative to increased byproduct synthesis, is discussed. 相似文献
7.
Optimization of submerged culture conditions for the production of mycelial growth and exopolysaccharides (EPSs) by Collybia maculata was investigated. The optimum temperature and the initial pH for EPS production in a shake-flask culture of C. maculata were found to be 20°C and 5.5, respectively. Among the various medium’s constituents examined, glucose, Martone A-1, K 2HPO 4, and CaCl 2 were the most suitable carbon, nitrogen, and mineral sources for EPS production, respectively. The optimum concentration
of the medium’s ingredients determined using the orthogonal matrix method was as follows: 30 g/L of glucose, 20 g/L of Martone
A-1, 1g/L of K 2HPO 4, and 1g/L of CaCl 2. Under the optimized culture conditions, the maximum concentration of EPSs in a 5-L stirred-tank reactor was 2.4 g/L, which
was approximately five times higher than that in the basal medium. A comparative fermentation result showed that the EPS productivity
in an airlift reactor was higher than that in the stirred-tank reactor despite the lower mycelial growth rate. The specific
productivities and the yield coefficients in the airlift reactor were higher than those in the stirred-tank reactor even though
the volumetric productivities were higher in the stirred-tank reactor than in the airlift reactor. 相似文献
8.
The effect of nutrients on L(+)-lactic acid production from glucose was investigated using Rhizopus oryzae ATCC 523 11. From the shake-flask experiments, the optimal medium composition was defined for improved lactic-acid production.
In order to enhance lactic-acid production rate and product yield, controlled aeration in a bubble column was conducted under
optimal conditions. Results showed a maximum lactic-acid production rate of 2.58 g/L/h was obtained with an initial glucose
concentration of 94 g/L. Finallactic-acid concentration of 83 g/L was achieved after 32 h of fermentation with a weight of
0.88 glactic acid/g glucose consumed. 相似文献
9.
In submerged culture of Ganoderma lucidum, the pH optimum for cell growth has been shown to be lower than that for exopolysaccharides (EPS) formation. Therefore, in
the present study, a two-stage pH-control strategy was employed to maximize the productions of mycelial biomass and EPS. When
compared, a batch culture without pH control had a maximum concentration of EPS and endopolysaccharides, which was much lower
than those with pH control. Maximum mycelial growth (12.5 g/L) and EPS production (4.7 g/L) were achieved by shifting the
controlled pH from 3.0 to 6.0 after day 4. The contrast between the controlled-pH process and uncontrolled pH was marked.
By using various two-stage culture processes, it was also observed that culture pH has a significant affect on the yield of
product, mycelial morphology, chemical composition, and molecular weight of EPS. A detailed observation of mycelial morphology
revealed that the productive morphological form for EPS production was a dispersed pellet (controlled pH shifting from 3.0
to 6.0) rather than a compact pellet with a dense core area (controlled pH 4.5) or a feather-like pellet (controlled pH shifting
from 6.0 to 3.0). Three different polysaccharides were obtained from each pH conditions, and their molecular weights and chemical
compositions were significantly different. 相似文献
10.
The production of L(+)-lactic acid using alginate immobilized Rhizopus oryzae in tapered-column fluidized-bed batch reactor was tested and simulated using the kinetic data taken independently in shake-flask cultures. The data show saturation kinetics with substrate and product inhibitions in linear form. Analysis of the kinetic data gave kinetic constants: V m, 11.04 g lactic acid/(L-bead. h); K m, 20.9 g glucose/L; and K i, 365 g glucose/L for lactic acid production. The product inhibition constant, K p, was found to be 316 g lactic acid/L. The simulation results showed a good agreement with the experimental results when the initial lag phase was taken into account in the simulation model. Without the adjustment for the initial lag period, the kinetic model showed higher conversion. Starting with a glucose concentration of 150 g/L, it was possible to produce 73 g/L of L(+)-lactic acid in 44.5 h. The lactic acid yield was 64.8% by weight based on the amount of glucose consumed. 相似文献
11.
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 of Candida 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
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.
Growth and lactic acid production of Lactobacillus delbreuckii were compared using glucose and lactose as carbon sources. A continuous-flow stirred-tank fermenter was coupled with a cross-flow
filtration unit to permit operation at high-cell concentrations. At steady state, yeast extract requirements for lactic-acid
production were lower when glucose was used as a substrate than with lactose fermentation. Once steady state was obtained,
with glucose feed, it was possible to lower the yeast extract concentration without affecting biomass concentration and lactic
acid production. The lacticacid concentration that inhibited cell growth and lactic acid production was found to depend on
the choice of a carbon substrate. 相似文献
14.
Actinobacillus succinogenes 130 Z was used to produce succinic acid from cheese whey in this study. At the presence of external CO 2 supply, the effects of initial cheese whey concentration, pH, and inoculum size on the succinic acid production were studied.
The by-product formation during the fermentation process was also analyzed. The highest succinic acid yield of 0.57 was obtained
at initial cheese whey concentration of 50 g/L, while the highest succinic acid productivity of 0.58 g h −1 L −1 was obtained at initial cheese whey concentration of 100 g/L. Increase in pH and inoculum size caused higher succinic acid
yield and productivity. At the preferred fermentation condition of pH 6.8, inoculum size of 5% and initial cheese whey concentration
of 50 g/L, succinic acid yield of 0.57, and productivity of 0.44 g h −1 L −1 were obtained. Acetic acid and formic acid were the main by-products throughout the fermentation run of 48 h. It is feasible
to produce succinic acid using lactose from cheese whey as carbon resource by A. succinogenes 130 Z. 相似文献
15.
The fermentation characteristics of a recombinant strain of Zymomonas mobilis ZM4(pZB5) capable of converting both glucose and xylose to ethanol have been further investigated. Previous studies have
shown that the strain ZM4(pZB5) was capable of converting a mixture o 65 g/L of glucose and 65 g/L of xylose to 62 g/L of
ethanol in 48 h with an overall yield of 0.46 g/g. Higher sugar concentrations (e.g., 75/75 g/L) resulted in incomplete xylose
utilization (80 h). In the present study, further kinetic evaluations at high sugar levels are reported. Acetate inhibition
studies and evaluation of temperature and pH effects indicated increased maximum specific uptake rates of glucose and xylose
under stressed conditions with increased metabolic uncoupling. A high-productivity system was developed that involved a membrane
bioreactor with cell recycling. At sugar concentrations of approx 50/50 g/L of glucose/xylose, an ethanol concentration of
50 g/L, an ethanol productivity of approx 5 g/(L·h), and a yield ( Y
p/s) of 0.50 g/g were achieved. Decreases in cell viability were found in this system after attainment of an initial steady state
(40–60 h); a slow bleed of concentrated cells may be required to overcome this problem. 相似文献
16.
This study examined the continuous cofermentation performance characteristics of a dilute-acid “prehydrolysate-adapted” recombinant
Zymomonas 39676:pZB4L and builds on the pH-stat batch fermentations with this recombinant that we reported on last year. Substitution
of yeast extract by 1% (w/v) corn steep liquor (CSL) (50% solids) and Mg (2 mM) did not alter the coferm entation performance.
Using declared assumptions, the cost of using CSL and Mg was estimated to be 12.5c/gal of ethanol with a possibility of 50%
cost reduction using fourfold less CSL with 0.1% diammonium phosphate. Because of competition for a common sugar transporter
that exhibits a higher affinity for glucose, utilization of glucose was complete whereas xylose was always present in the
chemostat effluent. The ethanol yield, based on sugar used, was 94% of theoretical maximum. Altering the sugar ratio of the
synthetic dilute acid hardwood prehydrolysate did not appear to significantly change the pattern of xylose utilization. Using
a criterion of 80% sugar utilization for determining the maximum dilution rate ( D
max), changing the composition of the feed from 4% xylose to 3%, and simultaneously increasing the glucose from 0.8 to 1.8% shifted
D
max from 0.07 to 0.08/h. With equal amounts of both sugars (2.5%), D
max was 0.07/h. By comparison to a similar investigation with rec Zm CP4:pZB5 with a 4% equal mixture of xylose and glucose,
we observed that at pH 5.0, the D
max was 0.064/h and shifted to 0.084/h at pH 5.75. At a level of 0.4% (w/v) acetic acid in the CSL-based medium with 3% xylose
and 1.8% glucose at pH 5.75, the D
max for the adapted recombinant shifted from 0.08 to 0.048/h, and the corresponding maximum volumetric ethanol productivity decreased
45%, from 1.52 to 0.84 g/(L·h). Under these conditions of continuous culture, linear regression of a Pirt plot of the specific
rate of sugar utilization vs D showed that 4 g/L of acetic acid did not affect the maximum growth yield (0.030 g dry cell mass/g sugar), but did increase
the maintenance coefficient twofold, from 0.46 to 1.0 g of sugar/(g of cell·h). 相似文献
17.
Conversion of food wastes into lactic acid by simultaneous saccharification and fermentation (SSF) was investigated. The process
involves saccharification of the starch component in food wastes by a commercial amylolytic enzyme preparation (a mixture
of amyloglucosidase, α-amylase, and protease) and fermentation by Lactobacillus delbrueckii. The highest observed overall yield of lactic acid in the SSF was 91% of theoretical. Lactic acid concentration as high as
80 g/L was attainable in 48 h of the SSF. The optimum operating conditions for the maximum productivity were found to be 42°C
and pH 6.0. Without supplementation of nitrogen-containing nutrients, the lactic acid yield in the SSF decreased to 60%: 27
g/L of lactic acid from 60 g/L of food waste. The overall performance of the SSF, however, was not significantly affected
by the elimination of mineral supplements. 相似文献
18.
Pleurotus ostreatus mushroom mycelium was cultivated in submerged culture in shake-flask experiments with acid extract from peat and yeast extract
as nutrient sources. Different concentrations of water-diluted peat extract were tested in an attempt to overcome the effect
of growth inhibitors apparently present in nondiluted peat extracts. The best results were obtained with a ratio of one part
of peat extract diluted with one part of water. Several operating variables were studied to optimize the growth of mycelial
biomass of P. ostreatus. The best results produced approximately 5 g/L dry biomass with a yield of 60% and an efficiency of 33%. These results were
obtained in 8 d at 5% (v/v) inoculum ratio, 28°C, pH of 5.0, and 150 rpm. 相似文献
19.
Factors in a cultivation medium affecting fungal growth morphology and funmaric acid production by Rhizopus oryzae ATCC 20344 were investigated. These factors included the initial pH value and trace metals such as zinc, magnesium, iron,
and manganese in the cultivation medium. It was found that a significant change in the growth morphology of R. oryzae ATCC 20344 occurs when the initial pH value is varied. A lower initial pH value in the cultivation medium was inhibitory
to fungal growth, and fast growth in the cultivation medium at a higher initial pH value promoted, the formation of large
pellets or filamentous forms. Trace metals in the cultivation media also had significant effects on pellet formation and fumaric
acid fermentation. 相似文献
20.
Cultivations of filamentous fungi in stirred tank reactors (STRs) to produce metabolites are often limited by insufficient mixing and mass transfer because of the formation of mycelial clumps inside the reactors. This study developed an acid-adapted preculture approach to control the morphology of filamentous Rhizopus arrhizus in a STR, consequently to enhance the production yield and productivity of L(+)-lactic acid efficiently using waste potato starch as substrate. Using the acid-adapted precultures as inoculum, the morphology of R. arrhizus was maintained as large clumps, coalesced loose small pellets, and freely dispersed small pellets. The highest lactic acid concentration of 85.7 g/L with a yield of 86% was obtained in association with the formation of coalesced loose small pellets. The results indicate that the use of the acid-adapted precultures as inoculum is a promising approach for lactic acid production in STRs. 相似文献
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