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1.
Agro-stovers are the most abundant substrates for producing lactic acid, which has great potential application in the production of biodegradable and biocompatible polylactic acid polymers. However, chemical pretreatments on agro-stovers generate inhibitors that repress the subsequent lactic acid fermentation. In this study, three bacterial strains (Enterococcus faecalis B101, Acinetobacter calcoaceticus C1, and Pseudomonas aeruginosa CS) isolated from dye-polluted soils could utilize phenolic inhibitor mimics (vanillin, 4- hydroxybenzaldehyde, or syringaldehyde) from alkaline pretreated corn stovers as a sole carbon source. Lactic acid titer increased from 27.42 g/L (Bacillus coagulans LA204 alone) to 44.76 g/L (CS and LA204) using 50 g/L glucose with 1 g/L 4-hydroxybenzaldehyde added. Lactic acid production from 50 g/L ammonia pretreated corn stover was increased nearly twofold by inoculating phenolic degradation bacteria and lactic acid bacteria (C1& Lactobacillus pentosus FL0421). In the control (FL0421 alone), only 16.98 g/L of lactic acid was produced. The isolated and identified strains degraded the phenolic compounds and increased the lactic acid production from glucose and ammonia pretreated corn stover. These characteristics of the strains support industrial application with efficient in situ detoxification of phenolic compounds during lactic acid production from agro-stovers using simultaneous saccharification and fermentation (SSF). 相似文献
2.
Aqueous-ammonia-steeped switchgrass was subject to simultaneous saccharification and fermentation (SSF) in two pilot-scale
bioreactors (50- and 350-L working volume). Switchgrass was pretreated by soaking in ammonium hydroxide (30%) with solid to
liquid ratio of 5 L ammonium hydroxide per kilogram dry switchgrass for 5 days in 75-L steeping vessels without agitation
at ambient temperatures (15 to 33 °C). SSF of the pretreated biomass was carried out using Saccharomyces cerevisiae (D 5A) at approximately 2% glucan and 77 filter paper units per gram cellulose enzyme loading (Spezyme CP). The 50-L fermentation
was carried out aseptically, whereas the 350-L fermentation was semiaseptic. The percentage of maximum theoretical ethanol
yields achieved was 73% in the 50-L reactor and 52–74% in the 350-L reactor due to the difference in asepsis. The 350-L fermentation
was contaminated by acid-producing bacteria (lactic and acetic acid concentrations approaching 10 g/L), and this resulted
in lower ethanol production. Despite this problem, the pilot-scale SSF of aqueous-ammonia-pretreated switchgrass has shown
promising results similar to laboratory-scale experiments. This work demonstrates challenges in pilot-scale fermentations
with material handling, aseptic conditions, and bacterial contamination for cellulosic fermentations to biofuels. 相似文献
3.
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
4.
The production of nisin, a natural food preservative, by Lactococcus lactis subsp. lactis (ATCC 11454) is associated with the simultaneous formation of lactic acid during fermentation in a whey-based medium. As
a result of the low concentration and high separation cost of lactic acid, recovering lactic acid as a product may not be
economical, but its removal from the fermentation broth is important because the accumulation of lactic acid inhibits nisin
biosynthesis. In this study, lactic acid removal was accomplished by biological means. A mixed culture of L. lactis and Saccharomyces cerevisiae was established in order to stimulate the production of nisin via the in situ consumption of lactic acid by the yeast strain, which is capable of utilizing lactic acid as carbon source. The S. cerevisiae in the mixed culture did not compete with the nisin-producing bacteria because the yeast does not utilize lactose, the major
carbohydrate in whey for bacterial growth and nisin production. The results showed that lactic acid produced by the bacteria
was almost totally utilized by the yeast and the pH of the mixed culture could be maintained at around 6.0. Nisin production
by the mixed culture system reached 150.3 mg/L, which was 0.85 times higher than that by a pure culture of L. lactis. 相似文献
5.
Current research indicates the ethanol fuel production from lignocellulosic materials, such as residual wood chips from the
cellulose industry, as new emerging technology. This work aimed at evaluating the ethanol production from hemicellulose of
eucalyptus chips by diluted acid pretreatment and the subsequent fermentation of the generated hydrolysate by a flocculating
strain of Pichia stipitis. The remaining solid fraction generated after pretreatment was subjected to enzymatic hydrolysis, which was carried out simultaneously
with glucose fermentation [saccharification and fermentation (SSF) process] using a strain of Saccharomyces cerevisiae. The acid pretreatment was evaluated using a central composite design for sulfuric acid concentration (1.0–4.0 v/ v) and solid to liquid ratio (1:2–1:4, grams to milliliter) as independent variables. A maximum xylose concentration of 50 g/L
was obtained in the hemicellulosic hydrolysate. The fermentation of hemicellulosic hydrolysate and the SSF process were performed
in bioreactors and the final ethanol concentrations of 15.3 g/L and 28.7 g/L were obtained, respectively. 相似文献
6.
Using the simultaneoussaccharification and fermentation (SSF) technique, pulp mill solid waste cellulose was converted into
glucose using cellulase enzyme and glucose into lacticacid using NRRL B445. SSF experiments were conducted at various pH levels,
temperatures, and nutrient concentrations, and the lactic acid yield ranged from 86 to 97%. The depletion of xylose in SSF
was further investigated by inoculating NRRL B445 into a xylose-only medium. On prolonged incubation, depletion of xylose
with lactic acid production was observed. An experimental procedure with a nonglucose medium was developed to eliminate the
lag phase. From xylose fermentation, Lactobacillus delbrueckii yielded 88–92% lactic acid and 2–12% acetic acid. 相似文献
7.
Substrate concentration in lactic acid fermentation broth could not be controlled well by traditional feeding methods, including
constant, intermittent, and exponential feeding methods, in fed-batch experiments. A simple feedback feeding method based
on pH was proposed to control pH and substrate concentration synchronously to enhance lactic acid production in fed-batch
culture. As the linear relationship between the consumption amounts of alkali and that of substrate was concluded during lactic
acid fermentation, the alkali and substrate in the feeding broth were mixed together proportionally. Thus, the concentration
of substrate could be controlled through the adjustment of pH automatically. In the fed-batch lactic acid fermentation with
Lactobacillus lactis-11 by this method, the residual glucose concentration in fermentation broth was controlled between 4.1 and 4.9 g L −1, and the highest concentration of lactic acid, maximum cell dry weight, volumetric productivity of lactic acid, and yield
were 96.3 g L −1, 4.7 g L −1, 1.9 g L −1 h −1, and 0.99 g lactic acid per gram of glucose, respectively, compared to 82.7 g L −1, 3.31 g L −1, 1.7 g L −1 h −1, and 0.92 g lactic acid per gram of glucose in batch culture. This feeding method was simple and easily operated and could
be feasible for industrial lactic acid production in the future. 相似文献
8.
Citric acid (CA) production has been conducted through a careful strain selection, physical–chemical optimization and mutation.
The aim of this work was to optimize the physical–chemical conditions of CA production by solid-state fermentation (SSF) using
the Aspergillus niger LPB BC strain, which was isolated in our laboratory. The parental and mutant strain showed a good production of CA using
citric pulp (CP) as a substrate. The physical–chemical parameters were optimized and the best production was reached at 65%
moisture, 30 °C and pH 5.5. The influence of the addition of commercial and alternative sugars, nitrogen sources, salts, and
alcohols was also studied. The best results (445.4 g of CA/kg of CP) were obtained with sugarcane molasses and 4% methanol
( v/ w). The mutagenesis induction of LPB BC was performed with UV irradiation. Eleven mutant strains were tested in SSF where two
mutants showed a higher CA production when compared to the parental strain. A. niger LPB B3 produced 537.6 g of CA/kg of CP on the sixth day of fermentation, while A. niger LPB B6 produced 616.5 g of CA/kg of CP on the fourth day of fermentation, representing a 19.5% and 37% gain, respectively. 相似文献
9.
In this study, a fermentor consisting of four linked stirred towers that can be used for simultaneous saccharification and
fermentation (SSF) and for the accumulation of cell mass was applied to the continuous production of ethanol using cassava
as the starchy material. For the continuous process with SSF, the pretreated cassava liquor and saccharification enzyme at
total sugar concentrations of 175 g/L and 195 g/L were continuously fed to the fermentor with dilution rates of 0.014, 0.021,
0.031, 0.042, and 0.05 h −1. Considering the maximum saccharification time, the highest volumetric productivity and ethanol yield were observed at a
dilution rate of 0.042 h −1. At dilution rates in the range of 0.014 h −1 to 0.042 h −1, high production rates were observed, and the yeast in the first to fourth fermentor showed long-term stability for 2 months
with good performance. Under the optimal culture conditions with a feed sugar concentration of 195 g/L and dilution rate of
0.042 h −1, the ethanol volumetric productivity and ethanol yield were 3.58 g/L∙h and 86.2%, respectively. The cell concentrations in
the first to fourth stirred tower fermentors were 74.3, 71.5, 71.2, and 70.1 g dry cell/L, respectively. The self-flocculating
yeast, Saccharomyces cerevisiae CHFY0321, developed by our group showed excellent fermentation results under continuous ethanol production. 相似文献
10.
Ethanol production was studied in simultaneous saccharification and fermentation (SSF) of steam-pretreated spruce at 42°C,
using a thermotolerant yeast. Three yeast strains of Kluyveromyces marxianus were compared in test fermentations. SSF experiments were performed with the best of these on 5% (w/w) of substrate at a
cellulase loading of 37 filter paper units/g of cellulose, and a β-glucosidase loading of 38 IU/gof cellulose. The detoxification
of the substrate and the lack of pH control in the experiments increased the final ethanol concentration. The final ethanol
yield was 15% lower compared to SSF with Saccharomyces cerevisiae at 37°C, owing to the cessation of ethanol fermentation after the first 10 h. 相似文献
11.
In order to construct a strain that converts sugar mixture and resist/metabolize inhibitors in lignocellulosic dilute-acid
hydrolysate, the biotechnology of inactive intergeneric fusion between Saccharomyces cerevisiae and Pachysolen tannophilis was performed. Fusant 1 was successfully obtained as a hybrid strain, which was screened out by xylose and mixed sugar (xylose
and glucose) fermentation. This strain showed good abilities of ethanol production, ethanol tolerance, and resistance to the
toxic inhibitors presenting in the hydrolysate. The maximum volumetric yield of ethanol and yield of xylitol in mixed sugar
was 9.52 g/l and 0.44 g/g, respectively. The results indicated that the constructed strain Fusant 1 was a good producer for
ethanol and xylitol from lignocellulosic dilute-acid hydrolysate.
F. Yan, F. Bai, and S. Tian contributed equally to this research work. 相似文献
12.
This study evaluated the production of lignocellulose-degrading enzymes by solid-state fermentation (SSF) using a microbial consortium of Aspergillus fumigatus SCBM6 and A. niger SCBM1 (AFN extract). The fungal strains were cultivated in sugarcane bagasse (SCB) and wheat bran (WB) as lignocellulosic substrates for 7 days at 30 °C. After SSF, the highest peaks of enzyme production were 150 and 80 U g−1 for β-xylosidase and β-glucosidase at 48 h, 375 U g−1 for xylanase at 96 h, and 80 U g−1 for endoglucanase and 4 U g−1 for cellulase activity on filter paper (FPase) at 144 h. The efficiency of the produced AFN extract was investigated in the enzymatic hydrolysis of crude biomass sorghum (BS) and after the removal of extractives (ES). After saccharification, the glucose and xylose concentrations were 10× superior in ES than in BS hydrolysate (2.5 g L−1 after 12 h). The presence of inhibitors of alcoholic fermentation, such as formic acid, was also reduced in ES hydrolysates, indicating that the removal of extractives positively contributed to the effectiveness of enzymatic hydrolysis of biomass sorghum using AFN extract. 相似文献
13.
Soluble coffee, being one of the world’s most popular consuming drinks, produces a considerable amount of spent coffee ground (SCG) along with its production. The SCG could function as a potential lignocellulosic feedstock for production of bioproducts. The objective of this study is to investigate the possible optimal condition of dilute acid hydrolysis (DAH) at high solids and mild temperature condition to release the reducing sugars from SCG. The optimal condition was found to be 5.3 % ( w/ w) sulfuric acid concentration and 118 min reaction time. Under the optimal condition, the mean yield of reducing sugars from enzymatic saccharification of defatted SCG acid hydrolysate was 563 mg/g. The SCG hydrolysate was then successfully applied to culture Lipomyces starkeyi for microbial oil fermentation without showing any inhibition. The results suggested that dilute acid hydrolysis followed by enzymatic saccharification has the great potential to convert SCG carbohydrates to reducing sugars. This study is useful for the further developing of biorefinery using SCG as feedstock at a large scale. 相似文献
14.
The conversion of low-priced glycerol to higher value products has been proposed as a way to improve the economic viability
of the biofuels industry. In a previous study, the conversion of glycerol to ethanol in a metabolically engineered strain
of Saccharomyces cerevisiae was accomplished by minimizing the synthesis of glycerol, the main by-product in ethanol fermentation processing. To further
improve ethanol production, overexpression of the native genes involved in conversion of pyruvate to ethanol in S. cerevisiae was successfully accomplished. The overexpression of an alcohol dehydrogenase ( adh1) and a pyruvate decarboxylase ( pdc1) caused an increase in growth rate and glycerol consumption under fermentative conditions, which led to a slight increase
of the final ethanol yield. The overall expression of the adh1 and pdc1 genes in the modified strains, combined with the lack of the fps1 and gpd2 genes, resulted in a 1.4-fold increase (about 5.4 g/L ethanol produced) in fps1Δgpd2Δ (p GcyaDak, p GupCas) (about 4.0 g/L ethanol produced). In summary, it is possible to improve the ethanol yield by overexpression of the genes
involved in the conversion of pyruvate to ethanol in engineered S. cerevisiae using glycerol as substrate. 相似文献
15.
The conversion of biomass into ethanol using fast, cheap, and efficient methodologies to disintegrate and hydrolyse the lignocellulosic
biomass is the major challenge of the production of the second-generation ethanol. This revision describes the most relevant
advances on the conversion process of lignocellulose materials into ethanol, development of new xylose-fermenting strains
of Saccharomyces cerevisiae using classical and modern genetic tools and strategies, elucidation of the expression of some complex industrial phenotypes,
tolerance mechanisms of S. cerevisiae to lignocellulosic inhibitors, monitoring and strategies to improve fermentation processes. In the last decade, numerous
engineered pentose-fermenting yeasts have been developed using molecular biology tools. The increase in the tolerance of S. cerevisiae to inhibitors is still an important issue to be exploited. As the industrial systems of ethanol production operate under
non-sterile conditions, microbial subpopulations are generated, depending on the operational conditions and the levels of
contaminants. Among the most critical requirements for production of the second-generation ethanol is the reduction in the
levels of toxic by-products of the lignocellulosic hydrolysates and the production of low-cost and efficient cellulosic enzymes.
A number of procedures have been established for the conversion of lignocellulosic materials into ethanol, but none of them
are completely satisfactory when process time, costs, and efficiency are considered. 相似文献
16.
Experimental results are presented for continuous conversion of pretreated hardwood flour to ethanol. A simultaneous saccharification
and fermentation (SSF) system comprised of Trichoderma reesei cellulase supplemented with additional β-glucosidase and fermentation by Saccharomyces cerevisiae was used for most experiments, with data also presented for a direct microbial conversion (DMC) system comprised of Clostridium thermocellum. Using a batch SSF system, dilute acid pretreatment of mixed hardwood at short residence time(10 s, 220°C, 1% H 2SO 4) was compared to poplar wood pretreated at longer residence time (20 min, 160°C, 0.45% H 2SO 4). 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
17.
Previous shake flask and stirred tank evaluations of temperature tolerant (37–43°C) yeasts in simultaneous saccharification and fermentation (SSF) on Sigmacell-50 cellulose substrates to ethanol have identified several good microorganisms for further SSF studies (27). Of these, the glucose fermenting yeastCandida acidothermophilum, C. brassicae, Saccharomyces cerevisiae, S. uvarum, and a mixed culture of the cellobiose fermenting yeastBrettanomyces clausenii withS. cerevisiae as a control were chosen for shake flask SSF screening experiments with pretreated wheat straw. This study indicates that theSaccharomyces strainscerevisiae anduvarum, give very good performance at high cellulase loadings or when supplemented with Novo-188 β-glucosidase. In fact, with the higher enzyme loadings these yeast will give complete conversion of cellulose to ethanol. Yet at the lower, more economical enzyme loadings, the mixed culture ofBrettanomyces clausenii andS. cerevisiae performs better than any single yeast. 相似文献
18.
Lactic acid (LA) is an important organic acid with broad industrial applications. Considered as an environmentally friendly alternative to petroleum-based plastic with a wide range of applications, polylactic acid has generated a great deal of interest and therefore the demand for optically pure l- or d-lactic acid has increased accordingly. Microbial fermentation is the industrial route for LA production. LA bacteria and certain genetic engineering bacteria are widely used for LA production. Although some fungi, such as Saccharomyces cerevisiae, are not natural LA producers, they have recently received increased attention for LA production because of their acid tolerance. The main challenge for LA bioproduction is the high cost of substrates. The development of LA production from cost-effective biomasses is a potential solution to reduce the cost of LA production. This review examined and discussed recent progress in optically pure l-lactic acid and optically pure d-lactic acid fermentation. The utilization of inexpensive substrates is also focused on. Additionally, for PLA production, a complete biological process by one-step fermentation from renewable resources is also currently being developed by metabolically engineered bacteria. We also summarize the strategies and procedures for metabolically engineering microorganisms producing PLA. In addition, there exists some challenges to efficiently produce PLA, therefore strategies to overcome these challenges through metabolic engineering combined with enzyme engineering are also discussed. 相似文献
19.
Four promising woody crops (Populus maximowiczii x nigra (NE388), P. trichocarpa x deltoides (Nll), P. tremuloides, and Sweetgum Liquidambar styraciflua) were pretreated by dilute sulfuric acid and evaluated in the simultaneous saccharification and fermentation (SSF) process
for ethanol production. The yeast Saccharomyces cerevisiae was used in the fermentations alone, and in mixed cultures with β -glucosidase producing Brettanomyces dausenii. Commercial Genencor 150L cellulase enyme was either employed alone or supplemented with β - glucosidase. All SSFs were run at 37 …C for 8 d and compared to saccharifications at 45…C under the same enzyme loadings. S. cerevisiae alone achieved the highest ethanol yields and rates of hydrolysis at the higher enzyme loadings, whereas the mixed culture
performed better at the lower enzyme loadings without β -glucosidase supplementation. The best overall rates of fermentation
(3 d) and final theoretical ethanol yields (86–90%) were achieved with P. maximowiczii x nigra (NE388) and Sweetgum Liquidambar styraciflua, followed by P. tremuloides and P. trichocarpa x deltoides (N1l) with slightly slower rates and lower yields. Although there were some differences in SSF performance, all these pretreated
woody crops show promise as substrates for ethanol production. 相似文献
20.
In this paper, four nonionic surfactants with different hydrophilic–lipophilic balance (HLB) based on sorbitan monolaurate
were synthesized by introducing ethylene oxide gas ( n = 20, 40, 60, and 80 ethylene oxide units). The chemical structure of the prepared ethoxylated surfactants was confirmed
using Fourier transform-infrared and 1H NMR spectroscopes. The surface tension and thermodynamic properties of the prepared surfactants have been studied. The simultaneous
saccharification and fermentation (SSF) process for ethanol production from microwave/alkali pretreated wheat straw has been
assayed using nonionic surfactants have different ethylene oxide units. Ethanol yield was 82% and 61% for Kluyveromyces marxianus and Saccharomyces cerevisiae, respectively, with the addition of 2.5 g/l of the prepared nonionic surfactant (HLB = 18.2). Results show that the production
of ethanol from microwave/alkali pretreated wheat straw increased with increasing the (HLB) value of the nonionic surfactant. 相似文献
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