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Abstract Methods for obtaining high-concentration (ca. 40 g/L) ethanol from cassava stem (CS) were explored by investigating the effects of acid hydrolysis conditions, hydrolysate concentration, and intermittent inoculation of yeast on ethanol fermentation. Two-step acid hydrolysis demonstrated that a reduction in autoclaving temperature from 121 °C to 111 °C remarkably lowered the furfural concentration in the hydrolysate, with only ±10% differences in the glucose and xylose concentrations. For the concentration of sugars in the CS hydrolysate, the acid hydrolysate prepared with CS concentration of 200 g/L was used instead of distilled water for the second step of acid hydrolysis using new CS biomass (i.e., two-times acid hydrolysis). This produced a concentrated hydrolysate containing 95 g/L of glucose and 0.95 g/L furfural. Saccharomyces cerevisiae strain IAM 4178 was inoculated into the concentrated CS hydrolysate after verifying its furfural tolerance. Furfural was rapidly degraded and glucose was converted to ethanol during the startup period, whereas cell density decreased to approximately 10% of the initial value and ethanol production ceased by 72 h. IAM 4178 was then re-inoculated intermittently to maintain the cell density at 108 cells/mL, which eventually resulted in the complete uptake of glucose and the production of high concentrations of ethanol, up to 37.5 g/L. Highlights • Two-time acid hydrolysis of cassava stem to produce high-concentration bioethanol. • Reduction of furfural in the hydrolysate by lowering the autoclaving temperature. • Concentration of glucose in the hydrolysate by two-time acid hydrolysis. • Maintenance of yeast cell density by intermittent yeast inoculation. • Complete uptake of glucose and production of 37.5 g/L of ethanol. [ABSTRACT FROM AUTHOR]

Cassava starch is an abundant feedstock for biological transformation to ethanol, however, its industrial processing needs further improvements to enhance efficiency and cost-effectiveness. In the present study, a low-cost catalyst (CC-SO3H) was synthesized by partial carbonization and sulfonation of crystalline cellulose, which was thermally stable and reactive at 160 °C in 5 times repeated batch of thermohydrolysis of cassava starch. The catalyst was studied for its potential role in the hydrolysis of cassava starch as a standard feedstock. It was shown that the milling of cassava starch in the presence of the CC-SO3H catalyst improved the solid-state reaction that enhanced porosity, increased surface area and decreased crystallinity of the starch granules. These phenomena caused the rapid thermohydrolysis of starch with an exceptionally high starch conversion rate (96.43%), glucose yield (93.12%), and glucose selectivity (95.32%) within 2 h of reaction at 160 "C, 10 bar. The highest ethanol yield (0.43 g ethanol/g total reducing sugars) was achieved at 96 h of fermentation corresponding to the highest ethanol concentration of 15.41 g/L from the fermentation of hydrolysate of mixed-milling/thermo-hydrolysis at 160 C for 2 h of cassava starch. In addition, the reaction kinetics showed the feasibility of this process for robust bioethanol production from starchy feedstocks. [ABSTRACT FROM AUTHOR]

Highlights • Ratio of α-amylase to glucoamylase is important in saccharifying cassava pulp (CP). • Cold hydrolysis at 50 °C followed by 30 °C is effective in CP saccharification. • A model was developed for predicting the performance of cold hydrolysis process. • A sequential process for bioconversion of CP to ethanol was proposed. • The proposed process yielded 27.4 g-ethanol/L, with 57.8% fermentation efficiency. Abstract The present study investigated cold hydrolysis of cassava pulp (CP) and the use of cold hydrolysis with simultaneous saccharification and fermentation (SSF) for ethanol production. Cold hydrolysis of 100 g-CP/L at 50 °C for 2 h, followed by at 30 °C for 72 h resulted in the production of 71.5 ± 1.8 g/L of reducing sugar, with a yield of 0.72 g/g-CP. A mathematical model describing the cold hydrolysis process was subsequently developed. The model proved to be applicable for other cold hydrolysis systems with satisfactory results. The sequential process of cold hydrolysis at 50 °C for 2 h, followed by SSF at 30 °C for 72 h gave 27.4 g-ethanol/L, with a productivity of 0.37 g/(L h) and a fermentation efficiency of 57.58%. Based on the results, a bioconversion process for CP to ethanol was proposed. In this process, 1 kg of ethanol could be produced from 3.65 kg of CP without any nutrient supplementation. [ABSTRACT FROM AUTHOR]

Highlights • Lignocellulosic waste can serve as a microbial carrier in bioconversion processes. • Lignocellulosic carriers were hydrothermally modified for microbial immobilization. • Specific surface area and porosity of corn stalks were improved by the modification. • Conditions of 200 °C for 20 min with a 1 cm size were optimal for modifying the carriers. • Modified carriers showed better immobilization and ethanol fermentation performance. Abstract Microbial immobilization is a key approach to enhance fermentation performance, especially with the advantages of low costs and the good surface properties of the lignocellulosic wastes, which can serve as natural carriers. This study investigated the capability of hydrothermal modification to improve the physicochemical properties of corn stalk carriers for microbial immobilization. Hydrothermal modification can degrade lignocellulosic structure by dissolving part of the components at different conditions. A temperature of 200 °C for 20 min with a carrier side length of 1 cm were selected as the optimal modification conditions. With these conditions, the specific surface area and porosity of the modified corn stalk carriers were 2.44 m2/g and 0.011 cm3/g, respectively, which were twice the values of untreated carriers. Immobilization tests showed that bacteria and yeast grew stably inside the modified carriers and that the immobilized biomass was 49% greater than that of the untreated carriers. After fermentation with bacteria, ethanol production in the modified carrier system was increased by 57% and 99% compared to the untreated carrier system and free bacteria, respectively. These findings confirmed that hydrothermal modification is efficient to improve lignocellulosic carrier properties to achieve better immobilization and fermentation performance, thus benefiting to the utilization of lignocellulosic wastes and their bioconversion processes. [ABSTRACT FROM AUTHOR]

Highlights • A continuous fermentation process with a delayed product inhibition is considered. • Stability analysis of the control system with PI algorithm and process delay is given. • The negative effect of measurement noises is considered. • The process is stabilized for any delay and for a sufficiently high controller gain. • Filtering of the process variable reduces the effect of noises, but affects stability. Abstract The paper addresses the problem of stabilization of ethanol concentration in continuous fermentation processes. The stability analysis is performed for a class of continuous fermentation processes assuming that the possible oscillatory behavior results from a delayed response of microorganisms to inhibitory effects of ethanol concentration and that the specific growth rate is a monotonic function of substrate and a monotonic function of product concentrations. Treating dilution rate as the manipulated variable, it is shown that the classical PI controller is able to stabilize the oscillating process in the whole range of operating regions. Moreover, for a sufficiently large controller gain, the closed-loop system is asymptotically stable for any process delay. However, a high-gain controller may lead to extensive control signal activity and wear of actuator in the presence of measurement noises. To reduce the negative effect of measurement noises, the measured process variable is filtered by using the first order filter. Then, it is shown that the closed-loop system with the filter can also be stabilized for any process delay. The simulation results confirmed the effectiveness of the proposed closed-loop strategy with and without filtering. [ABSTRACT FROM AUTHOR]

Highlights • Alkali and acid pretreated biomass slurries were mixed for ethanol production. • This approach saved 40–50% alkali/acid use. • This approach improved fermentability. Abstract Alkali and acid pretreatment based processes for lignocellulosic biofuel production typically consume substantial amount of alkali and acid. In addition, alkali pretreatment generates compounds with high toxicity rendering washing/detoxification inevitable. In this work, alkali (AL) and dilute acid (DA) pretreatment based processes were compared side by side for ethanol production from corn stover (CS) using commercial enzymes and Zymomonas mobilis 8b strain. Next, AL and DA pretreated CS slurries (without removing liquid stream) were mixed to neutralize for enzymatic hydrolysis and ethanol fermentation. The digestibility and fermentability of the mixed pretreated biomass were systematically studied and compared to unmixed pretreated biomass. Results showed that mixed biomass process saved 40–50% alkali/acid use and enhanced fermentability compared to AL-CS. This work suggests that it could be beneficial to have both alkali and acid pretreatments operating in a biorefinery, which could accommodate various feedstocks. [ABSTRACT FROM AUTHOR]

Lignocellulosic materials are good feedstocks for ethanol production. Mathematical models give information about kinetic-metabolic nature of fermentation. The objectives of this study were to determine the chemical composition of non-detoxified tea processing waste hydrolysate (ND-TPWH) and detoxified tea processing waste hydrolysate (D-TPWH), to generate the ethanol from the D-TPWH, and to model the ethanol fermentation in D-TPWH using models including modified Gompertz, re-modified Gompertz, modified logistic, re-modified logistic, modified Richards, re-modified Richards, Stannard, Baranyi, Weibull, and Morgan-Mercer-Flodin. Results indicated that 11.91% of d -glucuronic acid, 7.28% of acetic acid, 98.12% of hydroxymethylfurfural, and 76.88% of phenolics were adsorbed by detoxification process. Ethanol yields by Saccharomyces cerevisiae and Scheffersomyces stipitis (ATCC 58784 and ATCC 58785) were 35.9, 38.98, and 33.87%, respectively. Regarding modeling, depending on the model comparison results including root-mean-square-error, mean-absolute-error, and regression coefficient, the experimental data of ethanol production and sugar consumption were successfully forecasted using Baranyi and Weibull models for S. cerevisiae ; using Morgan-Mercer-Flodin model for S. stipitis (ATCC 58784); and using Stannard model for S. stipitis (ATCC 58785), respectively. Consequently, this was the first report on the ethanol production from D-TPWH and its modeling. TPW can be a good feedstock for ethanol production by the xylose-fermenting yeasts. Suitable flexible models could be applied for more progress of ethanol production process in D-TPWH. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Content of higher alcohols is closely related to the type of raw material used. • Trace-amount alcohols are mainly associated with method of starch liberation. • Initial pH of sweet mashes has an effect on the content of 1- and 2-propanol. Abstract The qualitative and quantitative profile of volatile compounds in agricultural distillate depends on numerous factors. Many such compounds, including higher alcohols, occur naturally, due to the metabolism of yeast during ethanol fermentation. Some are difficult to remove in the rectification process. For these reasons, it is desirable to reduce the synthesis of volatile compounds, among others higher alcohols, during the fermentation process. The results of the presented study showed that the raw materials, the method of starch liberation, and the initial pH of the sweet mashes affected the concentrations of higher alcohols in the distillates. Higher concentrations of 1-butanol, 1-propanol, and 2-propanol were found in distillates obtained from mashes prepared by the thermal-pressure method, while the remaining compounds occurred at higher concentrations in distillates obtained using the pressureless starch liberation method. The type of raw materials used had an influence on the concentration of the majority of higher alcohols. The content of 2-propanol, 2-methyl-1-propanol, 1-propanol, 1-butanol, 3-methyl-1-butanol, and 2-phenylethanol was lower in distillates obtained from mashes with an initial pH of 4, in comparison with those obtained from mashes with the pH set at 5.5. [ABSTRACT FROM AUTHOR]

Maize starch was irradiated by a Co60 irradiator with different doses. The morphology and physicochemical properties of native and irradiated starches were investigated. Scanning electron microscopy showed that the shape and size of starch granules did not change after irradiation. However, the irradiated starch granules were easily destroyed by dissolution. Irradiation also caused the change of starch color, the decrease in the pH value, light transmittance, stability index, degree of polymerization, total sugar content, and the increase in the swelling index and the reducing sugar content. In this study, irradiated maize starch was also used as material for ethanol fermentation to investigate its potential as a pretreatment method. Results showed that the ethanol yield of cooked and raw starch fermentation using irradiated starch increased by 20.41 % and 5.18 %, respectively, and the ethanol concentration increased by 3 % and 2 %. This finding indicated that irradiation effectively improved the utilization rate of maize starch, making it an effective pretreatment method for ethanol fermentation. [ABSTRACT FROM AUTHOR]

Background: Future biorefineries will focus on converting low value waste streams to chemical products that are derived from petroleum or refined sugars. Feedstock pretreatment in a simple, cost effective, agnostic manner is a major challenge. Methods: In this work, beechwood sawdust was delignified via an organosolv process, assisted by homogeneous inorganic acid catalysis. Mixtures of water and several organic solvents were evaluated for their performance. Specifically, ethanol (EtOH), acetone (AC), and methyl- isobutyl- ketone (MIBK) were tested with or without the use of homogeneous acid catalysis employing sulfuric, phosphoric, and oxalic acids under relatively mild temperature of 175 °C for one hour. Results: Delignification degrees (DD) higher than 90% were achieved, where both AC and EtOH proved to be suitable solvents for this process. Both oxalic and especially phosphoric acid proved to be good alternative catalysts for replacing sulfuric acid. High gravity simultaneous saccharification and fermentation with an enzyme loading of 8.4 mg/gsolids at 20 wt.% initial solids content reached an ethanol yield of 8.0 w/v%. Conclusions: Efficient delignification combining common volatile solvents and mild acid catalysis allowed for the production of ethanol at high concentration in an efficient manner. [ABSTRACT FROM AUTHOR]

During ethanol production, the ratio of various sources of starch-hydrolyzing enzymes significantly influences hydrolysis efficiency in a very high gravity (VHG) system. In this study, the enzyme matching approach was proposed to optimize liquefaction and saccharification yield of cassava root and cassava starch. For fresh cassava root, the synergistic effect of using Techzyme Q-Add enzyme (93 °C pH 5.6) for liquefaction and GC 147 enzyme (61.5 °C pH 4.2) for saccharification achieved the highest yield among all enzyme-matching designs. At 25% solid, highest total reducing sugar (TRS) yields from sequential liquefaction and saccharification of cassava starch, fresh cassava, and dry cassava were 87.9%, 85.1%, and 70.0% corresponding to 286.8, 249.4, and 241.1 g/L, respectively. For VHG ethanol fermentation by Saccharomyces cerevisiae TISTR 5606, separate liquefaction and simultaneous saccharification and fermentation (SLSSF) gave a significantly higher ethanol concentration compared with separate liquefaction and saccharification and fermentation (SLSF). From a 35% solid SLSSF system, the highest ethanol produced at 30 °C was 27.3 g/L from 72 h, respectively. The results suggested that SLSSF could effectively shorten the time course of the whole process for liquefaction, saccharification, and fermentation from 74 h to only 26 h for similar ethanol production yields. [ABSTRACT FROM AUTHOR]

In the present investigation, an collagen fibre (CF), abundant natural biomass, was successfully grafted by polyethyleneimine (PEI). The resultant PEI grafted collagen fibre (CF-PEI) was employed as biocompatible and high cell loading support matrix for the immobilization of Saccharomyces cerevisiae cells. The as-prepared CF-PEI immobilized cells (CF-PEI-cell) exhibited high activity and stability for both batch and continuous fermentation. In batch fermentation, CF-PEI-cells showed enhanced stability as compared with other matrices supported cells, and produced an average ethanol concentration of 45.04 g/L with ethanol yield (YP/S) of 0.46 g/g and glucose conversion efficiency (η) of 90.4%. Continuous fermentation was operated stably in a down-flow trickling bed reactor charged with CF-PEI-cell for a total of 2 months. When the dilution rate was 0.16 1/h, the average ethanol productivity reached 7.18 g/(L h) with η of 88.94%. Further scanning electron microscopy observations confirmed that yeast cells can proliferate on the surface of CF-PEI during ethanol fermentation, which demonstrates that CF-PEI is indeed an ideal matrix for the immobilization of yeast cells. [ABSTRACT FROM AUTHOR]

Background: High temperature inhibits cell growth and ethanol fermentation of Saccharomyces cerevisiae. As a complex phenotype, thermotolerance usually involves synergistic actions of many genes, thereby being difficult to engineer. The overexpression of either endogenous or exogenous stress-related transcription factor genes in yeasts was found to be able to improve relevant stress tolerance of the hosts. Results: To increase ethanol yield of high-temperature fermentation, we constructed a series of strains of S. cerevisiae by expressing 8 transcription factor genes from S. cerevisiae and 7 transcription factor genes from thermotolerant K. marxianus in S. cerevisiae. The results of growth curve measurements and spotting test show that KmHsf1 and KmMsn2 can enhance cell growth of S. cerevisiae at 40-42 °C. According to the results of batch fermentation at 43 °C with an initial glucose concentration of 104.8 g/l, the fermentation broths of KmHSF1 and KmMSN2-expressing strains could reach final ethanol concentrations of 27.2 ± 1.4 and 27.6 ± 1.2 g/l, respectively, while the control strain just produced 18.9 ± 0.3 g/l ethanol. Transcriptomic analysis found that the expression of KmHSF1 and KmMSN2 resulted in 55 (including 31 up-regulated and 24 down-regulated) and 50 (including 32 up-regulated and 18 down-regulated) genes with different expression levels, respectively (padj < 0.05). The results of transcriptomic analysis also reveal that KmHsf1 might increase ethanol production by regulating genes related to transporter activity to limit excessive ATP consumption and promote the uptake of glucose; while KmMsn2 might promote ethanol fermentation by regulating genes associated with glucose metabolic process and glycolysis/gluconeogenesis. In addition, KmMsn2 might also help to cope with high temperature by regulating genes associated with lipid metabolism to change the membrane fluidity. Conclusions: The transcription factors KmHsf1 and KmMsn2 of thermotolerant K. marxianus can promote both cell growth and ethanol fermentation of S. cerevisiae at high temperatures. Different mechanisms of KmHsf1 and KmMsn2 in promoting high-temperature ethanol fermentation of S. cerevisiae were revealed by transcriptomic analysis. [ABSTRACT FROM AUTHOR]

Garcinia cambogia, a Chinese herbal medicine, was popular due to its effect for weight loss. The main medical component inside was determined to be hydroxycitric acid (HCA). To realize the resource technology of garcinia cambogia residue, Optimum ethanol production from residues was investigated, and the effects of remaining HCA on the ethanol yield were investigated. A Plackett-Burman experimental design was used to screen the significance of several influencing factors, and cellulase, yeast extract, and KH2PO4 were observed to exert important effects. The optimum ethanol fermentation conditions were determined through an orthogonal design to include a cellulase concentration of 100 U/g, a yeast extract concentration of 15 g/L, and a KH2PO4 concentration of 1.0 g/L. The ethanol concentration obtained under optimal conditions was 4.0 g/L. The remained HCA in the residues showed minimal influences on ethanol fermentation and could even increase ethanol yield at low concentrations. [ABSTRACT FROM AUTHOR]

Imazamox and glyphosate represent two classes of herbicides that inhibit the activity of acetohydroxyacid synthase in the branched-chain amino acid biosynthesis pathway and the activity of 5-enolpyruvylshikimate-3-phosphate synthase in the aromatic amino acid biosynthesis pathway, respectively. However, it is still unclear how imazamox and glyphosate lead to plant death. Both herbicides inhibit amino-acid biosynthesis and were found to induce ethanol fermentation in plants, but an Arabidopsis mutant deficient in alcohol dehydrogenase 1 was neither more susceptible nor more resistant than the wild-type to the herbicides. In this study, we investigated the effects of the amino acid biosynthesis inhibitors, imazamox and glyphosate, on the pyruvate dehydrogenase bypass reaction and fatty acid metabolism in A. thaliana . We found that the pyruvate dehydrogenase bypass was upregulated following the treatment by the two herbicides. Our results suggest that the Arabidopsis aldehyde dehydrogenase 7B4 gene might be participating in the pyruvate dehydrogenase bypass reaction. We evaluated the potential role of the aldehyde dehydrogenase 7B4 upon herbicide treatment in the plant defence mechanism. Plants that overexpressed the ALDH7B4 gene accumulated less soluble sugars, starch, and fatty acids and grew better than the wild-type after herbicide treatment. We discuss how the upregulation of the ALDH7B4 alleviates the effects of the herbicides, potentially through the detoxification of the metabolites produced in the pyruvate dehydrogenase bypass. [ABSTRACT FROM AUTHOR]

In this study, it was found that the type of phenolic acids derived from rice straw was the major factor affecting ethanol fermentation by Pichia stipitis . The aim of this study was to investigate the inhibitory effect of phenolic acids on ethanol fermentation with rice straw. Different cellulases produced different ratios of free phenolic acids to soluble conjugated phenolic acids, resulting in different fermentation efficiencies. Free phenolic acids exhibited much higher inhibitory effect than conjugated phenolic acids. The flow cytometry results indicated that the damage to cell membranes was the primary mechanism of inhibition of ethanol fermentation by phenolic acids. The removal of free phenolic acids from the hydrolysates increased ethanol productivity by 2.0-fold, indicating that the free phenolic acids would be the major inhibitors formed during saccharification. The integrated process for ethanol and phenolic acids may constitute a new strategy for the production of low-cost ethanol. [ABSTRACT FROM AUTHOR]

Background: Multiple lignocellulose-derived inhibitors represent great challenges for bioethanol production from lignocellulosic materials. These inhibitors that are related to the levels of intracellular reactive oxidative species (ROS) make oxidoreductases a potential target for an enhanced tolerance in yeasts. Results: In this study, the thioredoxin and its reductase from Kluyveromyces marxianus Y179 was identified, which was subsequently achieved over-expression in Saccharomyces cerevisiae 280. In spite of the negative effects by expression of thioredoxin gene (KmTRX), the thioredoxin reductase (KmTrxR) helped to enhance tolerance to multiple lignocellulose- derived inhibitors, such as formic acid and acetic acid. In particular, compared with each gene expression, the double over-expression of KmTRX2 and KmTrxR achieved a better ethanol fermentative profiles under a mixture of formic acid, acetic acid, and furfural (FAF) with a shorter lag period. At last, the mechanism that improves the tolerance depended on a normal level of intracellular ROS for cell survival under stress. Conclusions: The synergistic effect of KmTrxR and KmTRX2 provided the potential possibility for ethanol production from lignocellulosic materials, and give a general insight into the possible toxicity mechanisms for further theoretical research. [ABSTRACT FROM AUTHOR]

Miscanthus × giganteus is a perennial rhizomatous grass which is used as a biofuel crop. Due to its high yields, low production costs, resistance to low temperatures, low soil requirements and, above all, high cellulose content, miscanthus can be a useful resource for ethanol production. The aim of this study was to determine the effect of two fertilization regimes (sewage sludge/mineral NPK) during miscanthus cultivation on the chemical composition of biomass, the content of major lignocellulosic factions and the effectiveness of miscanthus conversion to bioethanol. The results indicate that fertilization treatments influenced biomass yield and the content of major lignocellulosic fractions. Bioethanol production was higher when hydrolysis and fermentation processes were conducted separately than when saccharification and fermentation were conducted simultaneously. Ethanol production increased by 30% and 40% in response to sewage sludge and NPK (equivalent nitrogen content = 160 kg N/ha) fertilization, respectively, in comparison with unfertilized crops. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the influence of different starch liberation and saccharification methods on microbiological contamination of distillery mashes. Moreover, the effect of hop α-acid preparation for protection against microbial infections was assessed. The quality of agricultural distillates was also evaluated. When applying the pressureless liberation of starch (PLS) and malt as a source of amylolytic enzymes, the lactic acid bacteria count in the mashes increased several times during fermentation. The mashes obtained using the pressure-thermal method and malt enzymes revealed a similar pattern. Samples prepared using cereal malt exhibited higher concentrations of lactic and acetic acids, as compared to mashes prepared using enzymes of microbial origin. The use of hop α-acids led to the reduction of bacterial contamination in all tested mashes. As a result, fermentation of both mashes prepared with microbial origin enzyme preparations and with barley malt resulted in satisfactory efficiency and distillates with low concentrations of aldehydes. [ABSTRACT FROM AUTHOR]

In this study, dilute alkali salts (0.6% NaClO, 0.067% Na 2 S) pretreatment at 10% sulfidity under the autoclave system at 120 °C for 40 min was used for pretreating bamboo shoot shell (BSS). Furthermore, FT-IR, XRD and SEM were employed to characterize the changes in the cellulose structural characteristics (porosity, morphology, and crystallinity) of the pretreated BSS solid residue. After 72 h, the reducing sugars and glucose from the enzymatic in situ hydrolysis of 50 g/L pretreated BSS in dilute NaClO/Na 2 S media could be obtained at 31.11 and 20.32 g/L, respectively. Finally, the obtained BSS-hydrolysates containing alkalic salt NaClO/Na 2 S resulted in slightly negative effects on the ethanol production. Glucose in BSS-hydrolysates was fermented from 20.0 to 0.17 g/L within 48 h, and an ethanol yield of 0.41 g/g glucose, which represents 80.1% of the theoretical yield, was obtained. This study provided an effective strategy for potential utilization of BSS. [ABSTRACT FROM AUTHOR]

Bio-ethanol used today is mainly produced from sugar cane and cereals, but reducing the production costs of ethanol is still crucial for a viable economic process. Cellulose from plant biomass will be the next cheaper raw material for second generation fuel ethanol production. Saccharomyces cerevisiae and Schizosaccharomyces pombae are the common industrial yeast strains used for the production of ethanol from various substrates derived from agricultural commodities. In the present study, ethanol was produced from various substrates such as molasses, sugarcane juice, sugarcane syrup, jaggery, grapes, beet root, orange and rice substrates by using Saccharomyces cerevisiae and Schizosaccharomyces pombae. The experimental study shows that the biomass production declines progressively when the ethanol accumulates in the surrounding medium after the production of ethanol. However, the conversion of ethanol was achieved in batch fermentation process at optimum temperature and the internal pH of the fermentation medium at laboratory level. The yield percentage of ethanol for the above substrates were analyzed and compared for different carbon sources. Among different substrates, Jaggery and Molases showed higher ethanol yield as 95.2% and 93.5% respectively. Among the two species of yeast studied, Saccharomyces cerevisiae yielded higher percentage of ethanol than Schizosaccharomyces pombae in batch fermentation process. The present study concludes the effect of various carbon sources on production of ethanol with two different industrial yeast strains such as Saccharomyces cerevisiae and Schizosaccharomyces pombae are vary in similar conditions of ethanol production processprocess. [ABSTRACT FROM AUTHOR]

We previously showed that overexpression of IoGAS1 , which was isolated from the multiple stress-tolerant yeast Issatchenkia orientalis , endows Saccharomyces cerevisiae cells with the ability to grow and ferment under acidic and high-salt conditions. The deduced amino acid sequence of the IoGAS1 gene product exhibits 60% identity with the S . cerevisiae Gas1 protein, a glycosylphosphatidylinositol-anchored protein essential for maintaining cell wall integrity. However, the functional roles of ScGAS1 in stress tolerance and pH regulation remain unclear. In the present study, we characterized ScGAS1 regarding its roles in tolerance to low pH and high salt concentrations. Transcriptional analysis indicated that, as for the IoGAS1 gene, ScGAS1 expression was pH dependent, with maximum expression at pH 3.0; the presence of salt increased endogenous expression of both GAS1 genes at almost all pH levels. These results suggested that ScGAS1 , like IoGAS1 , is involved in a novel acid- and salt-stress adaptation mechanism in S . cerevisiae . Overexpression of ScGAS1 in S . cerevisiae improved growth and ethanol production from glucose under acid stress without added salt, although the stress tolerance of the ScGAS1 -overexpressing strain was inferior to that of the IoGAS1 -overexpressing strain. However, overexpression of ScGAS1 did not result in increased tolerance of S . cerevisiae to combined acid and salt stress, even though ScGAS1 appears to be a salt-responsive gene. Thus, ScGAS1 is directly implicated in tolerance to low pH but does not confer salinity tolerance, supporting the view that ScGAS1 and IoGAS1 have overlapping yet distinct roles in stress tolerance in yeast. [ABSTRACT FROM AUTHOR]

Forward osmosis (FO), driven by high osmotic pressure, was used for the first time for bioethanol production from lignocellulosic biomass. A commercial membrane, TFC-ES (Hydration Technology Innovation), was used and 3.6 M triethylamine (TEA) was chosen as the draw solution because the concentration ratio against a model xylose solution was similar to that achieved with 2.5 M NaCl. The liquid fraction of hot-water-pretreated rice straw was concentrated by using the FO membrane. The initial sugar concentration of 199 mM increased to 825 and 1612 mM after 48 and 72 h of FO concentration, respectively, and these values were much higher than those obtained from nanofiltration. Simultaneous saccharification and fermentation of the liquid fraction after 48 h of FO concentration by xylose-fermenting recombinant Saccharomyces cerevisiae produced 17.7 g/L of ethanol after 24 h fermentation. Thus, the FO process has tremendous potential to up-concentrate sugars obtained from lignocellulosic biomass. [ABSTRACT FROM AUTHOR]

Methane and ethanol were co-produced from different feedstock, including a mixture of dairy manure and soybean straw (DMS), a mixture of pig manure and soybean straw (PMS), and soybean straw alone (SS), after anaerobic digestion times of 30 and 60 days in mesophilic conditions. Digesting DMS for 60 days led to the highest methane yield of 115.3 g/kg dry raw feed; however, the lowest ethanol yield of 88 g/kg dry raw feed was observed. After 30 days, SS yielded the lowest methane levels (45.2 g/kg dry raw feed) but the highest ethanol levels (113.5 g/kg dry raw feed). Analysis of the net energy balance showed that the highest net energy balance, 6549 kJ/kg of dry raw feedstock, was achieved from the digestion of DMS for 60 days. Overall, both the type of feedstock and length of digestion time played important roles in the integrated processing of methane and ethanol from livestock manure and straw. [ABSTRACT FROM AUTHOR]

Background: Bioethanol from lignocellulosic materials is of great significance to the production of renewable fuels due to its wide sources. However, multiple inhibitors generated from pretreatments represent great challenges for its industrial-scale fermentation. Despite the complex toxicity mechanisms, lignocellulose-derived inhibitors have been reported to be related to the levels of intracellular reactive oxygen species (ROS), which makes oxidoreductase a potential target for the enhancement of the tolerance of yeasts to these inhibitors. Results: A typical 2-Cys peroxiredoxin from Kluyveromyces marxianus Y179 (KmTPX1) was identified, and its overexpression was achieved in Saccharomyces cerevisiae 280. Strain TPX1 with overexpressed KmTPX1 gene showed an enhanced tolerance to oxidative stresses. Serial dilution assay indicated that KmTPX1 gene contributed to a better cellular growth behavior, when the cells were exposed to multiple lignocellulose-derived inhibitors, such as formic acid, acetic acid, furfural, ethanol, and salt. In particular, KmTPX1 expression also possessed enhanced tolerance to a mixture of formic acid, acetic acid, and furfural (FAF) with a shorter lag period. The maximum glucose consumption rate and ethanol generation rate in KmTPX1-expressing strain were significantly improved, compared with the control. The mechanism of improved tolerance to FAF depends on the lower level of intracellular ROS for cell survival under stress. Conclusion: A new functional gene KmTPX1 from K. marxianus is firstly associated with the enhanced tolerance to multiple lignocellulose-derived inhibitors in S. cerevisiae. We provided a possible detoxification mechanism of the KmTPX1 for further theoretical research; meanwhile, we provided a powerful potential for application of the KmTPX1 overexpressing strain in ethanol production from lignocellulosic materials. [ABSTRACT FROM AUTHOR]

Since both ethanol and butanol fermentations are urgently developed processes with the biofuel-demand increasing, performance comparison of aerobic ethanol fermentation and anerobic butanol fermentation in a continuous and closed-circulating fermentation (CCCF) system was necessary to achieve their fermentation characteristics and further optimize the fermentation process. Fermentation and pervaporation parameters including the average cell concentration, glucose consumption rate, cumulated production concentration, product flux, and separation factor of ethanol fermentation were 11.45 g/L, 3.70 g/L/h, 655.83 g/L, 378.5 g/m2/h, and 4.83, respectively, the corresponding parameters of butanol fermentation were 2.19 g/L, 0.61 g/L/h, 28.03 g/L, 58.56 g/m2/h, and 10.62, respectively. Profiles of fermentation and pervaporation parameters indicated that the intensity and efficiency of ethanol fermentation was higher than butanol fermentation, but the stability of butanol fermentation was superior to ethanol fermentation. Although the two fermentation processes had different features, the performance indicated the application prospect of both ethanol and butanol production by the CCCF system. [ABSTRACT FROM PUBLISHER]

Background: Lignocellulosic biomass is an abundant and inexpensive resource for biofuel production. Alongside its biotechnological conversion, pretreatment is essential to enable efficient enzymatic hydrolysis by making cellulose susceptible to cellulases. Wet oxidation of biomass, such as acetone/water oxidation, that employs hot acetone, water, and oxygen, has been found to be an attractive pretreatment method for removing lignin while producing less degradation products. The remaining enriched cellulose fraction has the potential to be utilized under high gravity enzymatic saccharification and fermentation processes for the cost-competing production of bioethanol. Results: Beech wood residual biomass was pretreated following an acetone/water oxidation process aiming at the production of high concentration of cellulosic ethanol. The effect of pressure, reaction time, temperature, and acetone-to-water ratio on the final composition of the pretreated samples was studied for the efficient utilization of the lignocellulosic feedstock. The optimal conditions were acetone/water ratio 1:1, 40 atm initial pressure of 40 vol% O2 gas, and 64 atm at reaction temperature of 175 °C for 2 h incubation. The pretreated beech wood underwent an optimization step studying the effect of enzyme loading and solids content on the enzymatic liquefaction/saccharification prior to fermentation. In a custom designed free-fall mixer at 50 °C for either 6 or 12 h of prehydrolysis using an enzyme loading of 9 mg/g dry matter at 20 wt% initial solids content, high ethanol concentration of 75.9 g/L was obtained. Conclusion: The optimization of the pretreatment process allowed the efficient utilization of beech wood residual biomass for the production of high concentrations of cellulosic ethanol, while obtaining lignin that can be upgraded towards high-added-value chemicals. The threshold of 4 wt% ethanol concentration that is required for the sustainable bioethanol production was surpassed almost twofold, underpinning the efficient conversion of biomass to ethanol and bio-based chemicals on behalf of the biorefinery concept. [ABSTRACT FROM AUTHOR]

Two different plants namely Phoenix canariensis and Opuntia ficus-indica were used as substrate for reducing sugar generation and ethanol production. Dilute acid, alkaline and steam explosion were used as pretreatment methods in order to depolymerize lignin and/or hemicellulose and recover cellulose. By using alkaline pretreatment with 2.5% NaOH 71.08% for P. canariensis and 74.61% for O. ficus-indica lignin removal and 81.84% for P. canariensis and 72.66% for O. ficus-indica cellulose recovery yields were obtained. Pretreated materials were hydrolyzed by cellulase with high efficiency (87.0% and 84.5% cellulose conversion yields for P. canariensis and O. ficus-indica ) and used as substrate for fermentation. Maximum ethanol production of 15.75 g/L and 14.71 g/L were achieved from P. canariensis and O. ficus-indica respectively. Structural differences were observed by XRD, FTIR and SEM for untreated, pretreated, hydrolyzed and fermented samples and were highly correlated with compositional analysis results. [ABSTRACT FROM AUTHOR]

An oxidative production process of xylonic acid using xylose in distillation stillage of cellulosic ethanol fermentation broth was designed, experimentally investigated, and evaluated. Dry dilute acid pretreated and biodetoxified corn stover was simultaneously saccharified and fermented into 59.80 g/L of ethanol (no xylose utilization). 65.39 g/L of xylose was obtained in the distillation stillage without any concentrating step after ethanol was distillated. Then the xylose was completely converted into 66.42 g/L of xylonic acid by Gluconobacter oxydans . The rigorous Aspen Plus modeling shows that the wastewater generation and energy consumption was significantly reduced comparing to the previous xylonic acid production process using xylose in pretreatment liquid. This study provided a practical process option for xylonic acid production from lignocellulose feedstock with significant reduction of wastewater and energy consumption. [ABSTRACT FROM AUTHOR]

Methane and ethanol were co-produced from different feedstock, including a mixture of dairy manure and soybean straw (DMS), a mixture of pig manure and soybean straw (PMS), and soybean straw alone (SS), after anaerobic digestion times of 30 and 60 days in mesophilic conditions. Digesting DMS for 60 days led to the highest methane yield of 115.3 g/kg dry raw feed; however, the lowest ethanol yield of 88 g/kg dry raw feed was observed. After 30 days, SS yielded the lowest methane levels (45.2 g/kg dry raw feed) but the highest ethanol levels (113.5 g/kg dry raw feed). Analysis of the net energy balance showed that the highest net energy balance, 6549 kJ/kg of dry raw feedstock, was achieved from the digestion of DMS for 60 days. Overall, both the type of feedstock and length of digestion time played important roles in the integrated processing of methane and ethanol from livestock manure and straw. [ABSTRACT FROM AUTHOR]

In this study, soluble polysaccharides (SPs) were used to prepare the complexes with different degrees of polymerization and ratios of saccharide to phenolic acids (PAs) and their effects on yeast growth and ethanol fermentation were studied. Time-of-flight mass spectrometry showed that the lower the degree of saccharide polymerization, the higher the PA content. Oligosaccharide-PAs played an important role in ethanol fermentation. ATP/ADP and flow cytometry indicated that oligosaccharide-PAs could improve cell viability and increase the proportion of living and dead cells. Atomic force microscopy and confocal laser scanning microscopy images showed that the oligosaccharide-PAs induced the formation of extracellular matrixes, maintained the cellular biomorphology. The oligosaccharide-PAs also regulated NAD+/NADH, NAPD+/NADPH, and reduced the intracellular peroxide content. Thus, the oligosaccharide-PAs improved the cell viability by reducing the intracellular peroxide content and maintaining the cellular biomorphology. [Display omitted] • Saccharide polymerization has a strong correlation with the ratio of saccharide to PAs. • Oligosaccharides-PAs complex had a stronger effect than SPs on ethanol fermentation. • The complex can reduce intracellular peroxide content and maintain cell morphology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Rice husk improves yeast tolerance to high temperature and ethanol concentration. • Yeast biofilms on rice husks tolerate high temperature and ethanol concentration. • Kinetic models illustrate the promotion of fermentation by rice husk. • A mixed substrate was applied in the ethanol fermentation. In recent years, growing attention has been devoted to improving stress resistance of yeast to temperature and ethanol concentration as it affects fermentation productivity in biofuel ethanol industry. Rice husk was found to increase the resistance of yeast to high temperature and high ethanol concentration, which can be attributed to yeast cell adsorption on rice husk. Compared with no addition of rice husk, the ethanol yield of brown rice fermented at 32 °C and 39 °C with 1.0 % rice husk increased by 9.4 % and 5.1 %. The fermentation kinetics of cell growth and ethanol formation could be described by the improved Logistic model and Luedeking-Piret model, respectively. Based on the effect of rice husk, the higher ethanol concentration (106.7 g/L at 32 °C) and complete substrate utilization could be achieved by using a mixed substrate at dry mass ratio of whole rice to brown rice of 3:1. [ABSTRACT FROM AUTHOR]

[Display omitted] • Whole-cell biomass utilization was completed with newly integrated biorefinery. • Hydrolysis yielded 89 % of total carbohydrate within 4 min using optimized process. • Volume reduction decreased solvent usage by 75 % and recovered all oil within 20 min. • Bioethanol yield of sole hydrolysate was comparable with conventional YPD medium. • Newly developed process decreased OPEX and CAPEX by 82.7 % and 70.1 %, respectively. Microalgae are a promising source of biomass for the production of biofuels, but their use is currently infeasible because of changes in the biofuel market and the lack of an optimized refinery process. The biomass of oleaginous microalgae consists of up to 50% lipids and 50% carbohydrates and proteins, so the biorefinery process must be able to use whole cell biomass. In this work, an alternative process to the standard biorefinery approach of lipid extraction and treatment of lipid-extracted residue was developed and tested using oleaginous Chlorella sp. ABC-001. First, a hydrolysis process was optimized to achieve cell lysis. At 170 °C and 0.1 N H 2 SO 4 , 89.0% of total carbohydrates were hydrolyzed to monosaccharides within 4 min. Then, a volume reduction process (brief and mild centrifugation) was applied to reduce the extraction time and the use of organic solvent. By reducing the aqueous phase from the hydrolysate, all lipids were extracted by vortexing with just a quarter of the original volume (10 mL) within 20 min. Finally, after extraction the aqueous phase was utilized as the sole growth medium for ethanol production by Saccharomyces cerevisiae KL17. The resulting ethanol yield was 0.39 g ethanol/g sugar, comparable to that achieved using conventional yeast-peptone-dextrose (YPD) medium (0.41 g ethanol/g sugar). Furthermore, relative to the conventional process, techno-economic analysis confirmed that the newly developed process decreased operational expenditures by 82.7% and decreased capital expenditures by 70.1%. [ABSTRACT FROM AUTHOR]

Most of ethanol production processes are limited by lower ethanol production rate and recyclability problem of ethanologenic organism. In the present study, immobilized co-fermenting Saccharomyces cerevisiae GSE1618 was employed for ethanol fermentation using rice straw enzymatic hydrolysate in a packed bed reactor (PBR). The immobilization of S . cerevisiae was performed by entrapment in Ca-alginate for optimization of ethanol production by varying alginic acid concentration, bead size, glucose concentration, temperature and hardening time. Remarkably, extra hardened beads (EHB) immobilized with S . cerevisiae could be used up to repeated 40 fermentation batches. In continuous PBR, maximum 81.82 g L −1 ethanol was obtained with 29.95 g L −1 h −1 productivity with initial glucose concentration of 180 g L −1 in feed at dilution rate of 0.37 h −1 . However, maximum ethanol concentration of 40.33 g L −1 (99% yield) with 24.61 g L −1 h −1 productivity was attained at 0.61 h −1 dilution rate in fermentation of un-detoxified rice straw enzymatic hydrolysate (REH). At commercial scale, EHB has great potential for continuous ethanol production with high productivity using lignocellulosic hydrolysate in PBR. [ABSTRACT FROM AUTHOR]

Jerusalem artichoke (JA) is a potential energy crop for biorefinery due to its unique agronomic traits such as resistance to environmental stresses and high biomass yield in marginal lands. Although JA tubers have been explored for inulin extraction and biofuels production, there is little concern on its stalk (JAS). In this article, the pretreatment of JAS by alkaline hydrogen peroxide was optimized using the response surface methodology to improve sugars yield and reduce chemicals usage. Scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis were applied to characterize the structures of the pretreated JAS to evaluate the effectiveness of the pretreatment. Furthermore, the feeding of the pretreated JAS and cellulase was performed for high solid uploading (up to 30%) to increase ethanol titer, and simultaneous saccharification and fermentation with 55.6 g/L ethanol produced, 36.5% more than that produced through separate hydrolysis and fermentation, was validated to be more efficient. [ABSTRACT FROM AUTHOR]

Background: The induction of alcohol fermentation in roots is a plant adaptive response to flooding stress and oxygen deprivation. Available transcriptomic data suggest that fermentation-related genes are also frequently induced in roots infected with gall forming pathogens, but the biological significance of this induction is unclear. In this study, we addressed the role of hypoxia responses in Arabidopsis roots during infection by the clubroot agent Plasmodiophora brassicae. Results: The hypoxia-related gene markers PYRUVATE DECARBOXYLASE 1 (PDC1), PYRUVATE DECARBOXYLASE 2 (PDC2) and ALCOHOL DEHYDROGENASE 1 (ADH1) were induced during secondary infection by two isolates of P. brassicae, eH and e2. PDC2 was highly induced as soon as 7 days post inoculation (dpi), i.e., before the development of gall symptoms, and GUS staining revealed that ADH1 induction was localised in infected cortical cells of root galls at 21 dpi. Clubroot symptoms were significantly milder in the pdc1 and pdc2 mutants compared with Col-0, but a null T-DNA insertional mutation of ADH1 did not affect clubroot susceptibility. The Arg/N-end rule pathway of ubiquitin-mediated proteolysis controls oxygen sensing in plants. Mutants of components of this pathway, ate1 ate2 and prt6, that both exhibit constitutive hypoxia responses, showed enhanced clubroot symptoms. In contrast, gall development was reduced in quintuple and sextuple mutants where the activity of all oxygen-sensing Group VII Ethylene Response Factor transcription factors (ERFVIIs) is absent (erfVII and prt6 erfVII). Conclusions: Our data demonstrate that the induction of PDC1 and PDC2 during the secondary infection of roots by P. brassicae contributes positively to clubroot development, and that this is controlled by oxygen-sensing through ERFVIIs. The absence of any major role of ADH1 in symptom development may also suggest that PDC activity could contribute to the formation of galls through the activation of a PDH bypass. [ABSTRACT FROM AUTHOR]

In this study, repeated-batch fermentations in a biofilm reactor were evaluated for ethanol production from non-sterile enriched (NSE) and non-sterile non-enriched (NSNE) carob extracts by usingSaccharomyces cerevisiae. For the NSE medium, the ethanol production (P) and yield (YP/S) were 18.46 g/L and 33.76%, respectively. However, for the NSNE medium,PandYP/Swere 19.57 g/L and 38.14%, respectively. Results indicated that cost-effective ethanol production from non-sterile carob extract (NSCE) can be successfully applied in a biofilm reactor regarding both energy cost and recovery time. [ABSTRACT FROM PUBLISHER]

One of the key processes in making beer is fermentation. In the fermentation process, brewer's yeast plays an essential role in both the production of ethanol and the flavor profile of beer. Therefore, the mechanism of ethanol fermentation by of brewer's yeast is attracting much attention. The high ethanol productivity of sake yeast has provided a good basis from which to investigate the factors that regulate the fermentation rates of brewer's yeast. Recent studies found that the elevated fermentation rate of sake Saccharomyces cerevisiae species is closely related to a defective transition from vegetative growth to the quiescent (G 0 ) state. In the present study, to clarify the relationship between the fermentation rate of brewer's yeast and entry into G 0 , we constructed two types of mutant of the bottom-fermenting brewer's yeast Saccharomyces pastorianus Weihenstephan 34/70: a RIM15 gene disruptant that was defective in entry into G 0 ; and a CLN3 Δ PEST mutant, in which the G 1 cyclin Cln3p accumulated at high levels. Both strains exhibited higher fermentation rates under high-maltose medium or high-gravity wort conditions (20° Plato) as compared with the wild-type strain. Furthermore, G 1 arrest and/or G 0 entry were defective in both the RIM15 disruptant and the CLN3 Δ PEST mutant as compared with the wild-type strain. Taken together, these results indicate that regulation of the G 0 /G 1 transition might govern the fermentation rate of bottom-fermenting brewer's yeast in high-gravity wort. [ABSTRACT FROM AUTHOR]

In this study, a Saccharomyces cerevisiae recombinant strain 14 was constructed through genome shuffling method by transferring the whole genomic DNA of Candida intermedia strain 23 into a thermo-tolerant S. cerevisiae strain. The recombinant strain 14 combined the good natures of both parent strains that efficiently produced ethanol from glucose and single cell protein from xylose with 54.6% crude protein and all essential amino acids except cysteine at 35 °C. Importantly, the recombinant strain 14 produced 64.07 g/L ethanol from 25% (w/v) NaOH-pretreated and washed corn stover with the ethanol yield of 0.26 g/g total stover by fed-batch simultaneous saccharification and fermentation and produced 66.50 g/L dry cell mass subsequently from the residual hydrolysate and ethanol. Therefore, this study represents a feasible method to comprehensively utilize hexose and pentose in lignocellulosic materials. [ABSTRACT FROM AUTHOR]

Stillage reflux fermentation in food waste ethanol fermentation could reduce sewage discharge but exert a harmful effect because of side-product accumulation. In this study, regulation methods based on metabolic regulation and side-product alleviation were conducted. Result demonstrated that controlling the proper oxidation–reduction potential value (−150 mV to −250 mV) could reduce the harmful effect, improve ethanol yield by 21%, and reduce fermentation time by 20%. The methods of adding calcium carbonate to adjust the accumulated lactic acid showed that ethanol yield increased by 17.3%, and fermentation time decreased by 20%. The accumulated glyceal also shows that these two methods can reduce the harmful effect. Fermentation time lasted for seven times without effect, and metabolic regulation had a better effect than side-product regulation. [ABSTRACT FROM AUTHOR]

The use of field beans, a non-food leguminous crop, was studied for ethanol, feed components and fungal biomass production. The seeds were hydrolyzed using enzymes or with combination of acid (H 3 PO 4 ) and alkaline (Ca(OH) 2 ) pretreatment and enzymatic hydrolysis. Fermentation by Saccharomyces cerevisiae , with or without removal of suspended solids, yielded 38.3–42.5 g L −1 ethanol (71.3–79.2% efficiency). The filtration residues contained ca. 247–326 g kg −1 crude protein, 10.6–15.5% acid detergent fiber and 19.9–29.1% neutral detergent fiber. They were enriched in phenolics (by up to 93.4%) and depleted in condensed tannin (by up to 59.3%) in comparison to the raw material. The thin stillages were used for cultivation of edible fungus Neurospora intermedia which produced 8.5–15.9 g L −1 ethanol and 4.8–16.2 g L −1 biomass containing over 62% protein. The mass balances showed that fermentation of unfiltered mashes was more efficient yielding up to 195.9 g kg −1 ethanol and 84.4% of protein recovery. [ABSTRACT FROM AUTHOR]

Dekkera bruxellensis hit the spotlight in the past decade mostly due to its rather high ability to adapt to several different fermentation processes. This yeast relies on different genetic and physiological aspects to achieve and preserve its high industrial fitness and some of these traits are shared with Saccharomyces cerevisiae. We have previously described that D. bruxellensis is unable to make use of accumulating trehalose as a strategy for cell adaptation and survival in the industrial scenario, as opposed to S. cerevisiae. Since trehalose is often involved in mechanisms related to cell protection, we aimed to investigate both cause and effect of the absence of this metabolite in the cell adaptive capacity in the industrial environment. Our results indicate that the major cause for the nonaccumulation of trehalose is the high constitutive activity of neutral trehalase. Therefore, the rate of trehalose degradation could be higher than its rate of synthesis, preventing accumulation. Altogether, our data elucidate the mechanisms involved in the lack of trehalose accumulation in D. bruxellensis as well as evaluates the implications of this feature. [ABSTRACT FROM AUTHOR]

Bioethanol is a renewable biofuel that has a strong inhibitory effect on cells in bioethanol fermentation by yeast. In this study, carbon nanotube (CNT)-mixed polydimethylsiloxane (PDMS) membranes were used for ethanol recovery from model solutions as well as for fermentation by self-flocculating yeast. Imbedding CNTs into the PDMS membrane led to enhanced ethanol recovery, with a maximum total flux of 128.7 g/m 2 h and an ethanol titer of 615.1 g/L in permeate. The CNTs can provide a flexible route for ethanol transport through the inner tubes or along the smooth surface. In fed-batch fermentation incorporating pervaporation, 112.3 g/L of ethanol was produced with an overall ethanol productivity and yield of 2.23 g/L h and 0.45 g/g, respectively. The membrane produced a highly concentrated condensate containing 400.3–487.5 g/L of ethanol. Furthermore, as yeast flocs can be throttled down in the bioreactor, self-flocculating yeast can be used to prevent membrane fouling induced by cell adsorption on the membrane. Therefore, the CNT-mixed membrane coupled with ethanol fermentation by self-flocculating yeast not only reduces ethanol-mediated inhibition of cells but also saves the production cost because of the reduced fouling risk. Thus, this combination approach has potential in industrial bioethanol production for long-time operation. [ABSTRACT FROM AUTHOR]

In this paper, genetic algorithm was used to investigate mathematical modeling of ethanol fermentation in a continuous conventional bioreactor (CCBR) and a continuous membrane bioreactor (CMBR) by ethanol permselective polydimethylsiloxane (PDMS) membrane. A lab scale CMBR with medium glucose concentration of 100 g L −1 and Saccharomyces cerevisiae microorganism was designed and fabricated. At dilution rate of 0.14 h −1 , maximum specific cell growth rate and productivity of 0.27 h −1 and 6.49 g L −1 h −1 were respectively found in CMBR. However, at very high dilution rate, the performance of CMBR was quite similar to conventional fermentation on account of insufficient incubation time. In both systems, genetic algorithm modeling of cell growth, ethanol production and glucose concentration were conducted based on Monod and Moser kinetic models during each retention time at unsteady condition. The results showed that Moser kinetic model was more satisfactory and desirable than Monod model. [ABSTRACT FROM AUTHOR]

Raw materials and pollution control are key issues for the ethanol fermentation industry. To address these concerns, food waste was selected as fermentation substrate, and stillage reflux was carried out in this study. Reflux was used seven times during fermentation. Corresponding ethanol and reducing sugar were detected. Accumulation of by-products, such as organic acid, sodium chloride, and glycerol, was investigated. Lactic acid was observed to accumulate up to 120 g/L, and sodium chloride reached 0.14 mol/L. Other by-products did not accumulate. The first five cycles of reflux increased ethanol concentration, which prolonged fermentation time. Further increases in reflux time negatively influenced ethanol fermentation. Single-factor analysis with lactic acid and sodium chloride demonstrated that both factors affected ethanol fermentation, but lactic acid induced more effects. [ABSTRACT FROM AUTHOR]

The effect of time and pressure on the selective extraction of sugar beet pectin using steam pre-treatment on unprocessed Sugar Beet Pulp was evaluated using a design of experiments approach. This process gave the highest solubilisation of pectin oligomers at a relatively low pressure and longer time (5 Bar, 24 min), whilst leaving the majority of the cellulose fraction intact. This method of steam pre-treatment fits into the concept of a sugar beet biorefinery as it valorises an existing waste stream without requiring any further physical processing such as milling or dilution with water. The residual cellulose fraction was enriched in cellulose and could be effectively fermented into ethanol by yeast after enzymatic digestion, producing 0.48 g ethanol per gram of glucose. [ABSTRACT FROM AUTHOR]

Hyper thermal (HT) acid hydrolysis of Kappaphycus alvarezii , a red seaweed, was optimized to 12% (w/v) seaweed slurry content, 180 mM H 2 SO 4 at 140 °C for 5 min. The maximum monosaccharide concentration of 38.3 g/L and 66.7% conversion from total fermentable monosaccharides of 57.6 g/L with 120 g dw/L K. alvarezii slurry were obtained from HT acid hydrolysis and enzymatic saccharification. HT acid hydrolysis at a severity factor of 0.78 efficiently converted the carbohydrates of seaweed to monosaccharides and produced a low concentration of inhibitory compounds. The levels of ethanol production by separate hydrolysis and fermentation with non-adapted and adapted Kluyveromyces marxianus to high concentration of galactose were 6.1 g/L with ethanol yield ( Y EtOH ) of 0.19 at 84 h and 16.0 g/L with Y EtOH of 0.42 at 72 h, respectively. Development of the HT acid hydrolysis process and adapted yeast could enhance the overall ethanol fermentation yields of K. alvarezii seaweed. [ABSTRACT FROM AUTHOR]

This paper reports on mild acid pretreatment options for the conversion of Agave tequilana leaves into composite sugars for ethanol fermentation. The effect of five different pretreatment conditions (time, temperature and acid concentrations) were assessed in terms of cellulose digestibility, hemicellulose solubilisation and lignin content in leaves of 1.25 years old A. tequilana plants from Rockhampton and 2.5 year plants from Kalamia. Dilute acid pretreatment and enzyme saccharification of A. tequilana leaf bagasse significantly improved total glucose recovery. A recovery of 273 mg/g (70% theoretical) was attained when the bagasse was pretreated with 2.0% H 2 SO 4 for 60 min at 121 °C and saccharified with 6% (w/w) CTec 2. Saccharomyces cerevisiae efficiently fermented crude A. tequilana bagasse and juice hydrolysates within 13 h and 7 h respectively, yielding up to 38.6 g/L and 12.4 g/L. This corresponds to glucose to ethanol conversion rate of 68 and 61% for A. tequilana leaf bagasse and juice, respectively. With further developments, including fermentation of C5 sugars and inulinase saccharification of juices (release of fructose), this process could deliver greater yields, reinforcing its potential as a biofuel feedstock. [ABSTRACT FROM AUTHOR]

Pretreatment with ozone combined with aqueous ammonia was used to recover residual organic carbon from recalcitrant solid digestate for ethanol production after anaerobic digestion (AD) of rice straw. Methane yield of AD at mesophilic and thermophilic conditions, and ethanol production of solid digestate were investigated. The results showed that the methane yield at thermophilic temperature was 72.2% higher than that at mesophilic temperature under the same conditions of 24 days and 17% solid concentration. And also the ethanol production efficiency of solid digestate after thermophilic process was 24.3% higher than that of solid digestate after mesophilic process. In this study, the optimal conditions for integrated methane and ethanol processes were determined as 55 °C, 17% solid concentration and 24 days. 58.6% of glucose conversion, 142.8 g/kg of methane yield and 65.2 g/kg of ethanol yield were achieved, and the highest net energy balance was calculated as 6416 kJ/kg. [ABSTRACT FROM AUTHOR]

Saccharomyces cerevisiae is the most widely used fermentation organism for ethanol production. However, the gene expression regulatory networks behind the ethanol fermentation are still not fully understood. Using a static fermentation model, we examined the ethanol yields on biomass of deletion mutants for 77 yeast genes encoding nonessential transcription factors, and found that deletion mutants for ACE2 and SWI5 showed dramatically increased ethanol yields. Overexpression of ACE2 or SWI5 in wild type cells reduced their ethanol yields. Furthermore, among the 34 target genes regulated by Ace2 and Swi5, deletion of CTS1, RPS4a, SIC1, EGT2, DSE2, or SCP160 led to increased ethanol yields, with the former two showing higher effects. Overexpression of CTS1 or RPS4a in both ace2/ace2 and swi5/swi5 mutants reduced their ethanol yields. In contrast, deletion of MCR1 or HO significantly decreased ethanol yields, with the former one showing the highest effect. Therefore, Ace2 and Swi5 are two negative regulators of ethanol yield during static fermentation of yeast cells, and both CTS1 and RPS4a are major effectors mediating these two transcription factors in regulating ethanol production. [ABSTRACT FROM AUTHOR]