Enhanced Bioethanol Production Research Articles

Analytical studies on carbohydrates of two cyanobacterial species for enhanced bioethanol production along with poly-β-hydroxybutyrate, C-phycocyanin, sodium copper chlorophyllin, and exopolysaccharides as co-products

In view of the world's immense dependency on non-renewable fossil fuels, the present study explores the prospect of Anabaena variabilis and Microcystis aeruginosa, which represent two distinct groups of cyanobacteria: nitrogen fixers and non fixers, for bioethanol production by analyzing the carbohydrate in their biomass, and maximizing its cellular accumulation inducing nitrate and phosphate stress. Under control condition, reducing sugar constituted 27.6% and 23.4% of the total carbohydrate, followed by glycogen exhibiting contents of 11.6% and 9.7% dry cell weight in the respective species. Cellulose, starch, and hemicellulose were obtained in lower quantities. Although phosphate starvation raised the carbohydrate content to a greater extent, its yield (mg L−1) was severely affected due to the depletion in the biomass. Hence, a biphasic phosphate-starved strategy was implemented generating a maximal carbohydrate content of 63.4% in A. variabilis and 55.1% in M. aeruginosa (compared to 46.2% and 41.4% under control) accompanied by ∼1.3-fold higher yield. Consequently, the bioethanol production in the test cyanobacteria reached 28.2% and 23.9% respectively with ∼1.3-fold higher (volumetric) yield than the control. Analysis of co-products revealed significant production of poly-β-hydroxybutyrate, C-phycocyanin, sodium copper chlorophyllin, and exopolysaccharides, wherein phosphate starvation induced effective stimulation of poly-β-hydroxybutyrate and exopolysaccharides, their yields again enhanced by respective ∼2 and ∼1.4-fold under the biphasic phosphate-starved approach. The present work stands out to be one of its kind comparing the suitability of A. variabilis and M. aeruginosa with an aim to have an overall view on cyanobacteria for bioethanol production by evaluating their carbohydrate profiles under different growth conditions, collectively with the production of various co-products, thus, supporting the bio-refinery concept.

Characterization of mechanical pulverization/phosphoric acid pretreatment of corn stover for enzymatic hydrolysis

Lignocellulosic biomass from corn stover holds promise as a raw material for the production of alternative energy to replace fossil fuels. In this study, structural properties of corn stover after pretreatment using mechanical pulverization with or without subsequent phosphoric acid treatment were investigated. The results showed that a pulverization step loosened the compact structure of corn stover lignocellulose and effectively reduced particle size, while both pulverization and phosphoric acid pretreatment steps altered the crystallinity index. During pretreatment, hemicellulose content was reduced and accessibility of β-1,4 glycosidic bonds to hydrolysis by cellulase increased, while almost all lignin was retained. The results showed that the combined two-step pretreatment method improved sugar yield from lignocellulose during subsequent enzymatic hydrolysis from 20.01 mg/g to 41.41 mg/g in glucose yield. These results should guide the development of methods for improved lignocellulose conversion to sugars for enhanced bioethanol production.

Co-expression of cellulase and xylanase genes in Saccharomyces cerevisiae toward enhanced bioethanol production from corn stover

ABSTRACT Lignocellulose is considered as a good resource for producing renewable energy. Previous in vitro studies have shown the synergistic action between cellulase and xylanase during lignocellulose biohydrolysis. In order to achieve the same effect in S. cerevisiae to enhance the practical biotransformation, two recombinant Saccharomyces cerevisiae strains (INVSc1-CBH-CA and INVSc1-CBH-TS) with co-expressed cellulase and xylanase were constructed. The cellulase and xylanase activities in INVSc1-CBH-CA and INVSc1-CBH-TS were 716.43 U/mL and 205.13 U/mL, 931.27 U/mL and 413.70 U/mL, respectively. The recombinant S. cerevisiae can use the partly delignified corn stover (PDCS) more efficiently and more ethanol producted than S. cerevisiae only expressing cellulase. Fermentation with INVSc1-CBH-CA and INVSc1-CBH-TS using PDCS ethanol yields increased by 1.7 and 2.1 folds higher than INVSc1-CBH, 2.8 and 3.4 folds higher than the wild type S. cerevisiae. The strategy of co-expression cellulase and xylanase in saccharomyces cerevisiae is effective and can be a foundation to research the mechanism of synergy effect of cellulose and xylanase.

Evaluation of Rice Bran as a Supplement for Production of Bioethanol by Saccharomyces cerevisiae

ABSTRACT There is an increase in researches to create alternative fuels through the use of biomass and agroindustrial lignocellulosic residues. The present study proposes the use of rice bran as source of energy with the potential to enhance bioethanol production. Using different concentrations of cells (1-5 g.L–1) and rice bran (2.5-7.5 g.L –1) with Saccharomyces cerevisiae, a factorial design 22 was carried out. The nutrient source provided by rice bran affects the substrate conversion in product (Yp/s) response in a quadratic form, but its linear form showed no significant effect (α = 0.05). When it comes to means, the best results were obtained for 12 h and for fermentation medium 2 (23.320 g.L–1 of ethanol), which contained the highest rice bran concentration and the lowest initial cell concentration. Medium 3, consisting of 2.5 g.L–1 and 5 g.L –1 of rice bran and cells, respectively, showed the lowest K s (4.434 g.L–1).

Fusarium oxysporum cultured with complex nitrogen sources can degrade agricultural residues: Evidence from analysis of secreted enzymes and intracellular proteome

Bioethanol production by using agricultural residues is an ecofriendly and renewable approach for energy production. Fusarium oxysporum URM 7401 produces an enzymatic arsenal that can be useful for biomass degradation and the cellulose saccharification. Thus, we aimed to identify in F. oxysporum URM 7401, cultured with 1% casein or feather meal in a submerged bioprocess, the intracellular protein profile in 2D gels, as well as evaluate the secreted enzymes in crude extracts and their capacity to degrade agricultural residues. Peptidase and xylanase production was higher with the use of feather meal than casein, whereas lipase production was increased upon culture with casein. Pectinase, β-glucosidase, filter paper-digesting activity, amylase and invertase was similar in both cultures. Intracellular analysis identified proteins involved in carbohydrate and protein metabolisms, energy generation and, notably, transaldolase a key enzyme for enhancing bioethanol production. The extract from the casein culture released reducing sugars from agricultural residues 2-fold more efficiently than did the extract from the feather-meal culture. Conversely, highest proteolytic activity in the feather-meal crude extract can account for the impaired sugar release measured. Our results emphasize the potential of using F. oxysporum URM 7401 for consolidated bioprocesses, due to the modulation of the cell metabolic machinery.

Extraction of ligninolytic enzymes from novel Klebsiella pneumoniae strains and its application in wastewater treatment

The presence of lignin and its derivatives in pulp effluent increases the pollution load on the environment. With an aim of better degradation and decolourization of wastewater, this study proposes the utilization of different ligninolytic enzymes from novel bacterial strains. Four novel bacterial strains of Klebsiellapneumoniae (K. pneumoniae strains NITW715076, NITW715076_1, NITW715076_2 and NITW715076_3) were isolated and identified. The ligninolytic enzymes were characterized by plate assay method. For the optimization of various process parameters of effluent sample, different approaches were used like one factor at a time and statistical optimization through response surface methodology (RSM). Further to validate the above data, enzyme activity, total phenolic concentration, GC–MS analysis and seed germination test were also performed. The ligninolytic enzymes produced were characterized as laccase and Manganese peroxidase (MnP). In lignin degradation and decolourization studies, consortia 1 (K. pneumoniae NITW715076_2 + K. pneumoniae NITW715076_1) (82.31%) was found more effective when compared to axenic culture (K. pneumoniae NITW715076_2) (74.1%). In RSM studies, Laccase and MnP activities were increased by 20% and 18%, respectively, as compared to one factor at a time optimization method. In addition, the enzyme activity for laccase and MnP after prediction by RSM was found 53338 IU/L and 147900 IU/L, respectively. The R2 values for both the enzymes were found to be significant. Further, GC–MS analysis also showed the degradation of different organic pollutants in effluent. Lastly, the seed germination test using consortia 1 corroborated the evidence of detoxification of industrial effluent. Effluent treated by consortia 1 showed better results in degradation and decolourization of lignin and their derivatives. Therefore, consortia 1 can be used for various industrial purposes like fruit juice clarification, diagnostic purposes and enhanced bioethanol production.

RSM based optimization of PEG assisted ionic liquid pretreatment of sugarcane bagasse for enhanced bioethanol production: Effect of process parameters

Production of bioethanol from lignocelluloses is highly dependent on pretreatment process. Therefore, a better understanding of this process is an essential prerequisite to consider the whole bioethanol production from lignocelluloses in a cost and energy efficient way. The first step in performing the pretreatment is to discover the effects of different process parameters on various chemical features of the lignocelluloses. In order to achieve this aim, response surface methodology (RSM) was chosen to assess the exact impact of variables including temperature, polyethylene glycol (PEG) concentration and time on glucan, xylan and acid insoluble lignin contents as responses, also to optimize the pretreatment process to finally achieve higher bioethanol production yields. 1-butyl-3-methylimidazolium chloride (BMIMCl) and PEG in the concentration range of 1–5 (%w/w) were used as pretreatment agents. Temperature and time levels of 100–160 °C and 60–120 min were considered for experimental design, respectively. For further understanding of the effects of pretreatment on lignocelluloses, structural features examined by FT-IR, SEM and XRD analysis, in addition, enzymatic hydrolysis and fermentation were implemented on the samples pretreated in optimum conditions. The optimum pretreatment condition is 154.6 °C, 60 min and 5 (%w/w) of PEG concentration which resulted to the high enzymatic conversion and bioethanol production.

Development of an environmental-benign process for efficient pretreatment and saccharification of Saccharum biomasses for bioethanol production

Abstract Saccharum biomasses (Saccharum munja and sugarcane bagasse) were subjected to different physical, chemical and biological pretreatment methods. Physical pretreatment of lignocellulosic biomasses was carried out by using steam treatment and microwave. Chemicals pretreament of lignocellulosic biomasses were optimized by using different chemicals like alkalies and acids. Among all chemicals, ammonia treatment significantly removed lignin (approx. 77%) and removed high amount of phenolic compounds and enhanced saccharification of Saccharum munja and sugarcane bagasse. Laccase pretreatment significantly removed lignin and enhanced the reducing sugar production by 2-fold corresponding to approx. 60% saccharification of pretreated biomass as compared to other methods. Fourier-transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) showed the removal of lignin due to pretreatments. Bio-ethanol production carried out using hydrolysate of both substrates by Saccharomyces cerevisiae and Pichia stipitis at 30 °C and 150 rpm after 72 h produced high amount of ethanol (25.06 g/L and 24.56 g/L for S. munja and sugarcane bagasse, respectively). Enzymatic hydrolysate fermented by the co-culture of S. cerevisiae and P. stipitis produced 30.78 g/L and 31.56 g/L of bioethanol from S. munja and sugarcane bagasse hydrolysate, respectively. Results indicated enhanced bioethanol production by co-culturing of pentose and hexose fermenting yeasts.

Effect of co-products of enzyme-assisted aqueous extraction of soybeans, enzymes, and surfactant on oil recovery from integrated corn-soy fermentation

Integrated corn-soy fermentation, utilizing co-products of soybean enzyme-assisted aqueous extraction process (EAEP) of soybeans in corn fermentation, has shown potential for enhancing bioethanol production compared to corn only fermentation. To maximize economic returns, oil may be recovered. In the present study, the effect of skim and insoluble fiber, and oil extraction aids on ethanol yield, oil partition, and oil recovery, and quality of Distillers Dried Grains (DDG) was investigated. Two fiber hydrolyzing enzymes (pectinase and cellulase), an acid protease (Fermgen®), and a surfactant (Tween 80) were evaluated. Addition of skim, mixture of skim and insoluble fiber, or Fermgen® to corn fermentation resulted in a ∼32 h decrease in fermentation time. Addition of soy co-products also resulted in ∼10–28% increase in oil partition in thin stillage with no additional enzyme or surfactant treatment. Addition of insoluble fiber alone resulted in ∼19% decrease in solids partition in thin stillage. Maximum free oil recovery, 22.5 ± 4.5%, was achieved from corn-insoluble fiber thin stillage with a combined treatment of enzymes (pectinase, cellulase, and Fermgen®) and surfactant (Tween 80). Maximum extractable oil recovery, 67 ± 3.2%, was achieved with the enzyme treatment alone. Corn-soy DDG has ∼11% higher protein, ∼2% lower fiber, and ∼2% lower fat contents compared to corn DDG. The fiber content was further reduced to ∼2% after enzyme treatment. This study demonstrates an efficient use of soy EAEP co-products and enzymes to maximize oil partition in thin stillage, and produce a high quality corn-soy DDG.

Enhanced Bioethanol Production from Potato Peel Waste Via Consolidated Bioprocessing with Statistically Optimized Medium.

In this study, an extensive screening was undertaken to isolate some amylolytic microorganisms capable of producing bioethanol from starchy biomass through Consolidated Bioprocessing (CBP). A total of 28 amylolytic microorganisms were isolated, from which 5 isolates were selected based on high α-amylase and glucoamylase activities and identified as Candida wangnamkhiaoensis, Hyphopichia pseudoburtonii (2 isolates), Wickerhamia sp., and Streptomyces drozdowiczii based on 26S rDNA and 16S rDNA sequencing. Wickerhamia sp. showed the highest ethanol production (30.4g/L) with fermentation yield of 0.3g ethanol/g starch. Then, a low cost starchy waste, potato peel waste (PPW) was used as a carbon source to produce ethanol by Wickerhamia sp. Finally, in order to obtain maximum ethanol production from PPW, a fermentation medium was statistically designed. The effect of various medium ingredients was evaluated initially by Plackett-Burman design (PBD), where malt extracts, tryptone, and KH2PO4 showed significantly positive effect (p value <0.05). Using Response Surface Modeling (RSM), 40g/L (dry basis) PPW and 25g/L malt extract were found optimum and yielded 21.7g/L ethanol. This study strongly suggests Wickerhamia sp. as a promising candidate for bioethanol production from starchy biomass, in particular, PPW through CBP.

Composite Multi Wall Carbon Nano Tube Polydimethylsiloxane Membrane Bioreactor for Enhanced Bioethanol Production from Broomcorn Seeds

Broomcorn seed (Sorghum vulgare) was used as raw material for bioethanol production. Optimum conditions were obtained from response surface method. Broomcorn seed flour (45 g/l) was treated by alkaline treatment and dual enzymatic hydrolysis (0.7 g/l of α- amylase and 0.42 g/l of amyloglucosidase). The hydrolyzed total sugar of 25.5 g/L was used in conventional bioethanol production (8.1 g/l) using Saccharomyces cerevisiae. Enhanced bioethanol production was performed in membrane bioreactor (MBR) in integrated batch fermentation and membrane pervaporation process. Application of commercial polydimethylsiloxane/polyethyleneterephthalate/polyimide (PDMS/PET/PI) membrane in MBR resulted in ethanol concentration of 10.15 g/l in broth and 70.2 g/l in cold trap of MBR. Cell concentration in broth was increased from 7.2 in conventional fermentation to 9.05 g/l in MBR. In addition, ethanol production in MBR using fabricated membrane having ethanol separation factor of 8.7; ethanol concentration in broth and cold trap were 11.1 and 88.5 g/ l, respectively. Also the cell concentration of 10.2 g/l was obtained in MBR with fabricated membrane. In MBR, surface modified multi wall carbon nano tube (MWCNT) coated on membrane having ethanol separation factor of 10.2, resulted ethanol concentration of 11.9 and 110 g/l in broth and cold trap, respectively. Finally, for MBR using modified membrane the cell concentration of 11.01 g/l was obtained. Based on a comparison study, maximum ethanol separation and yield were obtained for modified membrane having MWCNT and the surface was modified by corona treatment.

Bioethanol a Microbial Biofuel Metabolite; New Insights of Yeasts Metabolic Engineering

Scarcity of the non-renewable energy sources, global warming, environmental pollution, and raising the cost of petroleum are the motive for the development of renewable, eco-friendly fuels production with low costs. Bioethanol production is one of the promising materials that can subrogate the petroleum oil, and it is considered recently as a clean liquid fuel or a neutral carbon. Diverse microorganisms such as yeasts and bacteria are able to produce bioethanol on a large scale, which can satisfy our daily needs with cheap and applicable methods. Saccharomyces cerevisiae and Pichia stipitis are two of the pioneer yeasts in ethanol production due to their abilities to produce a high amount of ethanol. The recent focus is directed towards lignocellulosic biomass that contains 30–50% cellulose and 20–40% hemicellulose, and can be transformed into glucose and fundamentally xylose after enzymatic hydrolysis. For this purpose, a number of various approaches have been used to engineer different pathways for improving the bioethanol production with simultaneous fermentation of pentose and hexoses sugars in the yeasts. These approaches include metabolic and flux analysis, modeling and expression analysis, followed by targeted deletions or the overexpression of key genes. In this review, we highlight and discuss the current status of yeasts genetic engineering for enhancing bioethanol production, and the conditions that influence bioethanol production.

Largely enhanced bioethanol production through the combined use of lignin-modified sugarcane and xylose fermenting yeast strain

The recalcitrant structure of lignocellulosic biomass is a major barrier in efficient biomass-to-ethanol bioconversion processes. The combination of feedstock engineering via modification in the lignin synthesis pathway of sugarcane and co-fermentation of xylose and glucose with a recombinant xylose utilizing yeast strain produced 148% more ethanol compared to that of the wild type biomass and control strain. The lignin reduced biomass led to a substantially increased release of fermentable sugars (glucose and xylose). The engineered yeast strain efficiently co-utilized glucose and xylose for fermentation, elevating ethanol yields. In this study, it was experimentally demonstrated that the combined efforts of engineering both feedstock and microorganisms largely enhances the bioconversion of lignocellulosic feedstock to bioethanol. This strategy will significantly improve the economic feasibility of lignocellulosic biofuels production.

Enhancing bioethanol production from water hyacinth by new combined pretreatment methods

This study investigated the possibility of enhancing bioethanol production by combined pretreatment methods for water hyacinth. Three different kinds of pretreatment methods, including microbial pretreatment, microbial combined dilute acid pretreatment, and microbial combined dilute alkaline pretreatment, were investigated for water hyacinth degradation. The results showed that microbial combined dilute acid pretreatment is the most effective method, resulting in the highest cellulose content (39.4 ± 2.8%) and reducing sugars production (430.66 mg·g−1). Scanning Electron Microscopy and Fourier Transform Infrared Spectrometer analysis indicated that the basic tissue of water hyacinth was significantly destroyed. Compared to the other previously reported pretreatment methods for water hyacinth, which did not append additional cellulase and microbes for hydrolysis process, the microbial combined dilute acid pretreatment of our research could achieve the highest reducing sugars. Moreover, the production of bioethanol could achieve 1.40 g·L−1 after fermentation, which could provide an extremely promising way for utilization of water hyacinth.

Characterisation of sweet stem sorghum genotypes for bio-ethanol production

ABSTRACTIn an effort to characterise and select promising sweet stem sorghum genotypes with enhanced biofuel productivity, the present study investigated phenotypic variability present among diverse sweet stem sorghum genotypes based on ethanol production and related agronomic traits. One hundred and ninety genotypes were evaluated. Data were subjected to variance, cluster, correlation, path coefficient and principal component analyses. Significant differences (P < 0.01) were detected among tested genotypes for all measured traits. Days to flowering varied from 62 to 152 with a mean of 93. Plant height varied from 90 to 420 cm with a mean of 236 cm. Stem diameter ranged from 7 to 31 mm with a mean of 16 mm. Biomass yield varied from 6.668 to 111.2 t ha−1 with a mean of 30 t ha−1. Stalk dry matter content ranged from 17.2% to 44.2% with a mean of 29.8%, while fibre content varied from 8.92% to 34.8% with a mean of 17.2%. The stalk brix yield varied from 3.3% to 18.9% with a mean of 12.1%. Ethanol productivity ranged from 240.9 to 5500 l ha−1 with a mean of 1886 l ha−1. The best ethanol producing genotypes were AS203, AS391, AS205, AS251 and AS448. Days to flowering, plant height, stalk brix and stem diameter exerted the greatest indirect effects on ethanol production through higher biomass production. Biomass yield had the greatest direct effect on ethanol production. Therefore, the above traits should be considered during breeding sorghum for bio-ethanol production. Also, the traits had high heritability values, hence selection should provide for good genetic gains. Overall, the above sweet stem sorghum genotypes are useful genetic resources for breeding of sorghum with enhanced bio-ethanol production.

Studies on enhanced bio-ethanol production by fermentation using yeast cells

Studies on enhanced bio-ethanol production by fermentation using yeast cells

Enhanced Bio-ethanol Production from Old Newspapers Waste Through Alkali and Enzymatic Delignification

Producing bioethanol from various lignocellulosic wastes is considered as a promising strategy to overcome global energy crisis and waste management in one consolidated step. In this study, we investigated the use of old newspaper waste as potential raw materials for bioethanol production. Two state-of-the-art technologies, alkali (NaOH) and enzymatic (ligninolytic) pre-treatments were applied for the delignification of old newspaper waste. The maximum delignification of 37.7 and 42.2% were achieved with alkali (4.0% after 24 h) and ligninolytic extract (25 mL) treatments, respectively. The delignified residues were then treated with cellulase extract from Trichoderma harzianum that resulted in 56.2 and 63.8% cellulose hydrolysis in alkali and enzyme treated substrates, respectively. The enzymatically digested hydrolyzates were submitted for fermentation anaerobically, and up to 11.95 and 12.69 g/L ethanol concentration was recorded, respectively. Effects of several processing parameters such as fermentation duration, substrate level, pH, temperature, and inoculum volumes were optimized that led to significantly higher ethanol production of 17.8 and 20.4 g/L for alkali and enzyme treated substrates, respectively. The results obtained suggested that ligninolytic pre-treatment is a more efficient and environmentally friendlier approach as compared to alkali treatment for economic bio-ethanol production.

Enhanced bioethanol production by fed-batch simultaneous saccharification and co-fermentation at high solid loading of Fenton reaction and sodium hydroxide sequentially pretreated sugarcane bagasse

A study on the fed-batch simultaneous saccharification and co-fermentation (SSCF) of Fenton reaction combined with NaOH pretreated sugarcane bagasse (SCB) at a high solid loading of 10–30% (w/v) was investigated. Enzyme feeding mode, substrate feeding mode and combination of both were compared with the batch mode under respective solid loadings. Ethanol concentrations of above 80g/L were obtained in batch and enzyme feeding modes at a solid loading of 30% (w/v). Enzyme feeding mode was found to increase ethanol productivity and reduce enzyme loading to a value of 1.23g/L/h and 9FPU/g substrate, respectively. The present study provides an economically feasible process for high concentration bioethanol production.

Bioethanol production from individual and mixed agricultural biomass residues

Cellulosic bioethanol production has been fraught with challenges, including fluctuations in feedstock supply, handling costs, pretreatment, enzymes, and other logistical problems. Most studies of lignocellulosic ethanol production have focused on a single type of biomass; however, full utilization of various lignocellulosic biomass sources might enhance bioethanol production and the economic feasibility of the biorefinery. The goal of this study was to evaluate the effectiveness of popping pretreatment on saccharification and fermentation for individual and mixed biomass. We then compared separate hydrolysis and fermentation (SHF) with simultaneous saccharification and fermentation (SSF) processing, with the aim of optimizing production of bioethanol from biomass. Saccharification efficiencies were increased significantly in all the popping-pretreated compared to the non-pretreated individual and mixed biomass. The SSF was superior compared to SHF processing. Our results indicated that the saccharification efficiencies of both individual and mixed biomass were improved after popping pretreatment; in particular, the production of bioethanol from mixed biomass was identified as a suitable approach for more extensive application.

Addition of expansin to cellulase enhanced bioethanol production

Abstract A metagenomic clone (pUC-189) that exhibited clear zone on CMC agar plate showed homology with glycosyl hydrolase (GH) family 12 endoglucanase. Purified recombinant cellulase (C18) exhibited the highest activity towards CMC followed by Avicel PH101 and waste paper which was confirmed by chromatography. Role of expansin (E11CB) was investigated to address the poor activity of C18 towards waste paper. The Langmuir isotherm for binding of the purified E11CB to waste paper showed a good fit (R 2 = 0.97). Recombinant E11CB protein bound to waste paper was detected in situ by UV fluorescence of [Ln(DPA) 3 ] 3− complex. Scanning electron microscopy confirmed that binding of E11CB transformed smooth microfibrils into rough and amorphic surface. Improvement in the enzymatic hydrolysis of pure cellulose and lignocelluloses was observed after treatment with purified E11CB at low cellulase loading. The enzymatic hydrolysate of waste cellulose paper was then used as the substrate for bioethanol production by Saccharomyces cerevisiae.