Highest Ethanol Yield Research Articles

Higher thermal and ethanol tolerance of a yeast strain isolated from oral cavity

Efficient bioethanol producing microorganisms must be endowed with peculiar physiological and technological traits, such as, higher thermal and ethanol tolerance. This encompasses a strain thermotolerance and an ability to grow at elevated sugar and ethanol concentration or ability to sustain dehydration process such as freeze drying. In this study, we characterized a thermotolerant yeast strain isolated from the human oral cavity regarding the above mentioned parameters. Such an uncommon niche was considered as the great potential reservoir, to isolate strains endowed with metabolic aptitudes requested for ethanol production. In the process, we have defined the YTerm-1strain ability to sustain high sugar and ethanol concentration that are two technological constrains in bioethanol production. Finally, we highlighted that the strain YTerm-1 was able to accumulate, at a high level, trehalose and β-glucan, two compounds conferring the cells an increased resistance to freeze drying process and osmotic stress. Our results suggest that the Yterm-1 strain showed a better growth ability and higher ethanol yield as compared to the industrial strain. Other metabolic traits, such as resistance to dehydration stress, tolerance to ethanol, accumulation of intracellular trehalose or membrane β-glucan confer to that isolate all the characteristics requested in industrial production of ethanol.

Fungal oxidoreductases and CAZymes effectively degrade lignocellulosic component of switchgrass for bioethanol production

• Fungal oxidoreductases and CAZymes were produced in a bioreactor. • Laccase isozymes removed lignin up to 33.9 % from switchgrass. • Microscopic and spectroscopic analysis clearly indicated lignin degradation. • Laccase treatment improved 22.47 fold sugar hydrolysis over untreated biomass. • Fermentation studies showed high ethanol yield (78.32 % of theoretical yield). Ganoderma lucidum , a basidiomycetous fungus, has enormous potential in the co-production of diverse extracellular oxidoreductases and CAZymes. In the present study, G. lucidum MDU-7 produced 510 U/ml of laccases, xylanase (3.0 IU/ml) and cellulase (3.1 FPU/ml) in a lab-scale bioreactor. Laccase pretreatment of switchgrass in a laboratory-designed bioreactor resulted in better phenol degradation (64.27 %), lignin removal (33.9 %), and increase in cellulose crystallinity (12.66 %). The pretreatment efficacy was validated using various microscopic and spectroscopic techniques (SEM, FTIR, and XRD). The hydrolysis of laccase pretreated biomass using diverse cellulases from Aspergillus oryzae MDU-4, Aspergillus flavus MDU-5, Trichoderma citrinoviride MDU-1, and Trichoderma longibrachiatum MDU-6 resulted in 162.7 mg/g, 120.4 mg/g, 157.3 mg/g, and 176.25 mg/g release of sugars, respectively. The enzymatic hydrolysates containing 3.37–5.11 g/L sugars were fermented by Saccharomyces cerevisiae NCIM-3640 strain which resulted into 1.32–1.96 g/L ethanol, with high production yield (31.42–39.16 %). Our findings suggest that laccase pretreatment technology may provide a promising and environmentally benign alternative for the sustainable development of lignocellulosic biorefinery.

An engineered non-oxidative glycolytic bypass based on Calvin-cycle enzymes enables anaerobic co-fermentation of glucose and sorbitol by Saccharomyces cerevisiae

BackgroundSaccharomyces cerevisiae is intensively used for industrial ethanol production. Its native fermentation pathway enables a maximum product yield of 2 mol of ethanol per mole of glucose. Based on conservation laws, supply of additional electrons could support even higher ethanol yields. However, this option is disallowed by the configuration of the native yeast metabolic network. To explore metabolic engineering strategies for eliminating this constraint, we studied alcoholic fermentation of sorbitol. Sorbitol cannot be fermented anaerobically by S. cerevisiae because its oxidation to pyruvate via glycolysis yields one more NADH than conversion of glucose. To enable re-oxidation of this additional NADH by alcoholic fermentation, sorbitol metabolism was studied in S. cerevisiae strains that functionally express heterologous genes for ribulose-1,5-bisphosphate carboxylase (RuBisCO) and phosphoribulokinase (PRK). Together with the yeast non-oxidative pentose-phosphate pathway, these Calvin-cycle enzymes enable a bypass of the oxidative reaction in yeast glycolysis.ResultsConsistent with earlier reports, overproduction of the native sorbitol transporter Hxt15 and the NAD+-dependent sorbitol dehydrogenase Sor2 enabled aerobic, but not anaerobic growth of S. cerevisiae on sorbitol. In anaerobic, slow-growing chemostat cultures on glucose–sorbitol mixtures, functional expression of PRK-RuBisCO pathway genes enabled a 12-fold higher rate of sorbitol co-consumption than observed in a sorbitol-consuming reference strain. Consistent with the high Km for CO2 of the bacterial RuBisCO that was introduced in the engineered yeast strains, sorbitol consumption and increased ethanol formation depended on enrichment of the inlet gas with CO2. Prolonged chemostat cultivation on glucose–sorbitol mixtures led to loss of sorbitol co-fermentation. Whole-genome resequencing after prolonged cultivation suggested a trade-off between glucose-utilization and efficient fermentation of sorbitol via the PRK-RuBisCO pathway.ConclusionsCombination of the native sorbitol assimilation pathway of S. cerevisiae and an engineered PRK-RuBisCO pathway enabled RuBisCO-dependent, anaerobic co-fermentation of sorbitol and glucose. This study demonstrates the potential for increasing the flexibility of redox-cofactor metabolism in anaerobic S. cerevisiae cultures and, thereby, to extend substrate range and improve product yields in anaerobic yeast-based processes by enabling entry of additional electrons.

Bioethanol Production Potential and Other Biomass Energy Properties of Invasive Reynoutria, Solidago, and Spiraea Plants

Due to the threat posed by the spread of invasive plant species, there is an urgent need to develop effective methods of eradicating and managing their biomass. The aim of the study was to examine selected invasive plants in terms of their use for energy purposes and to find out whether they can be a raw material for the production of second-generation biofuels. First, their chemical compositions were determined. The higher heating value (HHV) and lower heating value (LHV) were also calculated. High values of the higher heating value, ranging from 18.490 MJ∙kg−1 to 19.900 MJ∙kg−1, indicate the possibility of using the biomass of invasive plants for energy purposes (combustion). All investigated invasive plant species were also subjected to the process of obtaining ethanol. This included an alkaline pretreatment with 1% sodium hydroxide, followed by a simultaneous saccharification and fermentation (SSF) process. The highest ethanol yield per ha of plants was obtained at 2.6 m3∙ha−1 for the Reynoutria × bohemica biomass. The remaining species showed an ethanol yield below 2 m3∙ha−1. The conducted research allows for the conclusion that the studied invasive plants can be a promising raw material for the production of bioethanol.

Combining ability studies through Line × Tester design in sweet sorghum (Sorghum bicolor L.) for bioethanol production

In developing of sweet sorghum hybrids, non-additive genetic effects are important in phenotypic expression of the traits of interest. The present experiment was undertaken to assess the combining ability in sweet sorghum genotypes using 16 hybrids developed by crossing four CMS lines with four elite testers in a Line × Tester mating design. The hybrids were evaluated at three locations in  Andhra Pradesh in a Randomized Block Design with two replications during Rabi, 2018. Among the 13 quantitative characters studied the non-additive genetic variance was higher than the additive variance for all the traits except for days to 50 % flowering, days to maturity, plant height and ethanol yield. Among parents, ICSA 14029, ICSA 14030 (females) ICSV 15006 and GGUB-28 (males) were found to be  good general combiners for ethanol yield and its related traits with consistent performance across locations. ICSA 14029 × ICSV-15006 and ICSA 14033 × SEVS-08 were identified as superior crosses for the specific combining ability for high ethanol yield. Keywords: Sweet sorghum, Brix %, Bioethanol, gca, sca components

Chemocatalytic Conversion of Lignocellulosic Biomass to Ethanol: A Mini-Review

Ethanol has been widely used as a clean fuel, solvent, and hydrogen carrier. Currently, ethanol is generally produced through fermentation of starch- and sugarcane-derived sugars (e.g., glucose and sucrose) or ethylene hydration. Its production from abundant and inexpensive lignocellulosic biomass would facilitate the development of green and sustainable society. Biomass-derived carbohydrates and syngas can serve as important feedstocks for ethanol synthesis via biological and chemical pathways. Nevertheless, the biological pathway for producing ethanol through biomass-derived glucose fermentation has the disadvantages of long production period and carbon loss. These issues can be effectively mitigated by chemocatalytic methods, which can readily convert biomass to ethanol in high yields and high atomic efficiency. In this article, we review the recent advances in chemocatalytic conversion of lignocellulosic biomass to ethanol, with a focus on analyzing the mechanism of chemocatalytic pathways and discussing the issues related to these methods. We hope this mini-review can provide new insights into the development of direct ethanol synthesis from renewable lignocellulosic biomass.

Target and Enhance Ethanol and Butyrate Production from Anaerobic Fermentation via the pH and Organic Loading Rate Combined Strategy.

The large capacity production and low utilization rate increase the difficulty of fruit and vegetable wastes (FVW) treatment. Efficient and targeted recovery strategies can solve these problems. This study investigated and proposed combined strategies via pH and organic loading rate (OLR) to target and enhance ethanol- and butyrate-dominant acidogenic production in the FVW mixed culture fermentation. Under pH 4.0, OLR 18 gCOD/(L∙d), and mesophilic (35°C), ethanol-dominant fermentation was formed. The long-term operation (168days) showed that the highest ethanol yield was 0.33g/gCOD which was greater than that in other studies. Also, the hydrolysis rate of ethanol-type fermentation reached 74.5%. Besides, butyrate-type fermentation was stable at yield 0.39g/gCOD following conditions: pH 6.0, OLR 28 gCOD/(L∙d), and 35°C, of which hydrolysis and acidogenic rate were 78.0% and 62.0%, respectively. The high relative abundance of Lactobacillus, Olsenella, and Bifidobacterium played positive role in achieving ethanol, butyrate, and lactate production among various metabolic pathways. The results revealed the pH value together with OLR was the valid parameter to affect product formation and composition during FVW fermentation.

Exploratory Studies on the Technical Viability of Bioethanol Production from Fermented Sago (Metroxylon sagu) Starch

This study was conducted to assess the viability of production of bioethanol from Metroxylon sagu Rottb. The experimental setup included different levels of yeast and molasses in the substrate. There were nine treatments examined in this experiment. The YIM1 (50g yeast, 150g molasses), Y2M1 (100g yeast, 150g molasses), Y3M1 (150g yeast, 150g molasses), Y1M2 (50g yeast, 200g of molasses), Y2M2 (100g yeast, 200g molasses), Y3M2 (150g yeast, 200g molasses), Y1M3 (50g yeast, 250g molasses), Y2M3 (100g yeast, 250g molasses), Y3M3 (150g yeast, 250g molasses). Experiment was monitored by their brix, temperature and time of fermentation. The results shows that higher the brix measured, has high yield of ethanol produced, among the treatments Y2M3 (100g yeast, 250g of molasses) gained higher yield of ethanol with 40.33% produced during first distillation. On the other hand, the lowest yield was Y3M1 (150g yeast, 150g molasses) with 17% gained of distillate from the mixture and has longer fermentation period. Using Analysis of Variance, RCBD, the level of significance was determined.

Statistical optimization of cellulase production and its efficacy in hesperidin extraction from orange peel and bioethanol production from rice straw by simultaneous saccharification and fermentation

Cellulolytic enzymes are of great interest for the hydrolysis of cellulosic biomass and their demand is increasing intensely due to their potential applications in second generation bioethanol production. In this study, cellulase production from Bacillus cereus KG10 was explored and the production media and cultural conditions were optimized through Box-Behnken design. Under optimized conditions, the cellulase activity was improved to 0.51 U/mL. The purity and the molecular mass of the enzyme (55.1 kDa) were confirmed by HPLC and MOLDI-TOF MS respectively. Additionally, cellulase mediated extraction of hesperidin was performed to prove extraction efficiency by ESI-MS. Likewise, the cellulase efficiency in bioconversion of lignocellulosic biomass was also confirmed towards improving the ethanol yield. The results showed that higher amounts of reducing sugar 73.2 and 89.3 % were explored from cellulase mediated hydrolysis of rice straw than that from acidalkali mediated hydrolysis. A high ethanol yield was also achieved in media added with cellulase treated rice straw (38.1 g/L) than that of acid-alkali treated rice straw (27.4 g/L) through simultaneous saccharification and fermentation (SSF) process using cellulase from B. subtilis KG10 and Saccharomyces cerevisiae. Thus, the cellulase from B. cereus KG10 could be a potential candidate in various industrial sectors.

Bioethanol production from expired cookies and economic analysis for practical application

This work examined the potential of bioethanol production from expired cookies (EC) by the separate hydrolysis and fermentation process. EC was hydrolyzed by glucoamylase with different enzyme addition (3.5 U/g to 140 U/g) to produce the EC hydrolysate. The glucose concentration increased with enzyme addition from 3.5 U/g to 14 U/g and the highest glucose concentration of 21.2 g/L was obtained. The EC hydrolysate was used by Saccharomyces cerevisiae for bioethanol production. The optimal ethanol production obtained from this study was 40.1 g/L in term of economics and efficiency. According to the mass balance, the highest ethanol yield from EC was 0.4 g/g. Techno-economic analysis of the plant with capacity of 5 tons EC/day was also assessed in this study. The total capital cost and annual operation cost were US$540400.7 and US$144543.9/y, respectively. The revenue of the plant was US$390522/y with the sales of 660 t/y ethanol and 412.5 t/y oils. The plant should feed the EC more than 1.04 t/d (334.2 t/y) to avoid the shutdown point. This is the first study to demonstrate the bioethanol production from EC and assess the economic feasibility for industrial application.

Dilute Sulphuric Acid Pre-treatment for Efficient Production of Bioethanol from Sugarcane Bagasse using Saccharomyces cerevisiae

In the present study, the effect of dilute acid hydrolysis during the pre-treatment of sugarcane bagasse (SCB) was conducted using sulphuric acid of various concentrations. A high concentration of reducing sugar of 270.90 g/L was achieved by soaking bagasse in 0.5M of H2SO4 at a constant temperature of 120 oC. After the pre-treatment (saccharification), the reducing sugars obtained at the different concentrations were fermented by Saccharomyces cerevisiae mono-culture modes. The results indicated that, the pre-treated SCB treated with 0.5M H2SO4 produced the highest yield of ethanol which was 8.884 g/L with a productivity of 0.134 g/L/h. However, relatively low ethanol yield was found when 0.2M H2SO4 was used which yielded 8.2185 g/L. In any case, acid hydrolysis proves to be a better method of hydrolysis and an increase in the concentration during hydrolysis contributes to higher sugar yield and subsequently higher ethanol yields.

Optimization of a 10 Litre Full Electric Reflux Distiller

Sugar sap from Nipa (Nypa fruiticans) palm is one of the promising sustainable feedstocks for ethanol production. There are different stages and processes needed for the sap to produce ethanol particularly: collection, fermentation, and distillation. In order to produce high ethanol concentration and yield, each stage or process needs to be optimized and improved as such, this study optimized the flow rate and temperature of the cooling system of a 10 L full electric Reflux distiller for the production of a fuel grade (95%) bioethanol from nipa sap. The optimal power density for the 10 L full electric reflux distiller was also determined. Optimizing these parameters improved the concentration of the ethanol, ethanol yield and also decreased the operational cost of the 10 L full electric reflux distiller. First step was to determine the power density required for the 10 L Lab-Scale Distiller through experiment using different power density. After identifying the power density, multiple trials were performed with 2 protocols being the continuous method and recirculating method of the cooling system. Results showed that a flow rate of 0.77 L/min, a 27 °C cooling liquid temperature and a 100W/m3 power density were obtained. An increase of 154.2% in volume of consistent 95% concentration yield was observed. Also, there was a significant increase in the yield. Continuous method was faster by an average of 26 minutes compared to the recirculating method.

Water and Green Energy as the Heart of Sustainable Development – Promoting Sustainable Environment Through Innovate Engineering Technology in Nigeria Economy

Water for energy, energy for water is an independent sector and through their inextricable linkage, water and energy remains the key driver of economic growth and social development. The benefits water and energy (W-E) provides are: on poverty reductions, economic progress-impairment on the ecosystems, but has quantified costs. In addition, it improves the health and in education, promotes stable society and human dignity and help in realizing basic human rights. When achieving developmental goals on W-E sustainability, it is of disadvantages that there will be an increase on water scarcity, high exposure to environmental degradation, e.g. floods and droughts etc., scaling energy prices which will reduce on access to W-E and in-turn increase poverty and by extension impact on natural ecosystems. By improving the performance optimization on W-E nexus; the resultant increase on energy efficiency; decrease water pollution, reduce costs of energy and water provision, increase access to services and reduce greenhouse gas (GHG) emission. The effective development of renewable energy worldwide would be a stabilizing driver on fossil fuel availability and global climate change. Water is especially important and used in large volumes in generating electricity, whether through green energy (hydroelectric power), or heat exchange (steam systems), and for cooling (nuclear). This paper presents some studies on algae formations instead of traditional agro-based raw materials, because it does not compete with food or fodder and is abundantly available in fresh water or marine ecosystem. The studies show that algal species can be used to produce biodiesel (biofuels). A comparative study was conducted using chemically pre-treated with NaOH and un-treated spirogyra biomass. The spirogyra biomass was subjected to saccharification process by the fungi Aspergillus Niger for hydrolysis, for six (6) days and then followed by the fermentation process by using yeast (Saccharomyces cerevisiae) for another 6 days. The comparative study experimented, and the results recorded showed that high yield of ethanol was obtained for un-treated Spirogyra biomass when compared to chemically pre-treated biomass. Additional studies reveal that inducement of fertilizer and other growth media can be used to increase the growth rate of biofuels production from algae. Oil produced from algae was esterified using CH3OH as catalyst. The properties of the biodiesel produced clearly show that biodiesel produced from green algae can be used to run engine. The experimental results show that the Flash point was 1350C, Pour point was 170C and Cloud point was 180C and are all in agreement with the standard of biodiesel (biofuels). The current production cost of bioethanol plant is $26,560 US. Keywords: Energy, water, environment, and sustainability

Engineering proton-coupled hexose uptake in Saccharomyces cerevisiae for improved ethanol yield.

BackgroundIn the yeast Saccharomyces cerevisiae, which is widely applied for industrial bioethanol production, uptake of hexoses is mediated by transporters with a facilitated diffusion mechanism. In anaerobic cultures, a higher ethanol yield can be achieved when transport of hexoses is proton-coupled, because of the lower net ATP yield of sugar dissimilation. In this study, the facilitated diffusion transport system for hexose sugars of S. cerevisiae was replaced by hexose–proton symport.ResultsIntroduction of heterologous glucose– or fructose–proton symporters in an hxt0 yeast background strain (derived from CEN.PK2-1C) restored growth on the corresponding sugar under aerobic conditions. After applying an evolutionary engineering strategy to enable anaerobic growth, the hexose–proton symporter-expressing strains were grown in anaerobic, hexose-limited chemostats on synthetic defined medium, which showed that the biomass yield of the resulting strains was decreased by 44.0-47.6%, whereas the ethanol yield had increased by up to 17.2% (from 1.51 to 1.77 mol mol hexose−1) compared to an isogenic strain expressing the hexose uniporter HXT5. To apply this strategy to increase the ethanol yield on sucrose, we constructed a platform strain in which all genes encoding hexose transporters, disaccharide transporters and disaccharide hydrolases were deleted, after which a combination of a glucose–proton symporter, fructose–proton symporter and extracellular invertase (SUC2) were introduced. After evolution, the resulting strain exhibited a 16.6% increased anaerobic ethanol yield (from 1.51 to 1.76 mol mol hexose equivalent−1) and 46.6% decreased biomass yield on sucrose.ConclusionsThis study provides a proof-of-concept for the replacement of the endogenous hexose transporters of S. cerevisiae by hexose-proton symport, and the concomitant decrease in ATP yield, to greatly improve the anaerobic yield of ethanol on sugar. Moreover, the sugar-negative platform strain constructed in this study acts as a valuable starting point for future studies on sugar transport or development of cell factories requiring specific sugar transport mechanisms.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13068-022-02145-7.

A comparative study between ionic liquid and acidic pretreatment of waste cotton textiles with simultaneous saccharification and fermentation

Millions of tons of waste cotton textiles are discarded every year while they could have been used for the production of bioethanol as an alternative for fossil fuel. In this study, the potential of cotton as raw material for ethanol production using ionic liquid (IL) pretreatment and acidic pretreatment is examined and compared, along with non-pretreated cotton samples. The study also aims to determine the optimal temperature of ionic liquid pretreatment, for which experiments under three temperatures (95°C, 150°C, and 175°C) were carried out. Subsequently, the pretreated cotton samples were converted to bioethanol via simultaneous saccharification and fermentation (SSF). Ethanol yields resulting from different pretreatment methods (also non-pretreatment) were compared. Findings suggest that ionic liquid pretreatment under 175°C gives the highest ethanol yield, proving it to be a competitive alternative to traditional acid pretreatment widely applied in industry, as well as demonstrating the prospective usage of waste cotton textiles as biomass for the production of renewable biofuel. Bangladesh J. Sci. Ind. Res. 57(1), 41-48, 2022

A Detoxification-Free Process for Enhanced Ethanol Production From Corn Fiber Under Semi-Simultaneous Saccharification and Fermentation

Corn fiber, a by-product from the corn-processing industry, is an attractive feedstock for cellulosic ethanol because of its rich carbohydrate content (mainly residual starch, cellulose, and hemicellulose), abundant reserves, easy collection, and almost no transportation cost. However, the complex structure and components of corn fiber, especially hemicellulose, make it difficult to be effectively hydrolyzed into fermentable sugars through enzymatic hydrolysis. This study developed a simple and easy industrialized process without detoxification treatment for high-yield ethanol produced from corn fiber. Corn fiber was pretreated by dilute acid under the conditions optimized by Box-Behnken design (0.5% H2SO4 at 105°C for 43 min), and 81.8% of total sugars, including glucose, xylose, and arabinose, could be recovered, then the mixture (solid and hydrolysates) was directly used for semi-simultaneous saccharification and fermentation without detoxification, and ethanol yield reached about 81% of the theoretical yield.

Role of nanomaterials in enhanced ethanol production through biological methods – Review on operating factors and machine learning applications

Renewable energy sources based on biomass are identified as sustainable solution to balance the carbon footprint and fuel requirements. The characteristics of bioethanol make it an ideal fuel additive due to its eco-friendliness and calorific value. Fermentation technology is used to convert carbohydrate-rich biomass into biofuel, but technical glitches and high costs have been identified as drawbacks. Nanomaterials have contributed significantly to bioethanol synthesis in terms of enhanced surface activity and selectivity. By using nanoparticles, various steps in the production of bio-alcohol can be made more efficient and cheaper. Based on the extensive review carried out, the best bioethanol yield reported were: dolomite at 121 °C (106%), methyl-functionalized cobalt ferrite– silica at 37 °C (126.9%) and calcium alginate at 37 °C (100%). Magnetic iron oxide covered cellulase yielded 60% in the temperature range of 24–96 °C and Silica-immobilized cellulase yielded 32 g/L at 25–60 °C. Methyl-functionalized cobalt ferrite–silica emerged as an efficient nano-bio catalyst as it gives highest ethanol yield at moderate temperature (37 °C) and pressure (1–2 atm). The mechanism of action of the nanoparticles is discussed in this research and the future directions of research are proposed. Machine learning applications for the prediction of bioethanol yield were discussed in detail.

Protease increases ethanol yield and decreases fermentation time in no-cook process during very-high-gravity ethanol production from rice

No-cook process or Simultaneous Liquefaction, Saccharification, and Fermentation process (SLSF) under very-high-gravity (VHG) condition possesses many advantages for potable ethanol production from rice. The important nutrient that affects the effectiveness of fermentation is nitrogen. Two sources of nitrogen are considered including added urea and indigenous rice protein which can be hydrolysed by an external protease. This study aims to assess the impact of urea and protease on rice conversion, yeast performance including the formation of ethanol and co-products in the SLSF-VHG. The results show that in comparison to the control process (without adding nitrogen), a protease (Fermgen™ 2.5X) supplementation of 600 SAPU/kg rice flour resulted in efficient breakdown of the rice structure along with 2.4% v/v higher ethanol yield and shorter fermentation time of 48 h. Meanwhile, the adding urea at concentration of 16 mM had a slight effect on the structural modification of the rice material without a significant increase (p < 0.05) of final ethanol yield. There was no significant difference (p < 0.05) in ethanol yield between urea and protease addition compared with protease alone. Our results suggested that the addition of protease provided enough nitrogen for yeast by hydrolysing the endogenous rice protein during SLSF-VHG process.

Alkali pretreatment and enzymatic saccharification of blue-green alga Nostochopsis lobatus for bioethanol production

Using various Sodium hydroxide (NaOH) concentrations (0, 1, 2, and 3%), we studied the alkaline pretreatment of microalgal biomass from the blue-green alga Nostochopsis lobatus in this work. In this pretreatment stage, the entrapped polysaccharides found within the microalgae cell walls are broken down to form fermentable subunits. The selected pretreatment procedure (2% NaOH) was then followed by enzymatic saccharification for the generation of bioethanol. This pretreatment step aims to release and break down entrapped polysaccharides in the microalgae cell walls into fermentable subunits. The best result of sugars after enzyme hydrolysis was obtained in total and reducing sugars 210.22 and 98.54 g/L, respectively. In addition, Saccharomyces cerevisiae was used to ferment the hydrolysate; the highest ethanol yield was 14 g/L by 48 hours of fermentation. The alkaline pretreatment method was a promising option for pretreating microalgal biomass for bioethanol production.

Physiological comparisons among Spathaspora passalidarum, Spathaspora arborariae, and Scheffersomyces stipitis reveal the bottlenecks for their use in the production of second-generation ethanol.

The microbial conversion of pentoses to ethanol is one of the major drawbacks that limits the complete use of lignocellulosic sugars. In this study, we compared the yeast species Spathaspora arborariae, Spathaspora passalidarum, and Sheffersomyces stipitis regarding their potential use for xylose fermentation. Herein, we evaluated the effects of xylose concentration, presence of glucose, and temperature on ethanol production. The inhibitory effects of furfural, hydroxymethylfurfural (HMF), acetic acid, and ethanol were also determined. The highest ethanol yield (0.44g/g) and productivity (1.02g/L.h) were obtained using Sp. passalidarum grown in 100g/L xylose at 32°C. The rate of xylose consumption was reduced in the presence of glucose for the species tested. Hydroxymethylfurfural did not inhibit the growth of yeasts, whereas furfural extended their lag phase. Acetic acid inhibited the growth and fermentation of all yeasts. Furthermore, we showed that these xylose-fermenting yeasts do not produce ethanol concentrations greater than 4% (v/v), probably due to the inhibitory effects of ethanol on yeast physiology. Our data confirm that among the studied yeasts, Sp. passalidarum is the most promising for xylose fermentation, and the low tolerance to ethanol is an important aspect to be improved to increase its performance for second-generation (2G) ethanol production. Our molecular data showed that this yeast failed to induce the expression of some classical genes involved in ethanol tolerance. These findings suggest that Sp. passalidarum may have not activated a proper response to the stress, impacting its ability to overcome the negative effects of ethanol on the cells.