Simultaneous Saccharification Research Articles

Biochemical and Biorefinery Platform for Second-Generation Bioethanol: Fermentative Strategies and Microorganisms

Bioethanol is the most commonly used biofuel. It is an alternative to replace fossil fuels in renewable energy; it can be produced from lignocellulosic feedstock using a biotechnological process. Their participation of microorganisms is crucial in the bioconversion process of fermentation for ethanol production and can involve bacteria, fungi, and yeasts. However, when working within bioethanol processes from lignocellulose feedstock, microorganisms face some challenges, such as high temperature, high solids content, and the ability to ferment sugars for high ethanol concentration. Such challenges will depend on operative strategies, such as simultaneous saccharification and fermentation, separate hydrolysis and fermentation, semi-simultaneous saccharification and fermentation, and consolidated bioprocessing; these are the most common configurations. This review presents different trends of the microbial role, biochemical application, and fermentation operative strategies for bioethanol production of the second generation.

The enhancement of ethanol production from NaOH-catalyzed organosolv pretreated poplar with compound additives

In this study, different additives (such as Bovine serum albumin (BSA), PEG 8000, calcium lignosulfonate, tea saponin, and Tween 80) were introduced to enhance the efficiency of simultaneous saccharification and fermentation (SSF) of NaOH-catalyzed organosolv pretreated poplar. Then the influence of two-factor additive compound on SSF was determined, only 75 mg/g BSA had a positive interaction with 150 mg/g tea saponin, which generated the maximal ethanol yield of 92.83 % with ethanol concentration of 18.82 g/L after 24 h, ascribing to the higher relative enzyme activity, free enzyme, and Zeta potential. Furthermore, with the addition of combined additives at an enzyme dosage of 8 FPU/g substrate, the NaOH-catalyzed organosolv pretreated poplar liberated higher ethanol than that without additive at an enzyme dosage of 15 FPU/g substrate. This phenomenon indicated that the use of combined additive can improve fermentation efficiency, while reducing almost 1/2 enzyme dosage. In general, this study provided a facile and efficient method for ethanol production with compound additives.

A Short Review of Second-Generation Isobutanol Production by SHF and SSF

As isobutanol exhibits higher energy density and lower hygroscopicity than ethanol, it is considered a better candidate biofuel. The sustainable supply of inedible biomass and lack of competition with the food supply have stimulated significant worldwide interest in the production of isobutanol from this resource. Both separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) have been applied to isobutanol production to effectively utilize inedible biomass as a feedstock. However, both processes have various challenges, including low isobutanol yield and high production costs. This review summarizes the potential of isobutanol as a biofuel, methods for conferring isobutanol productivity, recent experimental studies, and developments in both SHF and SSF with the isobutanol-producing strains. Challenges to increasing the isobutanol yield and various suggestions for improvements to enable commercial production are also discussed.

Daqu regulates the balance of saccharification and alcoholic fermentation to promote Chinese baijiu fermentation

Saccharifying activity of starter culture plays a key role on the simultaneous saccharification and fermentation of Chinese baijiu fermentation. However, the regulation of alcoholic fermentation by Daqu starter or saccharifying enzymes still remains unclear in the baijiu fermentation. In this study, we identified 13 proteins, affiliated to 4 saccharifying enzymes (including alpha-amylase, beta-amylase, glucoamylase and beta-glucosidase) as the key saccharifying enzymes in Daqu by metaproteomic and culture-dependent analysis. These enzymes were metabolized from plant substrate (13.4%) and microbial metabolism (86.6%), and especially alpha-amylase and glucoamylase from Aspergillus and Rhizopus were dominant in Daqu bio-system. Furthermore, we observed the dynamic of saccharifying activity of Daqu (from 241 to 395 U) was driven by the combinations of isolated saccharifying microbes responsible for key enzymes releasing, indicating AR7 group (with a ration of Rhizopus oryzae: Aspergillus oryzae in 10:1) presented the highest saccharifying activity (395 U) in a simulative Daqu production. However, the highest ethanol production (80.5 mg/g) was obtained from the fermentation driven by AR8 group (with a ration of Rhizopus oryzae: Aspergillus oryzae in 50:1) with the saccharifying activity of 389 U. These results indicated that a proper combination of saccharifying microbes could enhance the saccharifying activity of Daqu and then promote ethanol production in baijiu fermentation, as it did not always exhibit a positive correlativity between saccharifying activity and alcoholic fermentation. Our findings should provide a potential approach to regulate the alcoholic fermentation by optimizing the saccharifying microbes or enzymes of starter cultures for baijiu and other fermented food.

Production of ethanol from oil palm trunk by simultaneous saccharification and fermentation process at bench scale

Abstract A largenumber of oil palm trees are replanted every year. Considering the extent of replanting and OPT’s high starch and sugar content, it was determined to be a potential raw material for bioethanol production. This study conducted ethanol production by simultaneous saccharification and fermentation of starch-rich powder extracted from oil palm trunks. Fermentation was conducted on a 100 L bench scale to evaluate the feasibility and further development of the process before the process is implemented at a larger scale. The preparation of the starch-rich flour involves shredding, drying, and screening of the trunks until the starch-rich powder passes through an 80-mesh sieve. Furthermore, starch was liquefied and partially saccharified. Subsequent saccharification was performed simultaneously with fermentation. The initial total sugar content was adjusted to 15 % w/v and starch was enzymatically hydrolyzed using commercial α-amylase (Liquozyme) and glucoamylase (Novozyme) produced by NOVO. Fermentation was performed using Saccharomyces cerevisiae Hakken No. 1. Since the starch-rich flour contains useful nutrients and growth factors for microbes, the fermentation medium only required the addition of a nitrogen source (urea 1 g/L). The ethanol content after fermentation was approximately 8.7 % v/v with a fermentation ratio of 88.8 %. These results were obtained at a fermentation time of 60 h. One OPT yields 80 kg of starch-rich powder, equivalent to 33 liters of bioethanol.

Techno-economical valorization of sugarcane bagasse for efficiently producing optically pure D-(−)-lactate approaching the theoretical maximum yield in low-cost salt medium by metabolically engineered Klebsiella oxytoca

Sugarcane bagasse (SCB) was utilized for efficiently producing optically pure D-(−)-lactate by Klebsiella oxytoca KIS004-91T strain. Cellulase (15 U/g NaOH-treated SCB) sufficiently liberated high sugars with saccharifications of 79.8 % cellulose and 52.5 % hemicellulose. For separated hydrolysis and fermentation, D-(−)-lactate was produced at 53.5 ± 2.1 g/L (0.98 ± 0.01 g/g sugar utilized or 0.71 ± 0.01 g/g total sugars) while D-(−)-lactate at 47.2 ± 1.8 g/L (0.78 ± 0.03 g/g sugar used or 0.69 ± 0.01 g/g total sugars) was obtained under simultaneous saccharification and fermentation (SSF). D-(−)-lactate at 99.9 ± 0.9 g/L (0.97 ± 0.01 g/g sugar utilized or 0.78 ± 0.01 g/g total sugars) was improved via fed-batch SSF. Based on mass balance, raw SCB of 7 kg is required to produce 1 kg D-(−)-lactate. Unlike others, D-(−)-lactate production was performed in low-cost salt medium without requirements of rich nutrients. Costs regarding medium, purification, and waste disposal may be reduced. This unlocks economic capability of SCB bioconversion or agricultural and agro-industrial wastes into high valuable D-(−)-lactate.

Enhancing efficiency in ethanol production from high solid corn stover: Insights into enzymatic hydrolysis parameters and cellulase recovery

BackgroundThe simultaneous saccharification and co-fermentation (SSCF) at high solid loading is an effective approach to improve the economic feasibility of bioethanol. MethodsIn this study, the high-solid SSCF of superfine grinding corn stover was treated with cheap and readily available deionized water (DW) instead of sodium citrate buffer solution (SCBS). Additionally, the evaluation of temperature, enzyme loading, solid loading, and cellulose recovery were carried out to determine their impact on ethanol production. Significant FindingsThe results of the analysis indicated that replacing SCBS with DW had negligible effects on the SSCF of ethanol and byproducts (acetic acid and glycerol). The ethanol yield increased by 18 % at 35 °C compared to the yield at 30 °C. As enzyme loading increased, more cellulose active sites in corn stover were bound by cellulase, which increased the ethanol yield by improving the efficiency of enzymatic hydrolysis. The SSCF process didn't incorporate any buffer, resulting in an even higher ethanol titer (55.42 g/L). Furthermore, the cellulase productivity increased by 71 % after recovery, compared to the non-recovery. The results indicated that the optimized SSCF process is a potential technique for producing bioethanol on a commercial level because it improves the production efficiency while keeping costs low.

Efficient Biovalorization of Oil Palm Trunk Waste as a Low-Cost Nutrient Source for Bioethanol Production

This study aimed to efficiently utilize felled oil palm trunk (OPT) for bioethanol and lactic acid production. OPT was separated into two fractions: oil palm sap (OPS) and OPT fiber. OPS contained substantial amounts of sugars (38–40 g/L) and nitrogen (0.60–0.70 g/L), which can serve as a base medium for bioethanol production. As bioethanol production requires high sugar concentrations, OPS was concentrated, supplemented with OPT fiber, and used for bioethanol production through simultaneous saccharification and fermentation (SSF) by Saccharomyces cerevisiae. Repeated-batch SSF for five cycles efficiently utilized OPT fiber and achieved an average ethanol production of 35–42 g/L in each cycle. To increase the accessibility of the enzyme, OPT fiber was acid-pretreated prior to the SSF process. The combined use of acid-pretreated OPT slurry and concentrated OPS provided the maximum ethanol production of 49.63 ± 1.05 g/L. The fermented broth after ethanol recovery, containing mainly xylose, was used to produce lactic acid at a concentration of 18.85 ± 0.55 g/L. These strategies can greatly contribute to the zero-waste biorefinery of OPT and may also be applicable for the efficient biovalorization of other similar agricultural wastes.

Inhibitor Tolerance Capacity of Pichia kudriavzevii NBRC1279 and NBRC1664

The thermotolerant yeast Pichia kudriavzevii (previously known as Issatchenkia orientalis), can produce ethanol from a variety of carbon sources and grows at around 45 °C. Thus, this yeast is considered a useful biocatalyst for producing ethanol from lignocellulose through simultaneous saccharification and fermentation (SSF). SSF has several advantages, such as a simplified manufacturing process, ease of operation and reduced energy input. Using P. kudriavzevii NBRC1279 and NBRC1664, we previously succeeded in producing ethanol through SSF; however, the extent to which inhibitors by-produced from lignocellulose hydrolysis affect the growth and ethanol productivity of the two strains remains to be investigated. In this study, to better understand the inhibitor tolerance capacity of the two strains, spot assay, growth experiment, real-time quantitative PCR (RT-qPCR) analysis and multiple sequence alignment analysis were carried out. When P. kudriavzevii NBRC1279 and NBRC1664, as well as Saccharomyces cerevisiae BY4742 as a control, were cultured on SCD plates containing 17% ethanol, 42 mM furfural, 56 mM 5-hydroxymethylfurfural (HMF) or 10 mM vanillin, only P. kudriavzevii NBRC1664 was able to grow under all conditions. Moreover, the inhibitor tolerance capacity of P. kudriavzevii NBRC1664 was greater than those of other strains using SCD medium containing the same concentrations of various inhibitors. When an RT-qPCR analysis of seven gene sequences from aldehyde dehydrogenase and the aldehyde dehydrogenase family protein (ADHF) was performed using P. kudriavzevii NBRC1664 cultivated in the presence of 56 mM HMF, ADHF1 and ADHF2 were up-regulated in the early logarithmic growth phase. Moreover, a multiple sequence alignment of the amino acid sequences of ADHF1, ADHF2 and the known ADH suggested that ADHF1 and ADHF2 may catalyze the reversible NAD+-dependent oxidation of HMF. Our data may be useful for future studies on the metabolic engineering of more useful strains for ethanol production from lignocellulose.

Production of Ethanol from Green Coconut Fiber by Integrating Cloud Point Extraction and Simultaneous Saccharification and Fermentation

Production of Ethanol from Green Coconut Fiber by Integrating Cloud Point Extraction and Simultaneous Saccharification and Fermentation

Ethanol production from the wood and fruit juice of paper mulberry via simultaneous saccharification and juice co-fermentation under normal and very high gravity conditions

A novel batch simultaneous saccharification and juice co-fermentation (SSJcF) process was investigated using mixtures of PHP (phosphoric acid plus hydrogen peroxide) pretreated wood and fruit juice of paper mulberry tree. All the different substrate mixture configurations evaluated under normal gravity SSJcF (total sugar titer of 180 g/L) significantly improved both ethanol concentration and yield compared to sole simultaneous saccharification and fermentation (SSF) of paper mulberry wood. Among the different mixing ratios, the feedstock mixture with equal sugar content from each substrate resulted in maximum ethanol concentration, yield and productivity of 77.1 g/L, 83.9 % and 1.1 g/L/h, respectively. The external additions of mineral nutrients also had no impact on fermentation performance of the mixture. Furthermore, SSJcF was evaluated under different levels of high gravity (HG) and very high gravity (VHG) conditions. The total sugar titer of 350 g/L at equal contributions from each substrate reached very high ethanol concentration of 147.0 g/L, with yield and productivity of 82.3 % and 1.5 g/L/h, respectively. By implication, the PM wood and fruit juice mixture could serve as suitable low-cost and non-food feedstock alternative to the typical use of sugary and/or starchy feedstocks for VHG fermentation.

Comparison of lactic and propionic acid hydrolysis for production of xylo-oligosaccharides and ethanol from polysaccharides in Toona sinensis branch

Xylan-type hemicellulose hydrolysis by an organic acid solution for the production of xylo-oligosaccharides (XOS) is efficient and eco-friendly, but the effects of different organic acids on XOS production from Toona sinensis branch (TB) biomass is limited. In this work, under the conditions of 170 °C for 60 min, 33.1 % and 38.7 % XOS yields were obtained from polysaccharides present in TB by 2 % lactic acid (LA) and 6 % propionic acid (PA), respectively. Then 77 % of the lignin was removed by hydrogen peroxide−acetic acid pretreatment system, and 39.5 % and 44.7 % XOS yield were obtained from polysaccharides in delignification TB by 2 % LA and 6 % PA, respectively. It was found that PA hydrolysis, especially from delignified TB, resulted in higher XOS yield and purity compared to LA hydrolysis. Moreover, the content of byproducts (xylose, hydroxymethyl-furfural and furfural) in PA hydrolysate was lower. Following the hydrolysis process, the simultaneous saccharification and fermentation of the TB solid residue achieved an ethanol yield of 71.5 %. This work proposed an integrated process to preferentially convert the TB hemicellulose into valuable XOS and then convert the cellulose into ethanol. This process had the advantages of eliminating the need for isolation and purification of xylan, and the potential to obtain multiple products from the same raw material.

Co-fermentation exploiting glucose and xylose utilizing thermotolerant S. cerevisiae of highly lignified biomass for biofuel production: Statistical optimization and kinetic models

The present study assesses the potential of co-fermentation for the enhanced production of biofuels from a highly lignified biomass, Viz., Pomegranate Peel (PP) and Mosambi Peel (PP). The simultaneous saccharification and co-fermentation (SScF) on brewer's yeast Saccharomyces cerevisiae and modified strain S. cerevisiae XUSE were used for the ethanol production using RSM. The Box-Behnken design (BBD) model was used to execute 15 runs with independent factors of initial pH (5.5, 6.5, 7.5), yeast concentration (4%, 5% and 6%v/v), and co-culture yeast concentration (4%, 5% and 6%v/v). The highest bioethanol production was achieved by PP (35.460 ± 0.32 g/L) and MP (25.630 ± 0.40 g/L) on optimal variables of pH 6.5, with yeast concentration (5% v/v) and co-culture yeast concentration (5% v/v) for 120 hrs duration. Furthermore, the kinetic of logistic and modified Gompertz model analyzed the lag phase of PP and MP was 7.9 and 7.15 h, for which maximum bioethanol production (EtOH max-Pm) reported for PP (38.62 g/L) and MP (29.21 g/L), respectively. The study infers that SScF has great potential for producing high-titer ethanol commercially and supports waste-to-energy strategies.

Bio-2,3-butanediol production from banana waste: Preliminary techno-economic evaluation of processing strategies

This study evaluates different fermentation strategies to produce 2,3-butanediol (2,3-BD) from banana industry waste, such as whole bananas (fruit + peels) and banana peels, selecting the most favorable from a technical and economic point of view. Both residues have enough free sugars (17.8 %–35.8 %), glucan (11.0 %–14.2 %) and hemicellulose (2.8 %–6.3 %), to be promising substrates for 2,3-BD fermentation. Saccharification was studied by comparing enzymatic hydrolysis, hydrothermal pretreatment, and hydrothermal pretreatment followed by enzymatic hydrolysis. Different fermentation scenarios were also compared regarding the 2,3-BD yield and productivity: Separate Hydrolysis and Fermentation (SHF), Simultaneous Saccharification and Fermentation (SSF), and direct fermentation without prior saccharification using Paenibacillus polymyxa DSM-365 as the fermenting microorganism. The results showed that the pretreatment step was not necessary to improve the release of fermentable sugars. Enzymatic hydrolysis was the most effective alternative for maximizing sugar recovery, reaching sugar concentrations of 18.1 g/L (recovery: 92.5 %) for banana peels and 33.3 g/L (recovery: ∼100 %) for whole bananas. The SSF strategy led to higher 2,3-BD concentrations of 15.0 g/L and 26.6 g/L for banana peels and whole bananas, respectively. The preliminary economic analysis indicated that SSF and direct fermentation could be the more cost-effective process alternatives for banana peels and whole bananas, respectively. Thus, it was demonstrated that banana waste is an interesting resource for the production of 2,3-BD. The bioprocess can be competitive when using a low-cost raw material and reducing the number of process steps compared to traditional technologies.

Assessment of Lignin Residues from Bioethanol Production of Olive Stones as Green Chemical Thickener of Epoxidized Linseed Oil

This work focused on the characterization of lignin residues from bioethanol production of olive stones (OS) and the use of these residues to chemically thicken epoxidized linseed oil (ELO). OS were processed by an acid/steam explosion pretreatment, followed by pre-saccharification, using different enzyme dosages, and simultaneous saccharification and fermentation. The chemical composition of the OS lignin residues was analysed, revealing a high lignin content (66.6–69.5%), and lower quantities of glucan (17.4–19.3%) and xylan (2.8–2.9%). Whereas, the structural properties of OS lignin residues were characterized by Fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), thermogravimetric analysis and size exclusion chromatography (SEC). OS lignin residues displayed the main inter-unit linkages (β–β′ resinol (51.0–59.0%), followed by β-O-4′ alkyl aryl ethers (27.0–35.2%) and β-5′ phenylcoumaran (11.4–13.2%) substructures), high molecular weights (22,000–25900 Da), low S/G ratios (1.2–1.5) and phenolic groups content (48–55 mg GAE/g lignin). Moreover, OS lignin residues were dispersed in ELO to obtain thickened formulations, which were characterized by FTIR and NMR. Oil thickening was achieved by promoting the chemical crosslinking between lignocellulose hydroxyl groups and ELO epoxy groups, enabling the compatibilization of both components. Up to tenfold viscosity increment of the resulting thickened formulations in relation to ELO’s viscosity was observed. Besides, thickened formulations exhibited viscoelastic properties, evincing oil structuration to some extent.Graphical

Olive leaves upgrading applying a novel two-stage organosolv pretreatment: Techno-economic and environmental assessment

This research study evaluates the techno-economic and environmental performance of an olive leaves based biorefinery to produce antioxidants, bioethanol, and organosolv lignin. The biorefinery comprises processes such as organosolv extraction, organosolv pretreatment and simultaneous saccharification and fermentation, which were simulated in Aspen Plus v9.0. Experimental data were used to simulate the process, assuming a linear up-scaling. The techno-economic evaluation was carried out considering financial indicators such as net present value (NPV) and internal rate of return (IRR). The environmental assessment was done applying the life cycle assessment methodology. The results shows that 100 g olive leaves can produce 16.58 g antioxidant extract, 11.12 g organosolv lignin, and 2.85 g bioethanol. The proposed biorefinery was feasible at a processing scale of 30,000 t/y with a NPV of 47.9 million USD and an internal rate of return of 27.8%. The proposed biorefinery can be implemented in Jaén (Andalusia-Spain) based on the high amount of olive leaves produced in this region. Stillages are the most polluting waste stream of the process. The carbon footprint of the biorefinery was 1.13 kgCO2-eq/kg olive leaves. The application of the biorefinery concept revealed that olive leaves could be transformed into value-added products from a techno-economic and environmental perspective.

Simultaneous Saccharification and Fermentation (SSF) of Blended Organic Fertilizer from Yam and Sweet Potato Peels

This study shows the production of organic fertilizer by utilization of yam and sweet potatoes peels through Simultaneous Saccharification and Fermentation (SSF) Method. Samples are categorized into sun-dried, sundried and autoclaved, Heat-dried, heat-dried and autoclaved, the fermentation process is carried out using alpha amylase and saccharomyces cerevisiae. Investigation of mineral elements (N, Cd, P, Zn, Pb, As, K, Hg.), in the eight varieties of Organic Fertilizer produced shows concentration of Cadmium (Cd) ranges from 0.0015 mg/kg to 0.0033 mg/kg), Nitrogen (N) in Percentage ranges from 2.3450% to 3.8550%; Phosphorus (P) ranges from 2.345 mg/kg to 3.607 mg/kg; Zinc (Zn) ranges from 2.215 mg/kg to 6.335 mg/kg. Lead (Pb) ranges from 0.00 mg/kg to 0.0015 mg/kg, potassium (K) ranges from 3.952 mg/kg to 6.213 mg/kg; Mercury and Arsenic nil. The study shows that Sweet Potato Peel (SDSPP) contains high Cadmium and potassium compare to other organic fertilizer produced. Sundried and Autoclaved Yam Peel (SDAYP) contains high percentage of Nitrogen (N), Heat Dried and Autoclaved Sweet Potato Peel (HDASPP) contains low Nitrogen, Sundried and Autoclaved Sweet Potato Peel (SDASPP) contains low phosphorus, Sundried Yam Peel (SDYP), Sundried and Autoclaved Yam Peels (SDAYP), Heat Dried Sweet Potato Peel HDSPP and Heat Dried Sweet Potato Peel (HDSPP) has zero trace of Lead (Pb) making it free of food intoxication from heavy metals, SDYP contains high phosphorus. These indicate that the samples will make quality organic fertilizer because it contains high Nitrogen, Phosphorus and potassium (NPK) which are essential elements required in plant structures.

Third-generation D-lactic acid production using red macroalgae Gelidium amansii by co-fermentation of galactose, glucose and xylose

Macroalgae biomass has been considered as a promising renewable feedstock for lactic acid production owing to its lignin-free, high carbohydrate content and high productivity. Herein, the D-lactic acid production from red macroalgae Gelidium amansii by Pediococcus acidilactici was investigated. The fermentable sugars in G. amansii acid-prehydrolysate were mainly galactose and glucose with a small amounts of xylose. P. acidilactici could simultaneously ferment the mixed sugars of galactose, glucose and xylose into D-lactic acid at high yield (0.90 g/g), without carbon catabolite repression (CCR). The assimilating pathways of these sugars in P. acidilactici were proposed based on the whole genome sequences. Simultaneous saccharification and co-fermentation (SSCF) of the pretreated and biodetoxified G. amansii was also conducted, a record high of D-lactic acid (41.4 g/L) from macroalgae biomass with the yield of 0.34 g/g dry feedstock was achieved. This study provided an important biorefinery strain for D-lactic acid production from macroalgae biomass.

Enhancing simultaneous saccharification and co-fermentation of corncob by Kluyveromyces marxianus through overexpression of putative transcription regulator

Overexpression of a gene with unknown function in Kluyveromyces marxianus markedly improved tolerance to lignocellulosic biomass-derived inhibitors. This overexpression also enhanced tolerance to elevated temperatures, ethanol, and high concentrations of NaCl and glucose. Inhibitor degradation and transcriptome analyses related this K. marxianusMultiple Stress Resistance (KmMSR) gene to the robustness of yeast cells. Nuclear localization and DNA-binding domain analyses indicate that KmMsr is a putative transcriptional regulator. Overexpression of a mutant protein with deletion in the flexible region between amino acids 100 and 150 further enhanced tolerance to multiple inhibitors during fermentation, with ethanol production and productivity increasing by 36.31 % and 80.22 %, respectively. In simultaneous saccharification co-fermentation of corncob without detoxification, expression of KmMSR with the deleted flexible region improved ethanol production by 5-fold at 42 °C and 2-fold at 37 °C. Overexpression of the KmMSR mutant provides a strategy for constructing robust lignocellulosic biomass using strains.

Simultaneous Saccharification and Fermentation for Isobutanol Production from Banana Peel

Each year, near 40 million tons of banana peels are discarded around the world. This plant biomass could potentially be utilized for energy production. Simultaneous saccharification and fermentation (SSF) is an effective method for producing biofuels from plant biomasses. Since SSF with enzymatic hydrolysis and fermentation are performed simultaneously in the same reactor, the production process is simpler than most existing methods. Here, we describe isobutanol production using SSF with hydrothermally treated banana peel samples and an Escherichia coli strain able to utilize glucose and xylose to produce isobutanol. To enhance the glucose and xylose concentrations, the reaction conditions for the enzymatic hydrolysis of plant biomass using two kinds of saccharification enzymes were optimized, including the enzyme unit ratio, reaction temperature and sample gram. When the optimized conditions for enzymatic hydrolysis were applied to SSF, the glucose and xylose produced from the hydrothermally treated samples were consumed, producing isobutanol. Moreover, the isobutanol concentration increased with an increasing initial culture pH, reaching 1.27 g/L at pH 6.5, which was consistent with the optimal initial culture pH for isobutanol production by this E. coli strain. Taken together, these results indicate that the established method is potentially useful for industrial isobutanol production.