Butanol production from sweet sorghum bagasse with high solids content: Part I—comparison of liquid hot water pretreatment with dilute sulfuric acid

In these studies, we pretreated sweet sorghum bagasse (SSB) using liquid hot water (LHW) or dilute H₂SO₄ (2 g L^?1) at 190°C for zero min (as soon as temperature reached 190°C, cooling was started) to reduce generation of sugar degradation fermentation inhibiting products such as furfural and hydroxymethyl furfural (HMF). The solids loading were 250–300 g L^?1. This was followed by enzymatic hydrolysis. After hydrolysis, 89.0 g L^?1 sugars, 7.60 g L^?1 acetic acid, 0.33 g L^?1 furfural, and 0.07 g L^?1 HMF were released. This pretreatment and hydrolysis resulted in the release of 57.9% sugars. This was followed by second hydrolysis of the fibrous biomass which resulted in the release of 43.64 g L^?1 additional sugars, 2.40 g L^?1 acetic acid, zero g L^?1 furfural, and zero g L^?1 HMF. In both the hydrolyzates, 86.3% sugars present in SSB were released. Fermentation of the hydrolyzate I resulted in poor acetone‐butanol‐ethanol (ABE) fermentation. However, fermentation of the hydrolyzate II was successful and produced 13.43 g L^?1 ABE of which butanol was the main product. Use of 2 g L^?1 H₂SO₄ as a pretreatment medium followed by enzymatic hydrolysis resulted in the release of 100.6–93.8% (w/w) sugars from 250 to 300 g L^?1 SSB, respectively. LHW or dilute H₂SO₄ were used to economize production of cellulosic sugars from SSB. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:960–966, 2018     

Enhanced ethanol production by fermentation of rice straw hydrolysate without detoxification using a newly adapted strain of Pichia stipitis

An enhanced inhibitor-tolerant strain of Pichia stipitis was successfully developed through adaptation to acid-treated rice straw hydrolysate. The ethanol production obtained by fermentation of NaOH-neutralized hydrolysate without detoxification using the adapted P. stipitis was comparable to fermentation of overliming-detoxified hydrolysate. The ethanol yield using the adapted P. stipitis with both types of hydrolysate at pH 5.0 achieved 0.45 g_p g_s⁻¹, which is equivalent to 87% of the maximum possible ethanol conversion. Furthermore, the newly adapted P. stipitis demonstrated significantly enhanced tolerance to sulfate and furfural despite the fact that both inhibitors had not been removed from the hydrolysate by NaOH neutralization. Finally, the ethanol conversion could be maintained at 60% and above when the neutralized hydrolysate contained 3.0% sulfate and 1.3 g L⁻¹ furfural.     

Isolation and characterization of Cupriavidus basilensis HMF14 for biological removal of inhibitors from lignocellulosic hydrolysate

The formation of toxic fermentation inhibitors such as furfural and 5-hydroxy-2-methylfurfural (HMF) during acid (pre-)treatment of lignocellulose, calls for the efficient removal of these compounds. Lignocellulosic hydrolysates can be efficiently detoxified biologically with microorganisms that specifically metabolize the fermentation inhibitors while preserving the sugars for subsequent use by the fermentation host. The bacterium Cupriavidus basilensis HMF14 was isolated from enrichment cultures with HMF as the sole carbon source and was found to metabolize many of the toxic constituents of lignocellulosic hydrolysate including furfural, HMF, acetate, formate and a host of aromatic compounds. Remarkably, this microorganism does not grow on the most abundant sugars in lignocellulosic hydrolysates: glucose, xylose and arabinose. In addition, C. basilensis HMF14 can produce polyhydroxyalkanoates. Cultivation of C. basilensis HMF14 on wheat straw hydrolysate resulted in the complete removal of furfural, HMF, acetate and formate, leaving the sugar fraction intact. This unique substrate profile makes C. basilensis HMF14 extremely well suited for biological removal of inhibitors from lignocellulosic hydrolysates prior to their use as fermentation feedstock.     

Effect of inhibitors formed during wheat straw pretreatment on ethanol fermentation by Pichia stipitis

The inhibitory effect of the main inhibitors (acetic acid, furfural and 5-hydroxymethylfurfural) formed during steam explosion of wheat straw was studied through ethanol fermentations of model substrates and hydrolysates from wheat straw by Pichia stipitis. Experimental results showed that an increase in acetic acid concentration led to a reduction in ethanol productivity and complete inhibition was observed at 3.5 g/L. Furfural produced a delay on sugar consumption rates with increasing concentration and HMF did not exert a significant effect. Fermentations of the whole slurry from steam exploded wheat straw were completely inhibited by a synergistic effect due to the presence of 1.5 g/L acetic acid, 0.15 g/L furfural and 0.05 g/L HMF together with solid fraction. When using only the solid fraction from steam explosion, hydrolysates presented 0.5 g/L of acetic acid, whose fermentations have submitted promising results, providing an ethanol yield of 0.45 g ethanol/g sugars and the final ethanol concentration reached was 12.2 g/L (10.9 g ethanol/100 g DM).     

NADH- vs NADPH-coupled reduction of 5-hydroxymethyl furfural (HMF) and its implications on product distribution in Saccharomyces cerevisiae

Saccharomyces cerevisiae alcohol dehydrogenases responsible for NADH-, and NADPH-specific reduction of the furaldehydes 5-hydroxymethyl-furfural (HMF) and furfural have previously been identified. In the present study, strains overexpressing the corresponding genes (mut-ADH1 and ADH6), together with a control strain, were compared in defined medium for anaerobic fermentation of glucose in the presence and absence of HMF. All strains showed a similar fermentation pattern in the absence of HMF. In the presence of HMF, the strain overexpressing ADH6 showed the highest HMF reduction rate and the highest specific ethanol productivity, followed by the strain overexpressing mut-ADH1. This correlated with in vitro HMF reduction capacity observed in the ADH6 overexpressing strain. Acetate and glycerol yields per biomass increased considerably in the ADH6 strain. In the other two strains, only the overall acetate yield per biomass was affected. When compared in batch fermentation of spruce hydrolysate, strains overexpressing ADH6 and mut-ADH1 had five times higher HMF uptake rate than the control strain and improved specific ethanol productivity. Overall, our results demonstrate that (1) the cofactor usage in the HMF reduction affects the product distribution, and (2) increased HMF reduction activity results in increased specific ethanol productivity in defined mineral medium and in spruce hydrolysate.     

Carbon fluxes of xylose-consuming <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> strains are affected differently by NADH and NADPH usage in HMF reduction

Industrial Saccharomyces cerevisiae strains able to utilize xylose have been constructed by overexpression of XYL1 and XYL2 genes encoding the NADPH-preferring xylose reductase (XR) and the NAD⁺-dependent xylitol dehydrogenase (XDH), respectively, from Pichia stipitis. However, the use of different co-factors by XR and XDH leads to NAD⁺ deficiency followed by xylitol excretion and reduced product yield. The furaldehydes 5-hydroxymethyl-furfural (HMF) and furfural inhibit yeast metabolism, prolong the lag phase, and reduce the ethanol productivity. Recently, genes encoding furaldehyde reductases were identified and their overexpression was shown to improve S. cerevisiae growth and fermentation rate in HMF containing media and in lignocellulosic hydrolysate. In the current study, we constructed a xylose-consuming S. cerevisiae strain using the XR/XDH pathway from P. stipitis. Then, the genes encoding the NADH- and the NADPH-dependent HMF reductases, ADH1-S110P-Y295C and ADH6, respectively, were individually overexpressed in this background. The performance of these strains, which differed in their co-factor usage for HMF reduction, was evaluated under anaerobic conditions in batch fermentation in absence or in presence of HMF. In anaerobic continuous culture, carbon fluxes were obtained for simultaneous xylose consumption and HMF reduction. Our results show that the co-factor used for HMF reduction primarily influenced formation of products other than ethanol, and that NADH-dependent HMF reduction influenced product formation more than NADPH-dependent HMF reduction. In particular, NADH-dependent HMF reduction contributed to carbon conservation so that biomass was produced at the expense of xylitol and glycerol formation.     

Effect of surfactants on separate hydrolysis fermentation and simultaneous saccharification fermentation of pretreated lodgepole pine

The effects of surfactants addition on enzymatic hydrolysis and subsequent fermentation of steam exploded lodgepole pine (SELP) and ethanol pretreated lodgepole pine (EPLP) were investigated in this study. Supplementing Tween 80 during cellulase hydrolysis of SELP resulted in a 32% increase in the cellulose‐to‐glucose yield. However, little improvement was obtained from hydrolyzing EPLP in the presence of the same amount of surfactant. The positive effect of surfactants on SELP hydrolysis led to an increase in final ethanol yield after the fermentation. It was found that the addition of surfactant led to a substantial increase in the amount of free enzymes in the 48 h hydrolysates derived from both substrates. The effect of surfactant addition on final ethanol yield of simultaneous saccharification and fermentation (SSF) was also investigated by using SELP in the presence of additional furfural and hydroxymethylfurfural (HMF). The results showed that the surfactants slightly increased the conversion rates of furfural and HMF during SSF process by Saccharomyces cerevisiae. The presence of furfural and HMF at the experimental concentrations did not affect the final ethanol concentration either. The strategy of applying surfactants in cellulase recycling to reduce enzyme cost is presented. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Biohydrogen production from wheat straw hydrolysate by dark fermentation using extreme thermophilic mixed culture

Hydrolysate was tested as substrate for hydrogen production by extreme thermophilic mixed culture (70°C) in both batch and continuously fed reactors. Hydrogen was produced at hydrolysate concentrations up to 25% (v/v), while no hydrogen was produced at hydrolysate concentration of 30% (v/v), indicating that hydrolysate at high concentrations was inhibiting the hydrogen fermentation process. In addition, the lag phase for hydrogen production was strongly influenced by the hydrolysate concentration, and was prolonged from approximately 11 h at the hydrolysate concentrations below 20% (v/v) to 38 h at the hydrolysate concentration of 25% (v/v). The maximum hydrogen yield as determined in batch assays was 318.4 ± 5.2 mL‐H₂/g‐sugars (14.2 ± 0.2 mmol‐H₂/g‐sugars) at the hydrolysate concentration of 5% (v/v). Continuously fed, and the continuously stirred tank reactor (CSTR), operating at 3 day hydraulic retention time (HRT) and fed with 20% (v/v) hydrolysate could successfully produce hydrogen. The hydrogen yield and production rate were 178.0 ± 10.1 mL‐H₂/g‐sugars (7.9 ± 0.4 mmol H₂/g‐sugars) and 184.0 ± 10.7 mL‐H₂/day L_reactor (8.2 ± 0.5 mmol‐H₂/day L_reactor), respectively, corresponding to 12% of the chemical oxygen demand (COD) from sugars. Additionally, it was found that toxic compounds, furfural and hydroxymethylfurfural (HMF), contained in the hydrolysate were effectively degraded in the CSTR, and their concentrations were reduced from 50 and 28 mg/L, respectively, to undetectable concentrations in the effluent. Phylogenetic analysis of the mixed culture revealed that members involved hydrogen producers in both batch and CSTR reactors were phylogenetically related to the Caldanaerobacter subteraneus, Thermoanaerobacter subteraneus, and Thermoanaerobacterium thermosaccharolyticum. Biotechnol. Bioeng. 2010;105: 899–908. © 2009 Wiley Periodicals, Inc.     

Fermentation of lignocellulosic hydrolysate by the alternative industrial ethanol yeast Dekkera bruxellensis

Aim: Testing the ability of the alternative ethanol production yeast Dekkera bruxellensis to produce ethanol from lignocellulose hydrolysate and comparing it to Saccharomyces cerevisiae. Methods and Results: Industrial isolates of D. bruxellensis and S. cerevisiae were cultivated in small‐scale batch fermentations of enzymatically hydrolysed steam exploded aspen sawdust. Different dilutions of hydrolysate were tested. None of the yeasts grew in undiluted or 1 : 2 diluted hydrolysate [final glucose concentration always adjusted to 40 g l^?1 (0·22 mol l^?1)]. This was most likely due to the presence of inhibitors such as acetate or furfural. In 1 : 5 hydrolysate, S. cerevisiae grew, but not D. bruxellensis, and in 1 : 10 hydrolysate, both yeasts grew. An external vitamin source (e.g. yeast extract) was essential for growth of D. bruxellensis in this lignocellulosic hydrolysate and strongly stimulated S. cerevisiae growth and ethanol production. Ethanol yields of 0·42 ± 0·01 g ethanol (g glucose)^?1 were observed for both yeasts in 1 : 10 hydrolysate. In small‐scale continuous cultures with cell recirculation, with a gradual increase in the hydrolysate concentration, D. bruxellensis was able to grow in 1 : 5 hydrolysate. In bioreactor experiments with cell recirculation, hydrolysate contents were increased up to 1 : 2 hydrolysate, without significant losses in ethanol yields for both yeasts and only slight differences in viable cell counts, indicating an ability of both yeasts to adapt to toxic compounds in the hydrolysate. Conclusions: Dekkera bruxellensis and S. cerevisiae have a similar potential to ferment lignocellulose hydrolysate to ethanol and to adapt to fermentation inhibitors in the hydrolysate. Significance and Impact of the study: This is the first study investigating the potential of D. bruxellensis to ferment lignocellulosic hydrolysate. Its high competitiveness in industrial fermentations makes D. bruxellensis an interesting alternative for ethanol production from those substrates.     

Enzymatic saccharification of cornstalk by onsite cellulases produced by Trichoderma viride for enhanced biohydrogen production

Lignocellulosic biomass, if properly saccharified, could be an ideal feedstock for biohydrogen production. However, the high cellulases cost is the key obstacle to its development. In this work, cost‐effective enzyme produced by Trichoderma viride was used to saccharify cornstalk. To obtain high sugar yield, a central composite design of response surface method was used to optimize enzymatic saccharification process. Experimental results showed that the enzymatic saccharification rate reached the highest of 81.2% when pH, temperature, cellulases and substrate concentration were 5, 49.7 °C, 35.7 IU g^?1, and 38.5 g L^?1, respectively. The cornstalk hydrolysate was subsequently introduced to fermentation by Thermoanaerobacterium thermosaccharolyticum W16, the yield of hydrogen reached the highest level of 90.6 ml H₂ g^?1 pretreated cornstalk. The present results indicate the potential of using T. thermosaccharolyticum W16 for high yield conversion of cornstalk hydrolysate, which was saccharified by onsite enzyme produced by T. viride.     

Inhibition analysis of inhibitors derived from lignocellulose pretreatment on the metabolic activity of Zymomonas mobilis biofilm and planktonic cells and the proteomic responses

Lignocellulose pretreatment produces various toxic inhibitors that affect microbial growth, metabolism, and fermentation. Zymomonas mobilis is an ethanologenic microbe that has been demonstrated to have potential to be used in lignocellulose biorefineries for bioethanol production. Z. mobilis biofilm has previously exhibited high potential to enhance ethanol production by presenting a higher viable cell number and higher metabolic activity than planktonic cells or free cells when exposed to lignocellulosic hydrolysate containing toxic inhibitors. However, there has not yet been a systematic study on the tolerance level of Z. mobilis biofilm compared to planktonic cells against model toxic inhibitors derived from lignocellulosic material. We took the first insight into the concentration of toxic compound (formic acid, acetic acid, furfural, and 5‐HMF) required to reduce the metabolic activity of Z. mobilis biofilm and planktonic cells by 25% (IC₂₅), 50% (IC₅₀), 75% (IC₇₅), and 100% (IC₁₀₀). Z. mobilis strains ZM4 and TISTR 551 biofilm were two‐ to three fold more resistant to model toxic inhibitors than planktonic cells. Synergetic effects were found in the presence of formic acid, acetic acid, furfural, and 5‐HMF. The IC₂₅ of Z. mobilis ZM4 biofilm and TISTR 551 biofilm were 57 mm formic acid, 155 mm acetic acid, 37.5 mm furfural and 6.4 mm 5‐HMF, and 225 mm formic acid, 291 mm acetic acid, 51 mm furfural and 41 mm 5‐HMF, respectively. There was no significant difference found between proteomic analysis of the stress response to toxic inhibitors of Z. mobilis biofilm and planktonic cells on ZM4. However, TISTR 551 biofilms exhibited two proteins (molecular chaperone DnaK and 50S ribosomal protein L2) that were up‐regulated in the presence of toxic inhibitors. TISTR 551 planktonic cells possessed two types of protein in the group of 30S ribosomal proteins and motility proteins that were up‐regulated.     

Furfural, 5-hydroxymethyl furfural, and acetoin act as external electron acceptors during anaerobic fermentation of xylose in recombinant Saccharomyces cerevisiae

The electron acceptors acetoin, acetaldehyde, furfural, and 5-hydroxymethylfurfural (HMF) were added to anaerobic batch fermentation of xylose by recombinant, xylose utilising Saccharomyces cerevisiae TMB 3001. The intracellular fluxes during xylose fermentation before and after acetoin addition were calculated with metabolic flux analysis. Acetoin halted xylitol excretion and decreased the flux through the oxidative pentose phosphate pathway. The yield of ethanol increased from 0.62 mol ethanol/mol xylose to 1.35 mol ethanol/mol xylose, and the cell more than doubled its specific ATP production after acetoin addition compared to fermentation of xylose only. This did, however, not result in biomass growth. The xylitol excretion was also decreased by furfural and acetaldehyde but was unchanged by HMF. Thus, furfural present in lignocellulosic hydrolysate can be beneficial for ethanolic fermentation of xylose. Enzymatic analyses showed that the reduction of acetoin and furfural required NADH, whereas the reduction of HMF required NADPH. The enzymatic activity responsible for furfural reduction was considerably higher than for HMF reduction and also in situ furfural conversion was higher than HMF conversion.     

Mild alkaline pretreatment can achieve high hydrolytic and fermentation efficiencies for rice straw conversion to bioethanol

Abstract

Mild alkaline pretreatment was evaluated as a strategy for effective lignin removal and hydrolysis of rice straw. The pretreatment efficiency of different NaOH concentrations (0.5, 1.0, 1.5 or 2.0% w/w) was assessed. Rice straw (RS) pretreated with 1.5% NaOH achieved better sugar yield compared to other concentrations used. A cellulose conversion efficiency of 91% (45.84?mg/ml glucose release) was attained from 1.5% NaOH pretreated rice straw (PRS), whereas 1% NaOH pretreated rice straw yielded 35.10?mg/ml of glucose corresponding to a cellulose conversion efficiency of 73.81%. The ethanol production from 1% and 1.5% NaOH pretreated RS hydrolysates was similar at ～3.3% (w/v), corresponding to a fermentation efficiency of 86%. The non-detoxified hydrolysate was fermented using the novel yeast strain Saccharomyces cerevisiae RPP-03O without any additional supplementation of nutrients.     

Detoxification of a lignocellulosic biomass slurry by soluble polyelectrolyte adsorption for improved fermentation efficiency

This study investigated the detoxification of a dilute acid pretreated Ponderosa pine slurry using the polyelectrolyte polyethyleneimine (PEI). The addition of polyelectrolyte to remove enzymatic and/or fermentation inhibitory compounds, that is, acetic acid, furfural, and 5-hydroxymethylfurfural (HMF), was performed either before or after enzymatic hydrolysis to determine the optimal process sequence. Negligible acetic acid, glucose, and xylose were removed regardless of where in the process the polymer addition was made. Maximum furfural and HMF separation was achieved with the addition of PEI to a clarified pre-enzymatic hydrolysis liquor, which showed that 88.3% of furfural and 66.4% of HMF could be removed. On the other hand, only 23.1% and 13.4% of furfural and HMF, respectively, were removed from a post-enzymatic hydrolysis sample; thus, the effects of enzymes, glucose, and wood solids on inhibitor removal were also investigated. The presence of solid particles >0.2 μm and unknown soluble components <10 kDa reduced inhibitory compound removal, but the presence of elevated glucose levels and enzymes (cellulases) did not affect the separation. The fermentability of detoxified versus undetoxified hydrolysate was also investigated. An ethanol yield of 92.6% of theoretical was achieved with Saccharomyces cerevisiae fermenting the detoxified hydrolyzate, while no significant ethanol was produced in the undetoxified hydrolyzate. These results indicate that PEI may provide a practical alternative for furan removal and detoxification of lignocellolosic hydrolysates, and that application before enzymatic hydrolysis minimizes separation interferences.     

Effect of inoculum level on xylitol production from rice straw hemicellulose hydrolysate byCandida guilliermondii

The effect of inoculum level on xylitol production byCandida guilliermondii was evaluated in a rice straw hemicellulose hydrolysate. High initial cell density did not show a positive effect in this bioconversion since increasing the initial cell density from 0.67 g L^–1 to 2.41 g L^–1 decreased both the rate of xylose utilization and xylitol accumulation. The maximum xylitol yield (0.71 g g^–1) and volumetric productivity (0.56 g L^–1 h^–1) were reached with an inoculum level of 0.9 g L^–1. These results show that under appropriate inoculum conditions rice straw hemicellulose hydrolysate can be converted into xylitol by the yeastC. guilliermondii with efficiency values as high as 77% of the theoretical maximum.     

Continuous multistep versus fed‐batch production of ethanol and xylitol in a simulated medium of sugarcane bagasse hydrolyzates

Co‐cultures for simultaneous production of ethanol and xylitol were studied under different operation bioreactor modes using Candida tropicalis IEC5‐ITV and Saccharomyces cerevisiae ITV01‐RD in a simulated medium of sugarcane bagasse hydrolyzates. Xylitol and ethanol tolerance by S. cerevisiae and C. tropicalis, respectively, was evaluated. The results showed that C. tropicalis was sensitive to ethanol concentrations up to 30 g/L, while xylitol had no effect on S. cerevisiae viability and metabolism. The best condition found for simultaneous culture was S. cerevisiae co‐culture and C. tropicalis sequential cultivation at 24 h. Under these conditions, productivity and yield for ethanol were Q_EtOH = 0.72 g L^?1 h^?1 and Y_EtOH/s = 0.37 g/g, and for xylitol, Q_XylOH = 0.10 g L^?1 h^?1 and Y_XylOH/S = 0.31 g/g, respectively; using fed‐batch culture, the results were Q_EtOH = 0.87 g L^?1 h^?1 and Y_EtOH/s = 0.44 g L^?1 h^?1, and Q_EtOH = 0.27 g L^?1 h^?1 and Y_EtOH/s = 0.57 g/g, respectively. Maximum volumetric productivity in continuous multistep cultures of ethanol and xylitol was at dilution rates of 0.131 and 0.074 h^?1, respectively. Continuous multistep production, Q_EtOH increased up to 50% more than in fed‐batch culture, even though xylitol yield remained unchanged.     

Bioethanol fermentation of concentrated rice straw hydrolysate using co-culture of Saccharomyces cerevisiae and Pichia stipitis

Rice straw is one of the abundant lignocellulosic feed stocks in the world and has been selected for producing ethanol at an economically feasible manner. It contains a mixture of sugars (hexoses and pentoses).Biphasic acid hydrolysis was carried out with sulphuric acid using rice straw. After acid hydrolysis, the sugars, furans and phenolics were estimated. The initial concentration of sugar was found to be 16.8 g L⁻¹. However to increase the ethanol yield, the initial sugar concentration of the hydrolysate was concentrated to 31 g L⁻¹ by vacuum distillation. The concentration of sugars, phenols and furans was checked and later detoxified by over liming to use for ethanol fermentation. Ethanol concentration was found to be 12 g L⁻¹, with a yield, volumetric ethanol productivity and fermentation efficiency of 0.33 g L⁻¹ h⁻¹, 0.4 g g⁻¹ and 95%, respectively by co-culture of OVB 11 (Saccharomyces cerevisiae) and Pichia stipitis NCIM 3498.     

Oil production by oleaginous yeasts using the hydrolysate from pretreatment of wheat straw with dilute sulfuric acid

This paper explores the use of the hydrolysate from the dilute sulfuric acid pretreatment of wheat straw for microbial oil production. The resulting hydrolysate was composed of pentoses (24.3 g/L) and hexoses (4.9 g/L), along with some other degradation products, such as acetic acid, furfural, and hydroxymethylfurfural (HMF). Five oleaginous yeast strains, Cryptococcus curvatus, Rhodotorula glutinis, Rhodosporidium toruloides, Lipomyces starkeyi, and Yarrowia lipolytica, were evaluated by using this hydrolysate as substrates. The results showed that all of these strains could use the detoxified hydrolysate to produce lipids while except R. toruloides non-detoxified hydrolysate could also be used for the growth of all of the selective yeast strains. C. curvatus showed the highest lipid concentrations in medium on both the detoxified (4.2 g/L) and non-detoxified (5.8 g/L) hydrolysates. And the inhibitory effect studies on C. curvatus indicated HMF had insignificant impacts at a concentration of up to 3 g/L while furfural inhibited cell growth and lipid content by 72.0% and 62.0% at 1 g/L, respectively. Our work demonstrates that lipid production is a promising alternative to utilize hemicellulosic sugars obtained during pretreatment of lignocellulosic materials.     

Evaluation of fermentative potential of <Emphasis Type="Italic">Kluyveromyces marxianus</Emphasis> ATCC 36907 in cellulosic and hemicellulosic sugarcane bagasse hydrolysates on xylitol and ethanol production

This paper evaluates the fermentative potential of Kluyveromyces marxianus grown in sugarcane bagasse cellulosic and hemicellulosic hydrolysates obtained by acid hydrolysis. Ethanol was obtained from a single glucose fermentation product, whereas xylose assimilation resulted in xylitol as the main product and ethanol as a by-product derived from the metabolism of this pentose. Fermentation performed in a simulated hydrolysate medium with a glucose concentration similar to that of the hydrolysate resulted in ethanol productivity (Qp?=?0.86 g L^?1 h^?1) that was tenfold higher than the one observed in the cellulosic hydrolysate. However, the use of hemicellulosic hydrolysate favored xylose assimilation in comparison with simulated medium with xylose and glucose concentrations similar to those found in this hydrolysate, without toxic compounds such as acetic acid and phenols. Under this condition, xylitol yield was 53.8 % higher in relation to simulated medium. Thus, the total removal of toxic compounds from the hydrolysate is not necessary to obtain bioproducts from lignocellulosic hydrolysates.